I think I might need a new car battery charger. However I'm failing to find
anything suitable and wonder if the team can recommend any models.

Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery. My
current 1980s dumb-charger can't handle delivering current into a low
voltage battery for more than a few seconds before the thermal trip goes[1].
I've seen smart chargers say 'we handle flat batteries 7.5V' which is no
use when the voltage drops below that.[2]

I would expect that mode to be a constant current mode, although they could
pulse or do other fancy things. But it should be able to deliver it
continuously without tripping out.

Requirement #2 is a display of voltage and current so I can see what's going
on. Little LEDs saying 'half' or 'full' do not cut it.

Nice-to-have #3 is a means of terminating charge when it's full, but I could
live without that.


Are there any 'smart' chargers that aren't also 'too clever for their own
good' chargers?

Thanks
Theo


[1] Instead I've been using a old 32V 2A bench PSU in constant current mode,
but 2A isn't very much and the case gets very hot (suspect a linear PSU).
It also isn't great to leave in the engine bay as it isn't weatherproofed in
any way.

[2] You might say the battery has had it by this point, but it's an AGM
battery in a hybrid so it lives an easy life. It only needs to provide 20A
for a few seconds to open contactors, it isn't used to start the car. I
might look at a LiFePO4 SLA-replacement next time.

On Tue, 21 Jul 2020 22:26:18 +0100 (GMT+01:00), Jimk
wrote:

Theo Wrote in message:
I think I might need a new car battery charger. However I'm failing to find
anything suitable and wonder if the team can recommend any models.

Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery. My
current 1980s dumb-charger can't handle delivering current into a low
voltage battery for more than a few seconds before the thermal trip goes[1].
I've seen smart chargers say 'we handle flat batteries 7.5V' which is no
use when the voltage drops below that.[2]

I would expect that mode to be a constant current mode, although they could
pulse or do other fancy things. But it should be able to deliver it
continuously without tripping out.

Requirement #2 is a display of voltage and current so I can see what's going
on. Little LEDs saying 'half' or 'full' do not cut it.

Nice-to-have #3 is a means of terminating charge when it's full, but I could
live without that.

Are there any 'smart' chargers that aren't also 'too clever for their own
good' chargers?

Thanks
Theo

[1] Instead I've been using a old 32V 2A bench PSU in constant current mode,
but 2A isn't very much and the case gets very hot (suspect a linear PSU).
It also isn't great to leave in the engine bay as it isn't weatherproofed in
any way.

[2] You might say the battery has had it by this point, but it's an AGM
battery in a hybrid so it lives an easy life. It only needs to provide 20A
for a few seconds to open contactors, it isn't used to start the car. I
might look at a LiFePO4 SLA-replacement next time.

Fit a switch for the boot bulb.

Could he rewire the boot light through the ignition circuit so there
is no need to remember to flip the switch?

Theo Wrote in message:
I think I might need a new car battery charger. However I'm failing to find
anything suitable and wonder if the team can recommend any models.

Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery. My
current 1980s dumb-charger can't handle delivering current into a low
voltage battery for more than a few seconds before the thermal trip goes[1].
I've seen smart chargers say 'we handle flat batteries 7.5V' which is no
use when the voltage drops below that.[2]

I would expect that mode to be a constant current mode, although they could
pulse or do other fancy things. But it should be able to deliver it
continuously without tripping out.

Requirement #2 is a display of voltage and current so I can see what's going
on. Little LEDs saying 'half' or 'full' do not cut it.

Nice-to-have #3 is a means of terminating charge when it's full, but I could
live without that.


Are there any 'smart' chargers that aren't also 'too clever for their own
good' chargers?

Thanks
Theo


[1] Instead I've been using a old 32V 2A bench PSU in constant current mode,
but 2A isn't very much and the case gets very hot (suspect a linear PSU).
It also isn't great to leave in the engine bay as it isn't weatherproofed in
any way.

[2] You might say the battery has had it by this point, but it's an AGM
battery in a hybrid so it lives an easy life. It only needs to provide 20A
for a few seconds to open contactors, it isn't used to start the car. I
might look at a LiFePO4 SLA-replacement next time.


Fit a switch for the boot bulb.
--
Jimk


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

Scott wrote:
Fit a switch for the boot bulb.

There's already two switches, one on the tailgate (which doesn't help if it
hasn't shut properly) and one on the bulb itself. But I leave the bulb on because
I want to see when I open the boot in the dark.

Could he rewire the boot light through the ignition circuit so there
is no need to remember to flip the switch?

I tend not to have the engine running when the boot is open.

I keep meaning to fit an LED, which will reduce the drain from 5W to 0.5W.
But it doesn't address the original question.

Theo

Theo Wrote in message:
Scott wrote:
Fit a switch for the boot bulb.

There's already two switches, one on the tailgate (which doesn't help if it
hasn't shut properly) and one on the bulb itself. But I leave the bulb on because
I want to see when I open the boot in the dark.

Could he rewire the boot light through the ignition circuit so there
is no need to remember to flip the switch?

I tend not to have the engine running when the boot is open.

I keep meaning to fit an LED, which will reduce the drain from 5W to 0.5W.
But it doesn't address the original question.

Theo


The real original question is "why does the boot light stay on
when it shouldn't?"

--
Jimk


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

Theo wrote:
I think I might need a new car battery charger. However I'm failing to find
anything suitable and wonder if the team can recommend any models.

Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery. My
current 1980s dumb-charger can't handle delivering current into a low
voltage battery for more than a few seconds before the thermal trip goes[1].
I've seen smart chargers say 'we handle flat batteries 7.5V' which is no
use when the voltage drops below that.[2]

I would expect that mode to be a constant current mode, although they could
pulse or do other fancy things. But it should be able to deliver it
continuously without tripping out.

Requirement #2 is a display of voltage and current so I can see what's going
on. Little LEDs saying 'half' or 'full' do not cut it.

Nice-to-have #3 is a means of terminating charge when it's full, but I could
live without that.


Are there any 'smart' chargers that aren't also 'too clever for their own
good' chargers?

Thanks
Theo


[1] Instead I've been using a old 32V 2A bench PSU in constant current mode,
but 2A isn't very much and the case gets very hot (suspect a linear PSU).
It also isn't great to leave in the engine bay as it isn't weatherproofed in
any way.

[2] You might say the battery has had it by this point, but it's an AGM
battery in a hybrid so it lives an easy life. It only needs to provide 20A
for a few seconds to open contactors, it isn't used to start the car. I
might look at a LiFePO4 SLA-replacement next time.


If you repeatedly €˜totally discharge your car battery, you will ruin it-
they arent designed to be totally discharged, and certainly not left in
that state.

You need to either find out why the boot isnt latching and fix it or at
least check it is closed correctly.

As for chargers, you may find one with meters etc but I expect it will be
expensive, unless it is an old (second hand) simple dumb charger. Modern
ones tend to have lcd or led displays and have smart charge capabilities.
Aldi and Lidl have them on offer every few months- each do versions of the
CTek (or Ctech?) charger which are pretty good. I have an Aldi one and I
bought my son in law a Lidl one. They are essentially the same, just
branded differently. Have a look on YouTube.

Neither have proper meters. They attempt to emulate a meter on the LCD.

They do charge very low batteries, the early ones didnt. There is a video
on YouTube covering this.



--
https://www.unitedway.org/our-impact...an-trafficking

On Tuesday, 21 July 2020 22:12:24 UTC+1, Theo wrote:
I think I might need a new car battery charger. However I'm failing to find
anything suitable and wonder if the team can recommend any models.

Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery. My
current 1980s dumb-charger can't handle delivering current into a low
voltage battery for more than a few seconds before the thermal trip goes[1].
I've seen smart chargers say 'we handle flat batteries 7.5V' which is no
use when the voltage drops below that.[2]

I would expect that mode to be a constant current mode, although they could
pulse or do other fancy things. But it should be able to deliver it
continuously without tripping out.

Requirement #2 is a display of voltage and current so I can see what's going
on. Little LEDs saying 'half' or 'full' do not cut it.

Nice-to-have #3 is a means of terminating charge when it's full, but I could
live without that.


Are there any 'smart' chargers that aren't also 'too clever for their own
good' chargers?

Thanks
Theo


[1] Instead I've been using a old 32V 2A bench PSU in constant current mode,
but 2A isn't very much and the case gets very hot (suspect a linear PSU).
It also isn't great to leave in the engine bay as it isn't weatherproofed in
any way.

[2] You might say the battery has had it by this point, but it's an AGM
battery in a hybrid so it lives an easy life. It only needs to provide 20A
for a few seconds to open contactors, it isn't used to start the car. I
might look at a LiFePO4 SLA-replacement next time.


I'd replace the light with an LED first.

Re chargers, if they're smart they won't charge a flat battery. It helps to understand why: checking a battery is connected & correctly polarised is a safety & liability issue, so they're never going to decide to skip that in today's world. Your only solution is a separate charger that can handle the initial charge to get it upto 10v or whatever the smart charger requires.

Ways to do that:
get an old dumb charger, plenty at car boots, most don't trip
- add a series 12v bulb to one that does trip
- live with your linear psu
- use a charging wallwart so it limits rather than trips
- initial charge from another lead acid

As said, repeated discharge will kill your lead acid very early.


NT

Theo wrote:
I think I might need a new car battery charger. However I'm failing to find
anything suitable and wonder if the team can recommend any models.

Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery. My
current 1980s dumb-charger can't handle delivering current into a low
voltage battery for more than a few seconds before the thermal trip goes[1].
I've seen smart chargers say 'we handle flat batteries 7.5V' which is no
use when the voltage drops below that.[2]

I would expect that mode to be a constant current mode, although they could
pulse or do other fancy things. But it should be able to deliver it
continuously without tripping out.

Requirement #2 is a display of voltage and current so I can see what's going
on. Little LEDs saying 'half' or 'full' do not cut it.

Nice-to-have #3 is a means of terminating charge when it's full, but I could
live without that.


Are there any 'smart' chargers that aren't also 'too clever for their own
good' chargers?

Thanks
Theo


[1] Instead I've been using a old 32V 2A bench PSU in constant current mode,
but 2A isn't very much and the case gets very hot (suspect a linear PSU).
It also isn't great to leave in the engine bay as it isn't weatherproofed in
any way.

[2] You might say the battery has had it by this point, but it's an AGM
battery in a hybrid so it lives an easy life. It only needs to provide 20A
for a few seconds to open contactors, it isn't used to start the car. I
might look at a LiFePO4 SLA-replacement next time.

There were two switches in the trunk of my previous car.

A three position slide switch. A trunk-closed switch.

The three position switch had:

Always ON
Gated by trunk-closed switch
Always OFF

as the three positions. If you wanted to lock an elf in the
trunk and have the light ON, you could do that.

You should check and make sure your "option" switch is set
in the best position.

One of my door switches on the old car was
intermittent, but, the system is normally open,
and the intermittent switch means it doesn't
come on when the door is open. Fiddling with the
switch would bring it on. Closing the door always
turned if off. Just ON was a problem. Again, the courtesy
light had control switch had:

Always ON
Gated by door switch(es) - wired OR
Always OFF

I would work on my vampire loads, before giving in
to the appetites of the car.

My current car has vampire loads of less than 20mA.
The meter I used, can't give readings better than that
(that's the clamp-on ammeter reading). I would need
leads with banana plugs on the end, to be making a current
measurement without disturbing the electrical system.

My charger has no problem handling the 20mA vampire load.
And, it automatically cycles when the Vbatt drops low
enough. The only thing my charger doesn't do, is there
is no temperature compensation. The voltages it uses,
correspond to operation at 25C. If the air temperature
was somewhat different, the battery would be under-charged
or over-charged accordingly. There is a least one
commercial charger, where the "temperature measurement lead"
is a separate item, and you can place the lead where ever
seems appropriate.

If you change battery chemistries, then it's possible
some charger details will change too.

Paul

On Tue, 21 Jul 2020 22:12:20 +0100, Theo wrote:

I think I might need a new car battery charger. However I'm failing to
find anything suitable and wonder if the team can recommend any models.

Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little
light on - which if you don't drive for a week or two empties the
battery. My current 1980s dumb-charger can't handle delivering current
into a low voltage battery for more than a few seconds before the
thermal trip goes[1].
I've seen smart chargers say 'we handle flat batteries 7.5V' which is
no use when the voltage drops below that.[2]

I would expect that mode to be a constant current mode, although they
could pulse or do other fancy things. But it should be able to deliver
it continuously without tripping out.

Requirement #2 is a display of voltage and current so I can see what's
going on. Little LEDs saying 'half' or 'full' do not cut it.

Nice-to-have #3 is a means of terminating charge when it's full, but I
could live without that.


Are there any 'smart' chargers that aren't also 'too clever for their
own good' chargers?

Thanks Theo


[1] Instead I've been using a old 32V 2A bench PSU in constant current
mode,
but 2A isn't very much and the case gets very hot (suspect a linear
PSU). It also isn't great to leave in the engine bay as it isn't
weatherproofed in any way.

[2] You might say the battery has had it by this point, but it's an AGM
battery in a hybrid so it lives an easy life. It only needs to provide
20A for a few seconds to open contactors, it isn't used to start the
car. I might look at a LiFePO4 SLA-replacement next time.

I used an old 19v x 4A laptop power supply with a couple of 55W headlight
bulbs in series to charge my flat battery. It started at 2.5 amps and
dropped to 1.8 amps over a couple of days, giving a full charge.

On 21/07/2020 22:12, Theo wrote:
I think I might need a new car battery charger. However I'm failing to find
anything suitable and wonder if the team can recommend any models.

Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery. My
current 1980s dumb-charger can't handle delivering current into a low
voltage battery for more than a few seconds before the thermal trip goes[1].
I've seen smart chargers say 'we handle flat batteries 7.5V' which is no
use when the voltage drops below that.[2]

I would expect that mode to be a constant current mode, although they could
pulse or do other fancy things. But it should be able to deliver it
continuously without tripping out.

Requirement #2 is a display of voltage and current so I can see what's going
on. Little LEDs saying 'half' or 'full' do not cut it.

Nice-to-have #3 is a means of terminating charge when it's full, but I could
live without that.


Are there any 'smart' chargers that aren't also 'too clever for their own
good' chargers?

Thanks
Theo


[1] Instead I've been using a old 32V 2A bench PSU in constant current mode,
but 2A isn't very much and the case gets very hot (suspect a linear PSU).
It also isn't great to leave in the engine bay as it isn't weatherproofed in
any way.

[2] You might say the battery has had it by this point, but it's an AGM
battery in a hybrid so it lives an easy life. It only needs to provide 20A
for a few seconds to open contactors, it isn't used to start the car. I
might look at a LiFePO4 SLA-replacement next time.

On #1, I have lead acid batteries for lights and electric fencers in a
stable block. These are usually ex-car ones, so often a bit tired, and
they do sometimes get run right down. I often need to start them off
using an ancient transformer type with a moving iron ammeter. If you
don't have one of these, look out in car boot sales.

I also have an older version of one of these

https://www.machinemart.co.uk/p/clar...ngine-starter/

Mine has a transformer and I think this is likely to have one too.
Occasionally handy as it will run off a small genny.

Brian Reay explained on 21/07/2020 :
As for chargers, you may find one with meters etc but I expect it will be
expensive, unless it is an old (second hand) simple dumb charger. Modern
ones tend to have lcd or led displays and have smart charge capabilities.
Aldi and Lidl have them on offer every few months- each do versions of the
CTek (or Ctech?) charger which are pretty good. I have an Aldi one and I
bought my son in law a Lidl one. They are essentially the same, just
branded differently. Have a look on YouTube.

The Lidl one is suggested to be better built than the Aldi version.


Neither have proper meters. They attempt to emulate a meter on the LCD.

Which is fine, there is no need for current measurement, as with old
fashioned dumb chargers - the charger takes care of current.

They do charge very low batteries, the early ones didnt. There is a video
on YouTube covering this.

I didn't know that, until years after I bought it, I watched the video.
I thought the flashing display simply meant it was unable to attempt to
charge (I never read instructions).

The older smart chargers, the only way to get them to charge was to
initially parallel the flat battery with a charged one.

I agree it is just plain daft, not to fix the discharge/ the boot light
left on. It is a great way to quickly wreck a battery and so easy to
fix. Modern cars turn their interior lights off, if the car is left
undisturbed for a while. Leave my car's door open for 20 minutes
without otherwise disturbing the car and the interior lights go off.
I going a stage further - I ordered myself a fancy micro-based battery
analyser last week, due for delivery today. I have quite a few
batteries around the place and battery capabilities are notoriously
difficult to assess effectively.

Paul presented the following explanation :
My current car has vampire loads of less than 20mA.
The meter I used, can't give readings better than that
(that's the clamp-on ammeter reading). I would need
leads with banana plugs on the end, to be making a current
measurement without disturbing the electrical system.

With my car it is easy to test discharge whilst parked. There is a
copper link/busbar linking end of battery lead to the under bonnet fuse
panel, which has all the very large main fuses in it. I just connect mA
meter between battery +ve post and fuse end of bus bar and remove the
link. The measurement will not include any discharge via starter motor,
or alternator, but those are much less likely self discharge culprits.

On 21 Jul 2020 22:55:15 +0100 (BST), Theo
wrote:

Scott wrote:
Fit a switch for the boot bulb.

There's already two switches, one on the tailgate (which doesn't help if it
hasn't shut properly) and one on the bulb itself. But I leave the bulb on because
I want to see when I open the boot in the dark.

Could he rewire the boot light through the ignition circuit so there
is no need to remember to flip the switch?

I tend not to have the engine running when the boot is open.

I keep meaning to fit an LED, which will reduce the drain from 5W to 0.5W.
But it doesn't address the original question.

What about a time delay switch? Could you get one that cuts off after
(say) 2 minutes?

With respect, I think the original question is the wrong question :-)
Surely the correct question is how to find the best solution to the
problem.

To build one is not that hard though a beefy bridge rectifier and a
transformer salvaged from some high power low voltage device, probably find
something at a boot sale.
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Theo" wrote in message
...
I think I might need a new car battery charger. However I'm failing to
find
anything suitable and wonder if the team can recommend any models.

Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery. My
current 1980s dumb-charger can't handle delivering current into a low
voltage battery for more than a few seconds before the thermal trip
goes[1].
I've seen smart chargers say 'we handle flat batteries 7.5V' which is no
use when the voltage drops below that.[2]

I would expect that mode to be a constant current mode, although they
could
pulse or do other fancy things. But it should be able to deliver it
continuously without tripping out.

Requirement #2 is a display of voltage and current so I can see what's
going
on. Little LEDs saying 'half' or 'full' do not cut it.

Nice-to-have #3 is a means of terminating charge when it's full, but I
could
live without that.


Are there any 'smart' chargers that aren't also 'too clever for their own
good' chargers?

Thanks
Theo


[1] Instead I've been using a old 32V 2A bench PSU in constant current
mode,
but 2A isn't very much and the case gets very hot (suspect a linear PSU).
It also isn't great to leave in the engine bay as it isn't weatherproofed
in
any way.

[2] You might say the battery has had it by this point, but it's an AGM
battery in a hybrid so it lives an easy life. It only needs to provide
20A
for a few seconds to open contactors, it isn't used to start the car. I
might look at a LiFePO4 SLA-replacement next time.

In article ,
Theo wrote:
I think I might need a new car battery charger. However I'm failing to find
anything suitable and wonder if the team can recommend any models.

Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery. My
current 1980s dumb-charger can't handle delivering current into a low
voltage battery for more than a few seconds before the thermal trip goes[1].
I've seen smart chargers say 'we handle flat batteries 7.5V' which is no
use when the voltage drops below that.[2]

Most modern chargers won't work with a totally flat battery. They use
battery volts to pull in the reverse connection protection relay. So you
may need to use a jump battery to get it started. Other than that, most
will limit the current demanded to what they can deliver.

--
*Why is the man who invests all your money called a broker? *

Dave Plowman London SW
To e-mail, change noise into sound.

Scott wrote:
What about a time delay switch? Could you get one that cuts off after
(say) 2 minutes?

Having taken the thing apart, it turns out the bulb holder is actually part
of the switch mechanism, and one end of the bulb moves up or down when you
flip the switch.

So mechanically it's a bit tricky, but I think I can do something with:

- intentionally blow the bulb, so I have the glass envelope to use as a
substrate

- fit some white LEDs and a resistor across it. The LEDs are chosen such
that the forward voltage is set to match say the '25% battery' voltage
(looks like 12.0V). When the battery voltage falls below that level the LED
current collapses and the load naturally falls away.

It would need some tweaking to get the current curve right, and it's
possible a more sensitve cutoff circuit would be needed. Worth a try
though.

With respect, I think the original question is the wrong question :-)
Surely the correct question is how to find the best solution to the
problem.

Well indeed, but 'I wouldn't start from the bottom of a hole' is not an
answer to a question about the best set of grappling irons.

Theo

On 22 Jul 2020 11:59:16 +0100 (BST), Theo wrote:

- fit some white LEDs and a resistor across it. The LEDs are chosen
such that the forward voltage is set to match say the '25% battery'
voltage (looks like 12.0V). When the battery voltage falls below that
level the LED current collapses and the load naturally falls away.

Apart from that through the resistor across the LED and modern white
LEDS take naff all current. You can get LED versions of pretty well
any automotive bulb that is out there apart from some headlight
bulbs. You'd not want ones that are compatible with some cars "bulb
failure" systems as they have resistors to ensure they draw enough
current to supress the "bulb failure" warning.

The correct solution is to work out what stops the boot from not
closing properly and fix that. Bit of lubrication? Small adjustment
to the pin that the lock striker engages with? Still if trying to
develop a complicated workaround, ignoring the root cause, keeps some
one happy...

--
Cheers
Dave.

On 22/07/2020 12:13, Dave Liquorice wrote:
On 22 Jul 2020 11:59:16 +0100 (BST), Theo wrote:

- fit some white LEDs and a resistor across it. The LEDs are chosen
such that the forward voltage is set to match say the '25% battery'
voltage (looks like 12.0V). When the battery voltage falls below that
level the LED current collapses and the load naturally falls away.

Apart from that through the resistor across the LED and modern white
LEDS take naff all current. You can get LED versions of pretty well
any automotive bulb that is out there apart from some headlight
bulbs. You'd not want ones that are compatible with some cars "bulb
failure" systems as they have resistors to ensure they draw enough
current to supress the "bulb failure" warning.

The correct solution is to work out what stops the boot from not
closing properly and fix that. Bit of lubrication? Small adjustment
to the pin that the lock striker engages with? Still if trying to
develop a complicated workaround, ignoring the root cause, keeps some
one happy...

a car is not the place for LED lights....

Dave Liquorice wrote:
On 22 Jul 2020 11:59:16 +0100 (BST), Theo wrote:

- fit some white LEDs and a resistor across it. The LEDs are chosen
such that the forward voltage is set to match say the '25% battery'
voltage (looks like 12.0V). When the battery voltage falls below that
level the LED current collapses and the load naturally falls away.

Apart from that through the resistor across the LED and modern white
LEDS take naff all current. You can get LED versions of pretty well
any automotive bulb that is out there apart from some headlight
bulbs. You'd not want ones that are compatible with some cars "bulb
failure" systems as they have resistors to ensure they draw enough
current to supress the "bulb failure" warning.

In this case the circuit is carefully designed to be sensitive to voltage.
A regular automotive indicator LED bulb is a 3.2V white LED and a series
resistor which drops about 10V. The resistor limits the current so the
forward voltage of the LED is immaterial. In my setup the current is very
much dependent on the forward voltage, which is the point.

I'm not sure I'd be able to find LEDs when put in series with quite the
right voltage/current curve though. It might need a more conventional
cutoff circuit.

The correct solution is to work out what stops the boot from not
closing properly and fix that. Bit of lubrication? Small adjustment
to the pin that the lock striker engages with? Still if trying to
develop a complicated workaround, ignoring the root cause, keeps some
one happy...

In this particular case, a load of cardboard fouling the lid.
Root cause analysis doesn't help when the root cause is the idiot user.
Upgrades to the idiot may be unsuccessful.

Theo

On Wed, 22 Jul 2020 11:25:26 +0100, "Dave Plowman (News)"
wrote:

In article ,
Theo wrote:
I think I might need a new car battery charger. However I'm failing to find
anything suitable and wonder if the team can recommend any models.

Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery. My
current 1980s dumb-charger can't handle delivering current into a low
voltage battery for more than a few seconds before the thermal trip goes[1].
I've seen smart chargers say 'we handle flat batteries 7.5V' which is no
use when the voltage drops below that.[2]

Most modern chargers won't work with a totally flat battery. They use
battery volts to pull in the reverse connection protection relay. So you
may need to use a jump battery to get it started. Other than that, most
will limit the current demanded to what they can deliver.

I cannot imagine any of this is good for the battery. It seems to me
a destructive way of solving a minor issue.

On 21/07/2020 22:12, Theo wrote:

Requirement #2 is a display of voltage and current so I can see what's going
on. Little LEDs saying 'half' or 'full' do not cut it.

A voltage reading on a battery that's under charge tells you very little
about the battery. It tells you a bit about the charger, that's all.

Bill

On 21 Jul 2020 22:12:20 +0100 (BST), Theo
wrote:

I think I might need a new car battery charger. However I'm failing to find
anything suitable and wonder if the team can recommend any models.

Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery.

Angle grinder to remove the boot lid, duct tape to insulate the bare cables.

Even buying both new should work out cheaper than a new battery charger.

Or fix / replace the switch

--

On 21/07/2020 22:12, Theo wrote:
Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery.

Fit a little intermittent bleeper across the boot light. Easy and cheap.

Bill

In article ,
Scott wrote:
On Wed, 22 Jul 2020 11:25:26 +0100, "Dave Plowman (News)"
wrote:

In article ,
Theo wrote:
I think I might need a new car battery charger. However I'm failing to find
anything suitable and wonder if the team can recommend any models.

Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery. My
current 1980s dumb-charger can't handle delivering current into a low
voltage battery for more than a few seconds before the thermal trip goes[1].
I've seen smart chargers say 'we handle flat batteries 7.5V' which is no
use when the voltage drops below that.[2]

Most modern chargers won't work with a totally flat battery. They use
battery volts to pull in the reverse connection protection relay. So you
may need to use a jump battery to get it started. Other than that, most
will limit the current demanded to what they can deliver.

I cannot imagine any of this is good for the battery. It seems to me
a destructive way of solving a minor issue.

If the battery is totally flat it will be damaged anyway. With such an
expensive item best to charge it long before it is flat.

--
*Jokes about German sausage are the wurst.*

Dave Plowman London SW
To e-mail, change noise into sound.

On Wed, 22 Jul 2020 14:56:04 +0100, "Dave Plowman (News)"
wrote:

In article ,
Scott wrote:
On Wed, 22 Jul 2020 11:25:26 +0100, "Dave Plowman (News)"
wrote:

In article ,
Theo wrote:
I think I might need a new car battery charger. However I'm failing to find
anything suitable and wonder if the team can recommend any models.

Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery. My
current 1980s dumb-charger can't handle delivering current into a low
voltage battery for more than a few seconds before the thermal trip goes[1].
I've seen smart chargers say 'we handle flat batteries 7.5V' which is no
use when the voltage drops below that.[2]

Most modern chargers won't work with a totally flat battery. They use
battery volts to pull in the reverse connection protection relay. So you
may need to use a jump battery to get it started. Other than that, most
will limit the current demanded to what they can deliver.

I cannot imagine any of this is good for the battery. It seems to me
a destructive way of solving a minor issue.

If the battery is totally flat it will be damaged anyway. With such an
expensive item best to charge it long before it is flat.

True, but OP must be planning to flatten the next battery as well
(otherwise he wouldn't need the charger).

In article ,
Scott wrote:
If the battery is totally flat it will be damaged anyway. With such an
expensive item best to charge it long before it is flat.

True, but OP must be planning to flatten the next battery as well
(otherwise he wouldn't need the charger).

You use the charger before the battery is flat?

--
*Eschew obfuscation *

Dave Plowman London SW
To e-mail, change noise into sound.

On Wed, 22 Jul 2020 15:44:29 +0100, "Dave Plowman (News)"
wrote:

In article ,
Scott wrote:
If the battery is totally flat it will be damaged anyway. With such an
expensive item best to charge it long before it is flat.

True, but OP must be planning to flatten the next battery as well
(otherwise he wouldn't need the charger).

You use the charger before the battery is flat?

An ordinary charger can do this, surely?

My understanding is that OP is looking for a special charger that can
recharge flat battery (.Requirement #1 is to be able to charge flat
batteries').

Theo presented the following explanation :
In this case the circuit is carefully designed to be sensitive to voltage.
A regular automotive indicator LED bulb is a 3.2V white LED and a series
resistor which drops about 10V. The resistor limits the current so the
forward voltage of the LED is immaterial. In my setup the current is very
much dependent on the forward voltage, which is the point.

I'm not sure I'd be able to find LEDs when put in series with quite the
right voltage/current curve though. It might need a more conventional
cutoff circuit.

I doubt that will work, LED's dim appreciable as the voltage reduces,
so they have no clear cut off voltage. The only way to get it to work
is to have the LED's very dim at full voltage, too dim to be useful.

williamwright pretended :
A voltage reading on a battery that's under charge tells you very little
about the battery. It tells you a bit about the charger, that's all.

With a current limited charger, it does tell you how the recharge is
progressing.

On Wednesday, 22 July 2020 11:59:20 UTC+1, Theo wrote:
Scott wrote:
What about a time delay switch? Could you get one that cuts off after
(say) 2 minutes?

Having taken the thing apart, it turns out the bulb holder is actually part
of the switch mechanism, and one end of the bulb moves up or down when you
flip the switch.

So mechanically it's a bit tricky, but I think I can do something with:

- intentionally blow the bulb, so I have the glass envelope to use as a
substrate

- fit some white LEDs and a resistor across it. The LEDs are chosen such
that the forward voltage is set to match say the '25% battery' voltage
(looks like 12.0V). When the battery voltage falls below that level the LED
current collapses and the load naturally falls away.

It would need some tweaking to get the current curve right, and it's
possible a more sensitve cutoff circuit would be needed. Worth a try
though.

that's a crappy option, but it would sorta work & is simple. LED i will vary from max at car charging down to zero at 12v.


NT

williamwright wrote:
On 21/07/2020 22:12, Theo wrote:
Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery.

Fit a little intermittent bleeper across the boot light. Easy and cheap.

I like it

Theo

jon wrote:
I used an old 19v x 4A laptop power supply with a couple of 55W headlight
bulbs in series to charge my flat battery. It started at 2.5 amps and
dropped to 1.8 amps over a couple of days, giving a full charge.

That's a handy idea. I have some 12V 20A PSUs, and a headlight bulb in
series would limit the initial current to 4.5A which would be sensible.
That would be enough to get it off the floor, and then a regular charger can
take over. It wouldn't be the fastest but it would be good enough to begin
with.

Theo

On 22/07/2020 17:08, Harry Bloomfield wrote:
williamwright pretended :
A voltage reading on a battery that's under charge tells you very
little about the battery. It tells you a bit about the charger, that's
all.

With a current limited charger, it does tell you how the recharge is
progressing.

Yes.

Bill

On 22/07/2020 22:48, Theo wrote:
williamwright wrote:
On 21/07/2020 22:12, Theo wrote:
Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery.

Fit a little intermittent bleeper across the boot light. Easy and cheap.

I like it

Theo

I had to put a bleeper across my indicators in one van I had because the
engine was so loud I couldn't hear the tick-tock thing.

Bill

williamwright wrote:
On 22/07/2020 22:48, Theo wrote:
williamwright wrote:
On 21/07/2020 22:12, Theo wrote:
Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery.

Fit a little intermittent bleeper across the boot light. Easy and cheap.

I like it

Theo

I had to put a bleeper across my indicators in one van I had because the
engine was so loud I couldn't hear the tick-tock thing.

Bill


Our familys first Renault 4 had non-self cancelling indicators and we
fitted a bleeper for similar reasons.

Tim

--
Please don't feed the trolls

Theo brought next idea :
That's a handy idea. I have some 12V 20A PSUs, and a headlight bulb in
series would limit the initial current to 4.5A which would be sensible.
That would be enough to get it off the floor, and then a regular charger can
take over. It wouldn't be the fastest but it would be good enough to begin
with.

12.0v will not put any charge at all into a lead acid battery. Even
13.8v is only capable of bring a battery up to a 50% charge.

On 21/07/2020 22:12, Theo wrote:
I think I might need a new car battery charger. However I'm failing to find
anything suitable and wonder if the team can recommend any models.

Requirement #1 is to be able to charge flat batteries.
My boot lid sometimes doesn't latch properly and leaves a dim little light
on - which if you don't drive for a week or two empties the battery. My
current 1980s dumb-charger can't handle delivering current into a low
voltage battery for more than a few seconds before the thermal trip goes[1].
I've seen smart chargers say 'we handle flat batteries 7.5V' which is no
use when the voltage drops below that.[2]

A high wattage resistor to limit the current flow when the battery
terminal voltage is very low would solve your problem. Assuming a rough
16v output and a 9v under initial charge you will need to drop about 7v
and at say 4A so a 50W rated 2 ohm resistor ought to cope. Or perhaps
better a string of two 15W 1 ohm resistors so that you can up the
current by clipping on up the chain or use them in parallel as it gains
voltage. That way you don't overload your charger but you do end up with
some pretty warm resistors dissipating the excess power as heat.

I would expect that mode to be a constant current mode, although they could
pulse or do other fancy things. But it should be able to deliver it
continuously without tripping out.

A voltage in series with a suitably rated current limiting resistor will
do - you don't really care about efficiency here.

Requirement #2 is a display of voltage and current so I can see what's going
on. Little LEDs saying 'half' or 'full' do not cut it.

DVM in series if you must.

Nice-to-have #3 is a means of terminating charge when it's full, but I could
live without that.


Are there any 'smart' chargers that aren't also 'too clever for their own
good' chargers?

Not really. Any smart charger will take one look at your battery and
decide that it is a Norwegian blue parrot analogue. Stone dead.

Lead acid batteries that have been to such low terminal voltages usually
have at least one weak cell in the chain that is essentially wrecked.

[1] Instead I've been using a old 32V 2A bench PSU in constant current mode,
but 2A isn't very much and the case gets very hot (suspect a linear PSU).
It also isn't great to leave in the engine bay as it isn't weatherproofed in
any way.

[2] You might say the battery has had it by this point, but it's an AGM
battery in a hybrid so it lives an easy life. It only needs to provide 20A
for a few seconds to open contactors, it isn't used to start the car. I
might look at a LiFePO4 SLA-replacement next time.

Swap the incandescent light for an LED and you will give yourself
another marginal factor of 10 safety factor on wrecking it.

--
Regards,
Martin Brown

On 22/07/2020 22:57, Theo wrote:
jon wrote:
I used an old 19v x 4A laptop power supply with a couple of 55W headlight
bulbs in series to charge my flat battery. It started at 2.5 amps and
dropped to 1.8 amps over a couple of days, giving a full charge.

That's a handy idea. I have some 12V 20A PSUs, and a headlight bulb in
series would limit the initial current to 4.5A which would be sensible.
That would be enough to get it off the floor, and then a regular charger can
take over. It wouldn't be the fastest but it would be good enough to begin
with.

12v is nowhere near enough to make the lead acid battery charge. A lead
acid charger needs to source at least 14v (usually about 17v no load).

Putting the headlamp in series with your existing dumb charger will
probably solve the problem by stopping it overheating. You might
actually need to find a 6v 20W filament bulb to match the voltage drop.

--
Regards,
Martin Brown

Martin Brown wrote:
On 22/07/2020 22:57, Theo wrote:
jon wrote:
I used an old 19v x 4A laptop power supply with a couple of 55W
headlight
bulbs in series to charge my flat battery. It started at 2.5 amps and
dropped to 1.8 amps over a couple of days, giving a full charge.

That's a handy idea. I have some 12V 20A PSUs, and a headlight bulb in
series would limit the initial current to 4.5A which would be sensible.
That would be enough to get it off the floor, and then a regular
charger can
take over. It wouldn't be the fastest but it would be good enough to
begin
with.

12v is nowhere near enough to make the lead acid battery charge. A lead
acid charger needs to source at least 14v (usually about 17v no load).

Putting the headlamp in series with your existing dumb charger will
probably solve the problem by stopping it overheating. You might
actually need to find a 6v 20W filament bulb to match the voltage drop.


He's bringing it off the floor though.

Not doing a complete charge cycle with this bodge charger.

Just lifting the battery high enough, so a
standard charger will accept the battery
and finish the job.

If the battery is 60Ah, and that part of the knee
of the charging curve is 10% of that, or about 6Ah,
you can figure out how long it'll take to get that
far up the curve. And as long as the voltage
is slightly greater than the battery state of charge,
it'll charge. That's because coulombs are going into
the battery, and "something gotta give". Now, if
you applied X volts, and no current flowed, *then*
I would agree that no chemical state change could
occur. But if the coulombs are going in there,
some redox reaction is bound to be working with
that as a reactant.

And for a damaged battery, the battery is no longer
"stiff", and the terminal voltage will shoot up
rather quickly. I've had several batteries on
my dumb charger, where the stupid thing says the
battery is full, 30 seconds after a charge starts.
And it's because the battery is up around 16V, instead
of resisting the charging effort and measuring 11.6V.
And with the dumb charger, the charger only pushes
a bit less than an ampere, at 16V. So you're not
really charging the battery all that fast any more
either. This is why non-CC chargers "suck". And why
the SMPS ones are better (consistent charging over
time through the charge cycle - no goofy corner
cases).

Paul

Paul wrote:
He's bringing it off the floor though.

Not doing a complete charge cycle with this bodge charger.

Just lifting the battery high enough, so a
standard charger will accept the battery
and finish the job.

Indeed, and that's part of the attraction of this 'redneck charger':

- the supply is 12V so at no time will it ever overcharge a battery

- if the terminal voltage is low and the battery accepts current, the lamp
will light. The lamp prevents overcurrent.

- as the terminal voltage rises the lamp will dim. The lamp is a (very non
linear) indicator of the current and thus the terminal voltage

- if the terminal voltage shoots up (because the battery is knackered) the
lamp will light briefly and then fade out

- because it won't overcharge it's safe to leave it on for a long period.
In the end case the 12V out and 12V battery voltage balance and no current
flows. That's roughly the 25% SoC condition so the battery is within
nominal limits at this point.

- once it's reached 12V it's safe to apply a 'normal' charger (or in this case
leave the car powered up and it'll charge it from the traction battery,
starting the engine when that needs topping up)


It would probably need a bit of tinkering to get the right bulb to cover all
the conditions though. Probably a voltmeter is still useful as a better
indicator than the lamp itself.

Theo