I have a power tool (chainsaw) which is used on site at night where
noise is a problem. It uses a lithium ion battery of 36V 3Ah which
lasts about 20 minutes of use. The 330W 240v charger takes about 1/2
hour. I have 3 batteries which is fine many nights but could do with
charging them from a DC power source like a series of lead acid
leisure batteries, would this be feasible? Starting a generator
defeats the object and an inverter off a vehicle battery ( we have
welfare units with isolated 12V battery) would need 27 Amps even if it
were loss less.

AJH

wrote:
I have a power tool (chainsaw) which is used on site at night where
noise is a problem. It uses a lithium ion battery of 36V 3Ah which
lasts about 20 minutes of use. The 330W 240v charger takes about 1/2
hour. I have 3 batteries which is fine many nights but could do with
charging them from a DC power source like a series of lead acid
leisure batteries, would this be feasible? Starting a generator
defeats the object and an inverter off a vehicle battery ( we have
welfare units with isolated 12V battery) would need 27 Amps even if it
were loss less.

AJH


Would it be feasible to power the saw from three 12V 15Ah deep discharge
batteries, via a short cable? Obviously if you are working up a tree the
answer would be no.
I had a problem a few years ago where we had to work in some long and
rather labyrinthine unlit voids (think sewer tunnels but without the
sewage; can't saw more than that). We only realised the problem once we
were on site (had been told that the lighting worked) so we used
caplamps for a day, then I rigged up an array of 12V 10W halogens on a
heavy photographic tripod and powered them from a 30Ah deep discharge
battery. I had a good long cable so it was only necessary to move the
battery (which was on a trolley with the tools and equipment) every now
and then.
Incidentally, years ago a communal TV system installer of my
acquaintance used to tap into the 55VAC line power carried on the
distribution trunks to feed a 24V headlamp bulb (the connection being
to the non-common terminals, so the two filaments were in series.)
Frankly I thought it was more trouble than it was worth!

Bill

In article ,
writes:
I have a power tool (chainsaw) which is used on site at night where
noise is a problem. It uses a lithium ion battery of 36V 3Ah which
lasts about 20 minutes of use. The 330W 240v charger takes about 1/2
hour. I have 3 batteries which is fine many nights but could do with
charging them from a DC power source like a series of lead acid
leisure batteries, would this be feasible? Starting a generator
defeats the object and an inverter off a vehicle battery ( we have
welfare units with isolated 12V battery) would need 27 Amps even if it
were loss less.

It's not easy. You need a supply which has a very precisely set voltage
and current limit, the value of which depend on the particular Li Ion
batterry. If you are fast charging them, it's also essential to monitor
the temperature. Also you must take them off charge when the charge is
completed.

The really nasty part is that if you get this a little bit wrong, the
battery is liable to explode into flames like a firework (and like a
firework, you can't put it out with a fire extinguisher, although that
might be useful to put out whatever else it ignites). There are videos
on youtube.

So unless you have a good quality electronics bench supply with accurate
voltage setting (to 0.1V) and current limiting, it's not safe to do so.

I have done it with a mobile phone battery - doing it with something
bigger has bigger risks.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 10/11/2013 20:38, wrote:
I have a power tool (chainsaw) which is used on site at night where
noise is a problem. It uses a lithium ion battery of 36V 3Ah which
lasts about 20 minutes of use. The 330W 240v charger takes about 1/2
hour. I have 3 batteries which is fine many nights but could do with
charging them from a DC power source like a series of lead acid
leisure batteries, would this be feasible? Starting a generator
defeats the object and an inverter off a vehicle battery ( we have
welfare units with isolated 12V battery) would need 27 Amps even if it
were loss less.

AJH


Inverters are pretty efficient, somewhere around 85% IIRC, so this is
probably going to be the easiest & safest way to do it, what is the
problem with taking 27+ amps from a leisure battery, the total drain on
the battery will be roughly the same with a slower charger anyway?

As I understand it, when you charge a Li Ion, it is charged at high
current for the first half of the charge cycle, then the current drops
off, so your 330w charger probably won't be drawing the full 330w from
start to finish anyway.

Granted, the efficiency will be better with a DC/DC solution, but I
don't expect it will make an appreciable difference, especially if you
can recharge the leisure battery during the following day anyway.

--
Toby...
Remove your pants to reply

On Sun, 10 Nov 2013 21:07:28 +0000 (UTC),
(Andrew Gabriel) wrote:

In article ,
writes:
I have a power tool (chainsaw) which is used on site at night where
noise is a problem. It uses a lithium ion battery of 36V 3Ah which
lasts about 20 minutes of use. The 330W 240v charger takes about 1/2
hour. I have 3 batteries which is fine many nights but could do with
charging them from a DC power source like a series of lead acid
leisure batteries, would this be feasible? Starting a generator
defeats the object and an inverter off a vehicle battery ( we have
welfare units with isolated 12V battery) would need 27 Amps even if it
were loss less.

It's not easy. You need a supply which has a very precisely set voltage
and current limit, the value of which depend on the particular Li Ion
batterry. If you are fast charging them, it's also essential to monitor
the temperature. Also you must take them off charge when the charge is
completed.

The really nasty part is that if you get this a little bit wrong, the
battery is liable to explode into flames like a firework (and like a
firework, you can't put it out with a fire extinguisher, although that
might be useful to put out whatever else it ignites). There are videos
on youtube.

So unless you have a good quality electronics bench supply with accurate
voltage setting (to 0.1V) and current limiting, it's not safe to do so.

I have done it with a mobile phone battery - doing it with something
bigger has bigger risks.

Three fully charged lead acid car batteries? Probably cheaper than the
lithiums but the downside is the need for a cable and some means of
attaching it to the tool.

A H&S problem I would assume if you trail a cable to such a tool?

How long can a chainsaw be used for incidentally, a Duracell PP3 might
have enough juice to send some hi vis spotters into white finger mode.

AB

On Sun, 10 Nov 2013 22:09:21 +0000, Toby
wrote:


Inverters are pretty efficient, somewhere around 85% IIRC, so this is
probably going to be the easiest & safest way to do it,

Yes from the replies I think so, the total charge is only 108Wh so a
largish inverter hard wired to the second, split charged, battery in
the vehicle seems the route to go.

AJH

On 10/11/13 20:38, wrote:
I have a power tool (chainsaw) which is used on site at night where
noise is a problem. It uses a lithium ion battery of 36V 3Ah which
lasts about 20 minutes of use. The 330W 240v charger takes about 1/2
hour. I have 3 batteries which is fine many nights but could do with
charging them from a DC power source like a series of lead acid
leisure batteries, would this be feasible? Starting a generator
defeats the object and an inverter off a vehicle battery ( we have
welfare units with isolated 12V battery) would need 27 Amps even if it
were loss less.


You can get model (aircraft/boat/car) charger which will do thus BUT
they are designed to hook onto the raw battery itself, and not expecting
any protection **** on the way.

You might do better with a 12v inverter

AJH



--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

The Natural Philosopher wrote:
On 10/11/13 20:38, wrote:
I have a power tool (chainsaw) which is used on site at night where
noise is a problem. It uses a lithium ion battery of 36V 3Ah which
lasts about 20 minutes of use. The 330W 240v charger takes about 1/2
hour. I have 3 batteries which is fine many nights but could do with
charging them from a DC power source like a series of lead acid
leisure batteries, would this be feasible? Starting a generator
defeats the object and an inverter off a vehicle battery ( we have
welfare units with isolated 12V battery) would need 27 Amps even if it
were loss less.


You can get model (aircraft/boat/car) charger which will do thus BUT
they are designed to hook onto the raw battery itself, and not expecting
any protection **** on the way.

You might do better with a 12v inverter

AJH



If the charger is supplied from a power pack (wallwart in American)which
supplies 12v dc to the charger then it should be easy to use the proper
charger

The Natural Philosopher wrote:

On 10/11/13 20:38, wrote:

I have a power tool (chainsaw) which is used on site at night
where noise is a problem. It uses a lithium ion battery of 36V 3Ah
which lasts about 20 minutes of use. I have 3 batteries which is
fine many nights

You might do better with a 12v inverter

Might just do better with a few more batteries ...

On 10/11/2013 21:07, Andrew Gabriel wrote:
In article ,
writes:
I have a power tool (chainsaw) which is used on site at night where
noise is a problem. It uses a lithium ion battery of 36V 3Ah which
lasts about 20 minutes of use. The 330W 240v charger takes about 1/2
hour. I have 3 batteries which is fine many nights but could do with
charging them from a DC power source like a series of lead acid
leisure batteries, would this be feasible? Starting a generator
defeats the object and an inverter off a vehicle battery ( we have
welfare units with isolated 12V battery) would need 27 Amps even if it
were loss less.

It's not easy. You need a supply which has a very precisely set voltage
and current limit, the value of which depend on the particular Li Ion
batterry. If you are fast charging them, it's also essential to monitor
the temperature. Also you must take them off charge when the charge is
completed.

They are as Boeing will testify seriously inclined to self immolation.

The really nasty part is that if you get this a little bit wrong, the
battery is liable to explode into flames like a firework (and like a
firework, you can't put it out with a fire extinguisher, although that
might be useful to put out whatever else it ignites). There are videos
on youtube.

So unless you have a good quality electronics bench supply with accurate
voltage setting (to 0.1V) and current limiting, it's not safe to do so.

I have done it with a mobile phone battery - doing it with something
bigger has bigger risks.

Since he needs under 500W to power the charger it might be easier to get
a mains inverter and run the existing charger from that (taking good
care with mains voltages in the field). There will be an efficiency hit
but probably only 10% or so. Assuming here that the charger is
sufficiently well designed to cope with a ropey inverter waveform. I
expect the charger will kill a nominal 300W toy inverter.

Otherwise you would need commission a charger from someone who is
competent to design it with the appropriate temperature, time, current
and voltage safety interlocks. Get it wrong and you brick the battery or
even worse start a lithium metal fire.

--
Regards,
Martin Brown