On Thu, 19 Aug 2010 13:08:28 -0500, bud--
wrote:
wrote:
On Thu, 19 Aug 2010 11:32:44 -0500, bud--
wrote:
wrote:
On Tue, 17 Aug 2010 21:42:58 -0400, "Stormin Mormon"
wrote:
Well, lets see. Now, lets look at the "irrelevant" factors, during a
series charge as you seem to prefer.
We start charging. About an hour later, the battery #4 in the line is
fully charged. We continue to pump in the two amp charge.
Hour two. Battery #3 is now fully charge. Battery #4 has been over
charged for the last hour, and is losing water as it electrolyzes to
hydrogen and oxygen.
Hour three. Battery #2 is fully charged. Battery #3 is rapidly losing
water. Battery #4 is nearly dry. Candidly, I think you are mistaken.
You forget, series charging of a string of batteries is NOT constant
current.
If you have a series string of batteries the current through each
battery is not the same - constant current? Please explain.
It is constant voltage - and the current looks after itself.
And I am NOT mistaken. I worked in the automotive field for many
years, and the batteries in the warehouse were allways recharged every
couple of months with the old Tungar battery charger - which was set
to the proper VOLTAGE for the series string, and after several days of
charging all the batteries were fully charged, and evenly charged. If
someone miscalculated and set the voltage too high, they were all hot
and gassing.
Charging a set of batteries in series, like a golf cart, you want all
the batteries to be the essentially the same - type, amp-hour capacity,
aging effects. And they should be used as a series string so their state
of charge (as they are used) is about the same for each battery. In an
old battery string you shouldn't replace one of the batteries.
Charging over several days is closer to a float charge.
If you charge at significant current you can get what Stormin nicely
describes. Why do you think what Stormin describes won't happen.
Generally we recharged at 2.3 volts per cell for a day or two, then
2.4 volts for another hour to 3 hours, depending on temperature etc.
Hydrometer testing of one or two batteries in the string told when the
batteries were fully charged - or simply checking to see that all the
cells in a battery were gently and evenly bubbling.
You probably have batteries that are close to fully charged when you
start and what you were doing was closer to a float charge.
If you have a few amps to very different batteries or very different
state of charge Stornin has a good description of what will happen.
The batteries varied from motorcycle and lawn tractor batteries to
deisel truck batteries - 6, 8, and 12 volt - AH ratings from 12 to
300+, and cca from about 50 to over 1000.
So are we going to talk about trickle charging a series string of
batteries over several days or charging over several hours, like is
virtually always done - like for golf-carts?
Evenly bubbling in a series string is an "equalization" charge and is
occasionally done in a series string like a UPS.
If you charge in parallel and one battery is partly shorted (Low
resistance) it hogs all the power and overheats, while the rest of the
batteries get virtually nothing - and if the charge is not high enough
for that scenario, the bad battery drains all the good ones.
Partly shorted is a red herring.
No it's not. A battery with a lowwer than normal resistance is partly
shorted unless it has a VERY LOW resistance, in which case it is
shorted. Deteriorated separators or large amounts of sediment in the
bottom of the case can cause a "partly shorted" cell - which usually,
eventually, becomes a shorted cell.
So what? There are equivalent problems in a series string.
You can charge normal batteries in parallel. You are OK if it is at a
float charge level (which is close to what you were doing). For a higher
voltage (producing a significant charge current) for a timed period, if
the state of charge is different or amp hour capacity is different you
may lose water in some of the batteries (same as leaving a battery on a
charger too long). It is a little safer than series in that batteries
that are more discharged will have a higher charge current. In a series
string the currents are all the same.
Which is the general idea. Low charging rate - constant voltage, not
constant current.
Which is not what you said you were doing in the warehouse. You said
that was series, not parallel. So what are we talking about? Or are you
still misunderstand that series is constant voltage, not constant current?
There aren't a lot of applications that heavily discharge battery sets
(golf-carts) and then trickle charge them.
What is the best battery setup for an electric vehicle (assuming you
MUST use lead acid batteries)?
A series string of 12 300 ah 6 volt batteries for 72 volts, or a set
of 12 300 ah 12 volt batteries set up Series/Parallell?
And what is virtually "required" in order to successfully use the 12
volt batteries?
To use the 12 volt batteries you need to have equal length, equal
resistance cables connecting the individual batteries in parrallel
pairs - and then also connecting the parrallel pairs in series so you
essentually have a ballanced grid tying all the batteries together -
(and the batteries pretty well have to be identical - down to being
dfrom the same production run and date code). that way a bad cell will
only kill 2 batteries - the defective one and the one directly
parallled with it.
In a series string, even in a high load situation like an EV, the
batteries should be of the same nominal capacity as far as AH and CCA
rating, but are not NEARLY as sensitive as in a parallel situation.
For a series string that is what I said (and what Stormin said).
Not so much for charging, but definitely for DISCHARGING under high
current conditions. My Fiat drew over 400 amps under accelleration -
making battery characteristics pretty important.
You disagreed with Stormin - that your warehouse charged very dissimilar
batteries in series. Your statement above disagrees with that and agrees
with Stormin.
You changed the subject by changing from a normal charge - over hours
(golf-cart) - to a trickle charge - over days. So which are we talking
about?
On the electric car it was charged with what was basically a heavy
golf cart charger - and in order to get anything more than 12 volts -
you definitely need a series string of batteries - and if they are in
series to provide the voltage required, you would not normally charge
them in parallel.
The one setup I used DID use series / parallel connections - with two
series strings in series with each other for higher speeds, and in
parallel with each other for high torque and low speeds. The two
strings were charged in parallel - and it was NOT a satisfactory setup
in the long run.
Much better to just use a high voltage series string and a good pulse
width modulated speed controller - which I did not have at that time.
Unlike you guys, I have built and driven electric vehicles. I've "done
it" - and belive me, series works a LOT better than parallel.
The thread was about series strings of batteries - golf carts - until
you brought up parallel charging. Nobody talked about a parallel set of
batteries for a power application. Changing the subject yet again.