Multiple lead-acid charging



No temperature compensation?
...Jim Thompson
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| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
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Jim Thompson wrote: <snip description of 3 stage battery charging>

"Education is a process of decreasing deception" :)
I've tried to persuade the OP to post details of what battery bank he is intending to use, so that folks here can suggest suitable chargers. He was still at the "constant voltage" state of learning and so I posted the simplest description of 3 stage charging that I could find relating to a real charger..
But, of course, you are very right. But I was leaving the effect of temperature on the selection of charging voltage until later... ;)
-- Sue
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OK ;-)
...Jim Thompson
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Well, I haven't determined my load requirements exactly yet, as I am still in the design phase. But let's assume I have this case:
10 deep-cycle batteries in parallel. 100 A-h each, 700 cca. 12 Vdc 2.5 kW non-inductive load applied for one to three hours at a time. Charge in 48 hours or less.
Is this possible?
Don Kansas City
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if the batteries are rated at 100ahr @ 5hr rate 00ahr you require just over 200amps at 12vdc for 2-3hrs....keep the cabling between batteries large ...larger the better......so far so good get a high reactance steep taper charger 2:1 ratio 12vdc @ 125amps recharge time approx 1000*1.5/125hr recharge or less as your not taking the full capacity......equalise regularly and you should be up and away....would be easier to get 6 * 1000ahr cell strung in series to do the job tho....but either way should work fine
pat
wrote:

Well, I haven't determined my load requirements exactly yet, as I am still in the design phase. But let's assume I have this case:
10 deep-cycle batteries in parallel. 100 A-h each, 700 cca. 12 Vdc 2.5 kW non-inductive load applied for one to three hours at a time. Charge in 48 hours or less.
Is this possible?
Don Kansas City
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eromlignod wrote:

Yep, that can be done. However, is it possible for you to use 24Vdc, instead of 12? That would greatly reduce the cost..
-- Sue
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On Thu, 19 Jun 2008 15:11:19 -0700 (PDT), eromlignod

2500 watts is about 210 amps at 12 volts, or 630 Ampere-hours if run for 3 hours.
Since your batteries are capable or 1000 AH to full discharge, this is possible, but a bit harder on the batteries than most would like - it is widely recommended that you don't discharge more than 50%, so your battery life will likely be somewhat less than it would be for a more conservative use.
So, you have to restore 630 AH, plus ~20% for battery inefficiency, say 750 AH in 48 hours, so you might get away with a 15 Amp charger, but a larger charger will give some safety margin.
It is suggested that a flooded lead-acid battery should not be charged at more than .25C (where C is the ampere-hour capacity of the battery.) For your battery bank, this means that you shouldn't use a charger capable of more than 200 - 250 Amp. Given your suggested use, a 250 Amp charger would recharge your battery bank in about 3 hours, but there is no need to use that big a charger unless you really need to recharge in that time. (and a slower charge will be easier on the batteries.)
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
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Peter Bennett wrote:

The problem is that most chargers today are "intelligent" - with a microprocessor onboard. They are designed for a range of AH and, if used with a greater AH - will interpret the greater time taken to bulk charge needed as a fault.
Changing to a higher voltage battery array reduces the AH needed. It also reduces the potential fault current, the cost of the infrastructure (cabling, protection devices, etc) and the cost of the charger. Plus will be more efficient.
However, if that isn't possible, I've found charger manufacturers to be extremely helpful. Including providing firmware patches to allow for out of spec AH battery arrays.
-- Sue
-- Sue
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<much snippage>

Where do you get that 0.6 amps? - the charger will never get anywhere at that rate.
According to the Xantrex Trucharge 20/40 charger manual, in the "Bulk" mode, the charger will deliver its rated current (20 or 40 amps for these chargers) until the batteries reach 14.4 volts. The bulk mode should get the battery to about 75% of full charge. At this point, the charger will switch to "Absorption mode", where the voltage is held constant near the gassing voltage, and the charging current will reduce as the battery approaches full charge. Eventually the charger enters "Float Charge mode", and reduces the voltage to 13.5 volts. (all voltages are for a nominal 12 volt system)
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
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Peter Bennett wrote:

as in:
"Note that this is from the description of a charger intended for relatively small batteries. The 0.6A in stage 1 would take a very, very long time to charge a big battery. For many intelligent chargers, this very, very long time would be flagged as a fault condition - hence it is important to get a charger rated for the AH of the batteries that are being charged."
Which you snipped from the very same post.

Where did you get a 20/40 amp charger? - many of these will never charge the OP's battery array as his total AH is > than this size charger's specification. The charger will sense that the bulk phase is taking too long, will flag a fault and stop charging. It may easily not be able to supply the current needed when equalisation mode is initiated..
The important thing is that the charger is matched to the OP's battery array - which will determine whether a 0.6A, a 20 A or whatever, charger is needed.
-- Sue
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This is getting far too complicated ......find yourself a forklift company with an old single or 2 stage charger for sale 12volts @ 125amp with a simple gas timer. because of the paralell strings this will prove much better than the modern chargers with fault detection and back up timers and will be a fraction of the price it will also accomodate equalising which you will need because no matter how fancy the charger it will only see the best voltage not the batteries that are lagging.
pat
wrote:

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