can NiCd be charged in parallel ?

N

needWheels

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I figured I better ask this question instead of assuming it can be done.

What happens if you try to use a "smart charger" (using negative delta v) on a string of nicd's in parallel?

Will a 12V 1A charger be able to charge 10 cells x 3 ?

By the way, are dumb chargers simply a transformer outputting 15V 1A to a 12V series of batteries?
If it's watched/timed, is that "safe" ?
 
Really? Ugh.

What's a good approach then to charge a massively parallel battery pack?

Do I have to separate each group and simply charge in series?
 
charging nimh or nicd in parallel is the best way to destroy your packs and charger.

always charge in series or on seperatly isolated chargers.

tell me more about your cells and ill tell you the best way to charge them.
 
I just read up on why it's a horrible idea. I think I get it now.
Apparently at the end of it's charge cycle, nicd (and nimh) drops a bit in voltage
which causes the parallel'ed pack to "spill over" into it. Very bad.

Well heck. Back to the drawing board.
I wanted a simple solution to plug it in and stop fiddling with wires like on my SLA.

I think I will just hold off until next year and hope that LiFePo4 comes down in price.
 
i think you can use diodes at the end of each series string to prevent one string from being able to discharge into another, you can use a low voltage high amperage shottky diode since the reverse bias voltage would only be the difference between the lowest voltage string to the highest voltage string, which i would think is pretty small. there would be a little power loss but not much, i saw some that had a .3V drop at 50A, 15W of loss.

actually nevermind i don't think it will work, i must have been thinking about something else, the way i had pictured it would prevent the charger from being able to charge the pack!
 
I appreciate the attempt dirty_d.

I think the solution in the end is to go with only two strings of serial cells and then parallel them.

Then I will use two 40 cell chargers so it can be done in one pass.

The problem is 40 cell chargers are like $50 shipped so this project will have to wait.
 
oh no, sorry i think i was right, i just had it backwards you would have the diodes arranged to allow the charger to pass current through the pack, that way they cant discharge at all into one another, but they would have to be removed once the pack is charged. im thinking the charger would have them built in and it would plug into one of those connectors with a bunch of connections on the pack.
 
dirty_d said:
oh no, sorry i think i was right, i just had it backwards you would have the diodes arranged to allow the charger to pass current through the pack, that way they cant discharge at all into one another, but they would have to be removed once the pack is charged. im thinking the charger would have them built in and it would plug into one of those connectors with a bunch of connections on the pack.
Click to expand...

This is an improvement, but it doesn't stop a full battery from steeling all the charging current from the lagging battery. So one of the batteries gets cooked, just a bit slower this time.

Marty
 
I tried it with an ammeter once just to see what would happen (nimh). The voltage stayed constant until one pack became charged, it then hogged most, but not all of the current, so there's was no problem with packs discharging into each other. The problem is that the charger won't terminate and thus will destroy one of the packs whilst not correctly charging the other. I'm sure its possible to do with a clever bms. you can charge 90% on Voltage termination alone just the last part thats tricky
 
Hey needwheels! where can u get 40 cell nicad chargers for 50 bucks?
otherDoc
 
you could charge multiple Nimh batteries from one charger if they were seperatly charge terminated based on heat. technically they would be in parallel untill one gets hot when it would stop the charge for that battery.

you would need to buy a thermostat circuits for each paralleled string.
 
I hate to admit this but way back a few years I charged 2 30 cell 5 amp Nicad packs in parallel!!!! :oops: I used my trusty Astroflight 112D and did it about 15 times over 3 weeks! They were fine! I would charge the single packs at c/10 each week! I believe the Astro has a very sensitive deltaV cutoff, but no temp sensing! Then I read I shouldnt do it and stopped!!!
otherDoc
 
docnjoj said:
Hey needwheels! where can u get 40 cell nicad chargers for 50 bucks?
otherDoc
Click to expand...

sorry I missed your question from the other day
all-battery (tenergy) has a 40 cell charger (doesn't have a heat sensor though, just delta v)
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=330171693236
(remember to use the cashback from live.com if you buy from ebay)
does 30-40 cell (36v-48v) @ 1A (which probably takes forever)

They make a 2A version for like $90 but it's not on ebay, just all-battery.com
 
Thanks needwheels!
otherDoc
 
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