Parallel NiMH packs charging = good idea?

[Form]

Just got myself an electric and two identical battery packs for it. I was wondering if parallel charging is a good idea or not with NiMH packs. I got a parallel adapter for plugging both batteries in the truck so I would use this if parallel charging can be done.

Also, what settings should I use on my charger? (amperage, etc. compared to a single pack? What about the number of cells?

 

[frddyj]

hi mike,

please provide a link to your packs & a link to your charger.

 

[Form]

Here you go:

Charger: http://www.dynamiterc.com/Products/Default.aspx?ProdID=DYN4053
Packs: http://www.amainhobbies.com/product...ies-1-1200mAh-1-16-Scale-Battery-72-Volt-NiMH

 

[frddyj]

based on the charger rating for NiMH packs 1-8 cell and you have 2 x 6 cell packs i wouldnt do it.

1200 Mah packs shouldnt really take that long to charge one by one.
my son's 4500Mah pack takes about 30minutes at 1c.

if you want a faster charge, you COULD jack up your charge rate a bit, but i'd hit them with a temp gun now & then just to make sure.

eace:

 

[Form]

based on the charger rating for NiMH packs 1-8 cell and you have 2 x 6 cell packs i wouldnt do it.

1200 Mah packs shouldnt really take that long to charge one by one.
my son's 4500Mah pack takes about 30minutes at 1c.

if you want a faster charge, you COULD jack up your charge rate a bit, but i'd hit them with a temp gun now & then just to make sure.

eace:

30 minutes?? I charged my 1200 MAh packs at 1A (they recommend .3A for battery life and 1.2A max for performance) and it took 1h30… What's 1C?

 

[MikeK1981]

30 minutes seems a little fast for a 4500mah battery at 4.5 amps. My 3000mah batteries take like an hour at 3 amps. Maybe there is a difference in the internal resistance of our batteries?

 

[Bankrupter]

a C is 1 Amp per 1oo0 mah and yea 4500 @ 4.5 amps is normally one hour give or take whats left in it

 

[frddyj]

30 minutes seems a little fast for a 4500mah battery at 4.5 amps. My 3000mah batteries take like an hour at 3 amps. Maybe there is a difference in the internal resistance of our batteries?

VVV i think thats the answer to your post Mike. It in the kid's stampede and we don't run it till it wont run anymore, so even though it wont power the truck for a good run, (without recording the #'s) its safe to guess there's prob still a fair amount of juice in it.

give or take whats left in it

however, if i can remember rite it took a bit over a hour first charge. (don't quote me though, its been over a year so i can only guess).

 

[frddyj]

a C is 1 Amp per 1oo0 mah and yea 4500 @ 4.5 amps is normally one hour give or take whats left in it

yep, thats prob just about right if you drained the whole 4.5 A out of her. Not likely gonna take that long after the initial charge.

 

[Form]

So parallel charging would not be a good idea in my case because of the number of total cells in my packs (12) being too high for the number of cells supported by my charger (8) ONLY, or…?

I mean if my charger did support 12+ cells would it be OK or not, and why?

What about the two batteries being charged one after the other… say I charge one pack and come back later to plug the second one after say 3 hours then wait another 3 hours (when I happen to be able to change the batteries). Would the first pack discharge too much for the batteries to stay in "sync" or something for running in parallel / series?

Anyone got a good guide(s) for battery maintenance & charging with something like the charger I have?

Thanks for the clarifications guys! I'm not very informed when it comes to electric…

 

[Mickey]

batterys that are run in parallel don't increase in cell count just storage capacity, so if they are wired+ to + and - to - it is still a 7.2 volt battery you have that has 2400mah . if they are wired in series + to - then it increases to 14.4 volts with 1200mah. by this thinking you should be able to charge them in parallel but i would watch the temps on them just to make sure that one batt isnt taking more of a charge then the other

 

[Form]

batterys that are run in parallel don't increase in cell count just storage capacity, so if they are wired+ to + and - to - it is still a 7.2 volt battery you have that has 2400mah . if they are wired in series + to - then it increases to 14.4 volts with 1200mah. by this thinking you should be able to charge them in parallel but i would watch the temps on them just to make sure that one batt isnt taking more of a charge then the other

What about the charger's cell count & peak detection? Do you think it would still detect 6 cells and stop charging at the right moment with two batteries?

 

[Bankrupter]

it will see it as 1 battery not 2. Lipos sync charge caz they have balance wires to each individual cell and the chargers know whats going on. only the bigger better chargers do it too

 

[frddyj]

it will see it as 1 battery not 2. Lipos sync charge caz they have balance wires to each individual cell and the chargers know whats going on. only the bigger better chargers do it too

Yep. there is no real benefit to charging your NiMH packs in parallel on the same charger (if you can even do it), here is why.

For sake of argument say you charge 1 x 5000 Mah NiMH pack & your charger is capable of charging at 5A (1c in this case) Max & it takes you an hour to charge.

If you connect 2 x 5000Mah packs (now your up to 10,000Mah or 10A) and still charging with a charger max 5A so you are now cutting your charge current in 1/2 to 2.5A per pack or .5c rating.

So in that case there is no benefit to do this; just charge one pack & then the other. Not sure your ultimate goal is to charge your packs faster or not.

Like B/R points out, you can purchase a sweet hyperion 615i DUO III (which is essentially 2 separate chargers/balancers built into 1 box capable of charging 2 separate NiMH packs at the same time at up to 15A (or 3c with the 5000Mah packs used in our example) but the charger is gonna see your 6-cell NiMH pack as a single cell because the pack is not wired with a balance plug as balancing is not necessary for NiMH packs. But, you would have the option of charging 2 x 5000Mah packs at the same time at up to 15A supplied to each pack so it would only take you an hour. Problem is its gonna cost you upward of $400 by the time you buy the charger and a suitable power supply & not worth it if your only gonna be charging NiMH & Nicd.

Does this answer part of your question Mike? If yes, then we can move along to the discharge question you asked, but this post is already getting way too long to read so we'll address that separate if ok with you my man.

 

[Form]

Yep that was pretty informative frddyj, thanks!

My goal actually is to plug both my batteries in the charger in the morning (there's still someone at home, so no fire hazard in case something goes wrong) and have them charged when I come back from work without requiring someone to watch the time and switch packs. Since the charger has peak detection there should be no problem letting the packs plugged in after they've finished charging right?

So based on what you say, I could plug my two packs in parallel and they would be charged as one single cell 2400 MAh pack. Each pack would charge at 0.5A if I keep my charger at 1A, taking double the time it takes for charging a single pack.

Then I could crank the amperage up to 2A to get 1A per pack and have both charge in about the same time it takes for one pack at 1A?

All that with no adverse effect on the life of my packs. Is that correct?

Thanks for bearing with me!

 

[MikeK1981]

Just teach the wife or whoever is there to charge your packs for you. Then you got no worries and no hassle lol. I'd just charge them at work if it were me. I usually charge mine at the end of the day while I'm just hanging around the house before I go to bed that way they are good to go for next time.

 

[frddyj]

So based on what you say, I could plug my two packs in parallel and they would be charged as one single cell 2400 MAh pack. Each pack would charge at 0.5A if I keep my charger at 1A, taking double the time it takes for charging a single pack.

I was actually trying to point you in the direction of charging the packs one at a time with that charger because that is how the mfr intended it to be used (charger) and I'm not sure that it would work if you split the charge lead to 2 packs.

that example was more of a "if it could be done" then this is how the numbers would break down in terms of charge time & current flow.

not saying it 'wont' work, ive just never done it or heard of it being done. if you go for it, i wouldn't leave it alone.

your best bet would be to call the manufacturer of the charger and ask them directly.

Then I could crank the amperage up to 2A to get 1A per pack and have both charge in about the same time it takes for one pack at 1A?

idk man, sounds like it could be a bit risky. again, call the manufacturer with this question.

it could put a strain/put too much load on the charger & when you increase current flow, heat is gonna be a natural by-product.

All that with no adverse effect on the life of my packs. Is that correct?

idk about that.


...

if you do end up calling the charger manufacturer & trying this out, can you please make a thread detailing what you did and how it worked (and your convo with the mfr?)

you got me interested now to see if this is gonna work. plus rep for you thinking about a different way to skin a cat Mike.

 

[frddyj]

Just teach the wife or whoever is there to charge your packs for you. Then you got no worries and no hassle lol. I'd just charge them at work if it were me. I usually charge mine at the end of the day while I'm just hanging around the house before I go to bed that way they are good to go for next time.

I'm with Mike on this

i don't charge any batt while its in my truck, nor would i leave a batt of any type alone while charging. Ever!

 

[Form]

if you do end up calling the charger manufacturer & trying this out, can you please make a thread detailing what you did and how it worked (and your convo with the mfr?)

I'll send them an e-mail with a link to this thread and I'll report back on what I learnt and what their official answer is. Stay tuned!

If anyone got something to add feel free to do so!

 

[Form]

Ok here's the update:

Me:

I'm wondering if it's possible to charge two NiMH 6-cell 1200 mAh battery packs (the stock Mini E-Revo ones) IN PARALLEL on my Dynamite Vision Peak Ultra. I'm guessing that it would be possible to charge the two packs at once using the Traxxas parallel adapter. The packs would then be seen as a single 2400 mAh pack by the charger. If I was charging one pack at 1A, then plugging two packs in parallel would give 0.5A per pack, taking double the time to charge. I could then crank up the amperage to 2A to get 1A per pack and get my two packs charged in parallel in the same amount of time as a single pack.

Is this correct or is there something I did overlooked / did not understand?

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Them:

Thank you for contacting Horizon Hobby Product Support. We do not recommend the use of a parallel adaptor to charge both batteries at the same time. If one battery is not at the same capacity when the charge process starts it may not give the lower of the 2 batteries a proper charge. If you should need further assistance regarding this issue please reply to this e-mail for further assistance.

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Me:

Is the different charge level of the two packs the only issue?

I always use my packs at the same time in the same kit so they should *
always have approximately the same charge level.

If the batteries are equally discharged this way, would it be ok then? *
Is there a risk in doing this?

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Them:

Thanks again - The two packs may not be at the exact same state of charge, and their specific voltages might be off. *This could easily cause damage to one or both packs - therefore we cannot recommend this method of charging. *Separate charge cycles for each pack will ensure long life for both packs and your chargers. *If you should need further assistance regarding this issue please reply to this e-mail for additional support.

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Honestly I can't say this helped much… any comments?

 

[frddyj]

Honestly I can't say this helped much… any comments?

I think it helped a ton. This is a great thread Mike, you asked your question and got a great answer from someone who knows what their talking about. Got a very clear, detailed explanation based on facts and not "i think you should do this."

If this question comes up again, i will link to your thread here for explanation.

i don't charge any batt while its in my truck, nor would i leave a batt of any type alone while charging. Ever!

Forgot to mention the reason why:

​

 

[Form]

I think it helped a ton. This is a great thread Mike, you asked your question and got a great answer from someone who knows what their talking about. Got a very clear, detailed explanation based on facts and not "i think you should do this."

I agree their answer was clear, but I would have liked a bit more info about WHY it would damage the packs to do this… how does the charger react? Does it overcharge the maxed out pack until the non-full one is fully charged? Does it undercharge the non-full one, stopping at the point where the full one is done charging? Does it keep charging indefinitely because it can't pinpoint the number of cells or something? Etc.

Anyway it seems like it's not a good idea to charge in parallel. Too bad.