Mixed milli-amp NiMh batteries

[JLP75766]

I have 4 NiMh batteries and none of them match in Milli-amps.
I have a 1100,1200,1400,1600.
The manual says not to mix them I want to run in parallel for longer run times. Are these 4 batteries so far apart that I will do damage to something?
Could I use the 1400/1600 together?
Could I use the 1100/1200 together
What about the 1100/1600 together?
Thanks for your help.

[Traxxas Freak]

i was also wondering this

[minirevo]

what about running them in series for more power?

[Hughes500Bob]

"A complete discharge of a cell until it goes into polarity reversal can cause permanent damage to the cell. This situation can occur in the common arrangement of 6 cells in series, where one will be completely discharged before the others due to small differences in CAPACITY among the cells. When this happens, the "good" cells will start to "drive" the discharged cell in reverse, which can cause permanent damage to that cell.
Irreversible damage from polarity reversal is a particular danger in systems, even when a low voltage threshold cutout is employed, where cells in the battery are of different temperatures. This is because the capacity of NiMH cells significantly declines as the cells are cooled. This results in a lower voltage under load of the colder cells."

Basically .... Do not do it unless you are considering your packs expendable.

This is why you buy MATCHED PACKS once you go into race mode!

[JLP75766]

what about running them in series for more power?

I could run them in series but what I am looking for is more run time. The track I run on is pretty tight and more power is not needed. This thing has plenty of power for me as it is.

[JLP75766]

"A complete discharge of a cell until it goes into polarity reversal can cause permanent damage to the cell. This situation can occur in the common arrangement of 6 cells in series, where one will be completely discharged before the others due to small differences in CAPACITY among the cells. When this happens, the "good" cells will start to "drive" the discharged cell in reverse, which can cause permanent damage to that cell.
Irreversible damage from polarity reversal is a particular danger in systems, even when a low voltage threshold cutout is employed, where cells in the battery are of different temperatures. This is because the capacity of NiMH cells significantly declines as the cells are cooled. This results in a lower voltage under load of the colder cells."

Basically .... Do not do it unless you are considering your packs expendable.

This is why you buy MATCHED PACKS once you go into race mode!

I understand completely about matched cells are all about. What I am trying to do is use some odd batteries I have around for just bashing on a track in my yard and then getting a matched set for my formal racin at my local track.
I notice your quote said "for six cells in series" Does this same thing hold true for parallel?

[Adonnay]

Nope, no option. I'd never recommend this.

[kulangflow]

Does this same thing hold true for parallel?

If you are running an 1100mAh pack in parallel with a 1200mAh pack, when the 1100mAh pack runs out of capacity, the 1200mAh pack will have to handle the full load by itself, and you'll overdraw the 1100mAh pack which can cause damage to it.

If you know for certain that you consistently get 30 minute runtimes with those two packs in parallel, then just stop them at 25 minutes to avoid overdrawing either pack. Honestly it's not a good idea, but if you're not worried about those NiMH packs then it's worth the risk, IMO.

I would never ever do this with lipos though.

Like Hughes said, "Do not do it unless you are considering your packs expendable."

[JLP75766]

So....is it OK to run mixed Milli-amp NiMH batteries in series?

[Hughes500Bob]

Why do you want to add the weight of two batteries in parallel for longer run times when you can just stop and swap out batteries?

MiMH batteries are "the hardest batteries to charge". It's great to have a set or two for wet and bashing. They are safer for kids with a slow charger.

Lipos are about the same cost, faster to charge, easier to store, hold their charge longer, lighter in weight, etc. YES They require careful handling, but are not the hand grenades that some make them out to be. Balance tap Low Voltage Alarm plugins (about $5 each) are great insurance (always connect the - Gnd pin and float the 3S + end pin when using on 2S ..... leds should be lit). You can series packs of different voltages as long as the cell mAh capacity is the same. 2S + 3S = 5S If you run two lipo packs in series or parallel .... you can charge them both together safely using a balancer while charging (and correct balance tap adapters wiring!!). The balance tap and a good balancer gives you a lot of flexibility while charging lipos as each cell can be seen individually which is not the case with NiMH batteries. This is why a balance tap charger is so easy to use on smaller capacity lipos.

If you want to store your lipos "long term" just charge to 3.8 to 3.85 volts per cell and put them away. Every 6 months check and adjust. Keeping them fully charged for 4 to 6 weeks has never been a problem for me. Do not let them sit around fully discharged (3.0v to 3.3v depending) after running as they may get too low and damaged if you do not get to them in time to recharge.

OK .... This old electronic engineer is done typing for now. PLEASE consider the switch to Lipos. Buy the best charger / balancer combo you can afford. There are a lot to choose from so do your research. Do not overspend for a unit that can do 10S if you are never going to do more than 6S. Get a charger that can run on 12 volts DC or AC/DC. An AC only charger is useless at the field unless you have an inverter. Dual 12 volt 20 amp total supply on EBay for under $60.

[filmmaker]

I have 4 NiMh batteries and none of them match in Milli-amps.
I have a 1100,1200,1400,1600.
The manual says not to mix them I want to run in parallel for longer run times. Are these 4 batteries so far apart that I will do damage to something?
Could I use the 1400/1600 together?
Could I use the 1100/1200 together
What about the 1100/1600 together?
Thanks for your help.

Very good chance to damage the lower mah battery when you run them in parallel or series if you run the batteries down..

[MuddyTire]

Yes, you can safely run different MAH packs together in parallel as long as they are the same cell count. The voltages will balance out during consumption and they will drain evenly but at different individual amperage rates.

[Shelby VNT]

Never run batteries with different capacities together, in parallel, or series. It doesn't matter the configuration. If the capacity of the battery packs is different, one pack will run dump before the other, and if you continue to run the model like this, you stand a good chance of cell reversal, and damaging the lower capacity pack.

Think of it this way. If you have dual fuel tanks on a vehicle, and one is smaller, when the smaller one runs out of fuel, the other tank will still be powering your vehicle, but the suction for fuel will still be present on the empty tank. What do you think will happen?

[MuddyTire]

Lots of miss information in here. It is fine to run different MAH packs as long as they are of same number of cells i.e. nominal voltage. See topic.

[kulangflow]

I wouldn't call it "mis-information" if it comes from Traxxas, MaxAmps, and a few other battery manufacturers.

I can see the theory behind the information in that thread you linked, but I'd really like to see someone prove it in real life before advising people to risk their battery investment contrary to the warnings of the manufacturers.

[egnix]

Lots of miss information in here.

You can say that again!

[Hughes500Bob]

In theory parallel lipos of different quantities / same voltage in a slow current drain will self balance. But in a fast drain high current application the balancing may not keep up with the drain. For ME the electrical engineer with 32 years of high end computer circuits .... I say stick with matched packs for lipos (or darn close) and perfectly matched NiMH packs!! We have been precisely matching cells and packs in racing NiMH batts for years!!! Lipos are way easier.

[filmmaker]

Never run batteries with different capacities together, in parallel, or series. It doesn't matter the configuration. If the capacity of the battery packs is different, one pack will run dump before the other, and if you continue to run the model like this, you stand a good chance of cell reversal, and damaging the lower capacity pack.

Think of it this way. If you have dual fuel tanks on a vehicle, and one is smaller, when the smaller one runs out of fuel, the other tank will still be powering your vehicle, but the suction for fuel will still be present on the empty tank. What do you think will happen?

I agree..
If someone tries this they will suck the lower mah batteries way below their safe pointe of no return, and poof.. out comes the magic smoke!

the smaller battery will lose!

[MuddyTire]

I agree..
If someone tries this they will suck the lower mah batteries way below their safe pointe of no return, and poof.. out comes the magic smoke!

the smaller battery will lose!

This is totally incorrect. Please refrain from electrical discussions if you do not know how electrical physics work.

[kulangflow]

This is totally incorrect. Please refrain from electrical discussions if you do not know how electrical physics work.

Muddy: Traxxas, MaxAmps, and several other battery manufacturers sure do have a lot to learn from you.

Again, I understand your theory, but we'd really like to see it in practice with this specific application before you go advising people to risk their investment based solely on the words/theory of someone who apparently knows more than the manufacturers.

To the OP: If you think Muddy knows more than the people who made the truck and the batteries, then go for it! If you're having doubts about that, then don't.

I'm not saying Muddy isn't right or can't be right. I'm not saying the manufacturer is always right. I just want proof, not theory, when the other side of the argument is coming from the manufacturers, who have probably also done a bit of homework on the subject.

[MuddyTire]

Muddy: Traxxas, MaxAmps, and several other battery manufacturers sure do have a lot to learn from you.

Again, I understand your theory, but we'd really like to see it in practice with this specific application before you go advising people to risk their investment based solely on the words/theory of someone who apparently knows more than the manufacturers.

To the OP: If you think Muddy knows more than the people who made the truck and the batteries, then go for it! If you're having doubts about that, then don't.

I'm not saying Muddy isn't right or can't be right. I'm not saying the manufacturer is always right. I just want proof, not theory, when the other side of the argument is coming from the manufacturers, who have probably also done a bit of homework on the subject.

Physics don't lie. They will drain evenly. It's impossible NOT to.

Please show me proof where the manufacturer shows in practice where it is harmful/dangerous/bad to run 2 same cell different MAH packs in parallel.

Soon as I get it setup I will absolutely be running all sorts of bat packs in parallel with my Revo. I would of in my RC planes long time ago but they are too weight sensitive and can't support 2 pack weights well.

RV motor homes and electric fork lifts have been doing different battery capacities for years. The batteries will work together drain properly and without issue.

[Jason_garrison]

I am an engineer for whatever that is worth and took several electronics classes and muddy is right,

If two 7.2V 1600mah packs equate to a single 7.2V 3200mah pack.

There is no reason why a 7.2V 1600 pack and a 7.2V 1400 pack would equate to a single 7.2V 3000mah pack.

Now the thing about that is if you drain the smaller pack too low you could ruin it or even worse if you are doing this with lipo, you could blow one up.

That is why manufacturers tell you not to do it, they dont want you to ruin packs. Most people are not careful about stuff like that and then will come on a internet forum and bash a company for selling a faulty product when it was user error.

[kulangflow]

From Kokam: "All battery packs connected together in parallel must have the same voltage and capacity
(mAh)"

From the E-Revo VXL owner's manual: "This is easily done with
a parallel Y-harness (Part #3064, sold separately). Be sure to only use the
Y-harness with identical battery packs; do not mix batteries of different
chemistries or capacities."

Here is a quick chat with MaxAmps:

Jason Melville : Welcome to MaxAmps.com live help. How can I help you?
Brian : Is it okay to run different mAh packs together in parallel?
Jason Melville : Nope packs should be same capacity to ensure equal discharge.
Brian : So if I ran a 1400mAh in parallel with a 1600mAh, would the 1400 get damaged?
Jason Melville : yes you risk damaging the pack.
Brian : I suspected as much, but wanted to make sure. Thanks for your help.
Jason Melville : your welcome.

Jason, you're actually making my point. Obviously they will work together, but the reason you shouldn't do it is because you can over-discharge the weaker of the two packs. Like I said before, you can do it if you stop running the truck before the weaker pack has been fully discharged.

[filmmaker]

This is totally incorrect. Please refrain from electrical discussions if you do not know how electrical physics work.

I completely disagree...

[filmmaker]

Muddy: Traxxas, MaxAmps, and several other battery manufacturers sure do have a lot to learn from you.

Again, I understand your theory, but we'd really like to see it in practice with this specific application before you go advising people to risk their investment based solely on the words/theory of someone who apparently knows more than the manufacturers.

To the OP: If you think Muddy knows more than the people who made the truck and the batteries, then go for it! If you're having doubts about that, then don't.

I'm not saying Muddy isn't right or can't be right. I'm not saying the manufacturer is always right. I just want proof, not theory, when the other side of the argument is coming from the manufacturers, who have probably also done a bit of homework on the subject.

I'm with you on this one.. things can look good on paper but in the real world things can be greatly different..
It's ok to run different mah together for short runs, but the lower pack will go down before the other pack and one may not notice it and ruin the pack..
we all want to see these minis run for a long time and not see them go up in the magic smoke..

[Jason_garrison]

From Kokam: "All battery packs connected together in parallel must have the same voltage and capacity
(mAh)"

From the E-Revo VXL owner's manual: "This is easily done with
a parallel Y-harness (Part #3064, sold separately). Be sure to only use the
Y-harness with identical battery packs; do not mix batteries of different
chemistries or capacities."

Here is a quick chat with MaxAmps:

Jason Melville : Welcome to MaxAmps.com live help. How can I help you?
Brian : Is it okay to run different mAh packs together in parallel?
Jason Melville : Nope packs should be same capacity to ensure equal discharge.
Brian : So if I ran a 1400mAh in parallel with a 1600mAh, would the 1400 get damaged?
Jason Melville : yes you risk damaging the pack.
Brian : I suspected as much, but wanted to make sure. Thanks for your help.
Jason Melville : your welcome.

Jason, you're actually making my point. Obviously they will work together, but the reason you shouldn't do it is because you can over-discharge the weaker of the two packs. Like I said before, you can do it if you stop running the truck before the weaker pack has been fully discharged.

I did not read anywhere in this thread that anyone said if you discharge them too low you wont ruin the lower end pack.

But as muddy and I have said, you can do it and it will cause no issues if you are careful. The companies tell you not to because they do not want to have someone say that they said it was ok to do and then ruin a pack.

From a pure electrical standpoint there is no issue with this at all if you remember the lower rated pack will drain first so just use your head and you will be fine. Its no different than running lipo packs on a car that does not have a low voltage cutoff.

[filmmaker]

I did not read anywhere in this thread that anyone said if you discharge them too low you can ruin the lower end pack.

But as muddy and I have said, you can do it and it will cause no issues if you are careful. The companies tell you not to because they do not want to have someone say that they said it was ok to do and then ruin a pack.

From a pure electrical standpoint there is no issue with this at all if you remember the lower rated pack will drain first so just use your head and you will be fine. Its no different than running lipo packs on a car that does not have a low voltage cutoff.

big difference is one may not notice the lower mah pack going dead and completely jack that battery..

[Jason_garrison]

big difference is one may not notice the lower mah pack going dead and completely jack that battery..

I dont know about you, but I every so often check the temps of my motor, esc, and batteries. If it gets hot, stop running. Pretty simple imo.

[kulangflow]

I did not read anywhere in this thread that anyone said if you discharge them too low you wont ruin the lower end pack.

But as muddy and I have said, you can do it and it will cause no issues if you are careful. The companies tell you not to because they do not want to have someone say that they said it was ok to do and then ruin a pack.

From a pure electrical standpoint there is no issue with this at all if you remember the lower rated pack will drain first so just use your head and you will be fine. Its no different than running lipo packs on a car that does not have a low voltage cutoff.

I think you and I are on the exact same page, Jason.

Muddy keeps saying that there will be no issues. "you can safely run", "It is fine to run", "The batteries will work together drain properly and without issue." He has not said that you need to be careful to not over-discharge the weaker pack, as you and I have been saying. It appears he is implying that the packs will drain equally so you don't need to worry about the weaker pack. This might even be true, but I'd like to see the proof first.

Of course there will be no issues if you are careful. The important part I've been trying to stress is the "being careful".

Muddy is effectively saying, "Do it, and don't worry about it."
You and I are saying, "Do it, but be careful not to over-discharge the weaker pack".

For the record, I think what Muddy is saying is absolutely correct in lower current applications or with high current batteries in high current applications. I want to see it work with high current applications with low current batteries. If that makes any sense. :-)

[Shelby VNT]

/\ I agree. If you have two packs in parallel, you have no idea when one dumps. You might notice a little loss of punch, but really, the model will still run.

Now the question is, why bother running two packs in parallel anyway? Yeah, it increases run time, and in the case of these trucks, it balances the chassis better, but really, you would be just as far ahead, and probably safer, to run the two packs separately, and get the same run time altogether. I'm not afraid to switch out battery packs. Is anyone?

The only reason I could see to truely justify running two packs in parallel is because the current draw of your motor and ESC is greater then one pack can handle on it's own. When you double up battery packs in parallel, you split the load. Instead of one pack supplying 60 amps, now each pack will supply 30 amps a piece. If one pack is not rated for 60 amps, two 30 amp packs will handle the job just fine, but here again, they should really be matched.

[kulangflow]

I will be running my packs in parallel to split the current draw and to save from having to switch out the packs as often.