Mixing LI Po ratings

[tedmales]

I was wondering if you could mix battery amp ratings. On my AX10 I have 2 850 11 volt li-po's and would like to get more run time. I currently get about 20 minutes with a mamba max and 7t motor. Could I run a (just guessing at numbers) 2000mah on the rear axle and a 1290 on the front to get a little more time, or would they just hurt each other. ( I do not have room on the front axle for anything bigger than the 1290mah) I am thinking no, but wanted to make sure. I found some max amp 1100 mah, or the 1290mah would fit where I need them to be, but really wanted in at least 3000mah to have a decent run time. Help a newbie out.
Thanks
Ted

[XPLORx4]

If you are intending to connect the two batteries in parallel, then I believe the answer is no, you cannot mix different mah lipo's together, since the lower mah batteries will become discharged before the higher mah batteries, and they will become damaged. You could pick up a pair of 1300mah batteries, which would give you a total of 2600mah. The battery linked should fit on the optional Axial battery/servo tray.

[Scottmisfits]

How much runtime do you want/need? I know I'm over an hour with a 1500mAh with an 85 turn. Even with my R2 and a 27t I'm getting close to 45 minutes.

[tedmales]

Originally Posted by Scottmisfits

How much runtime do you want/need? I know I'm over an hour with a 1500mAh with an 85 turn. Even with my R2 and a 27t I'm getting close to 45 minutes.

An hour would be great. But 20 minutes is not going to cut it. I could buy more batteries, but I am limited to what will fit where I have to put them. I think I might even look into a 5000mah pack and put it on top of the chassis top plate. I would like about 45 minutes of run time. I think this 7t puller motor needs alot of power.

[xirtic]

Originally Posted by tedmales

An hour would be great. But 20 minutes is not going to cut it. I could buy more batteries, but I am limited to what will fit where I have to put them. I think I might even look into a 5000mah pack and put it on top of the chassis top plate. I would like about 45 minutes of run time. I think this 7t puller motor needs alot of power.

1. Are you certain that you have everything setup correctly? Most of the guys that I crawl with are running between 1000mah and 1500mah....and we all average about an hour per pack. This includes guys running Mamba's as well as Novak setups. 20 minutes just sounds off.

2. If you put that 5000mah up on top, that will really mess with the CoG.

I am not judgin the choices....I am just curious about what is going on with the rig.

[Chris_The_Battery_Man]

Mixing lipos = dead lipos... No Bueno

[8onick]

Originally Posted by xirtic

1. Are you certain that you have everything setup correctly? Most of the guys that I crawl with are running between 1000mah and 1500mah....and we all average about an hour per pack. This includes guys running Mamba's as well as Novak setups. 20 minutes just sounds off.

2. If you put that 5000mah up on top, that will really mess with the CoG.

I am not judgin the choices....I am just curious about what is going on with the rig.

following along 'cause i wanna get more runtime myself. like tedmales above, i run the HH 7T cobalt puller motor. it likes to drain batteries quick. i get about 15 minutes with regular 8cell nimh. would like to hear from others running that motor that are using (which) lipos, what MAH, and are you running 2 lipo packs?

thanks

[Chris_The_Battery_Man]

You will just und up over discharging the lower capacity pack and killing after the first run or 2... So it's not a good idea to do that unless your rich and want ti buy lipos all the time

[tedmales]

Originally Posted by 8onick

following along 'cause i wanna get more runtime myself. like tedmales above, i run the HH 7T cobalt puller motor. it likes to drain batteries quick. i get about 15 minutes with regular 8cell nimh. would like to hear from others running that motor that are using (which) lipos, what MAH, and are you running 2 lipo packs?

thanks

I do tried to change the timing in my speed control, hopefully it will help. I am going to order a 45turn motor and I might not have the power, but I should get the run time. I read about other guys saying they get over a hour with the 7t and 2200 mah lipo, and I want to know what they are doing. My guess would be they are not getting them time they say.

[oberon crawler]

Originally Posted by tedmales

I was wondering if you could mix battery amp ratings. On my AX10 I have 2 850 11 volt li-po's and would like to get more run time. I currently get about 20 minutes with a mamba max and 7t motor. Could I run a (just guessing at numbers) 2000mah on the rear axle and a 1290 on the front to get a little more time, or would they just hurt each other. ( I do not have room on the front axle for anything bigger than the 1290mah) I am thinking no, but wanted to make sure. I found some max amp 1100 mah, or the 1290mah would fit where I need them to be, but really wanted in at least 3000mah to have a decent run time. Help a newbie out.
Thanks
Ted

Well I'm gonna go against the grain here and say that you can connect a 2000mAh and a 1290mAh 3s lipo toghther in parallel permanently and it will work safely and not damage cells or esc's.
you could even parallel up the balance taps and have it as one big battery and balance the whole thing from one connector.

I do not think that a big 3s lipo on the rear axle will be at all good for crawling and i also do not think that you should need anywhere near 3Ah 3s lipo for a damn Ax10!! lack of battery capacity is not your problem, too much power consumption is your problem.

There's got to be something wrong with timing or drag or something, if 7t pullers use that much power than they're not worth it in an ax10.

unless you're rock racing or something you could run a goat on a single 2s 1290 and get 30 min easy, on a 2000 you could get well over an hour.

I'd like to know what JRH thinks about your short runs with your puller!
He'd know best what they usually run at.

The reason i give for the ok on running parallel lipos of different capacity is that the packs will always be at the same voltage ie. the smaller pack wont end up going to a voltage below the larger pack.

[JohnRobHolmes]

Are you running the two 850 packs in parallel? One will not handle a 7t puller. I would want to see at least 40 amps continous on that motor.


You can run different capacity lipo in parallel as long as the voltage is the same. Not really an ideal setup, but the higher capacity pack will drain faster and they will both discharge to 3v/cell at the same time.

[Chris_The_Battery_Man]

Originally Posted by JohnRobHolmes

Are you running the two 850 packs in parallel? One will not handle a 7t puller. I would want to see at least 40 amps continous on that motor.


You can run different capacity lipo in parallel as long as the voltage is the same. Not really an ideal setup, but the higher capacity pack will drain faster and they will both discharge to 3v/cell at the same time.

Although there is a chance I am wrong, I am going to have to dis-agree... 2 packs of different capacities is not the best idea. The lower capacity pack will over discharge because it will only be able to go so far and the larger pack will pick up the slack. While the larger pack is still draining to 3v, the smaller pack will dip way below that. The cells will average out in voltage and not stop when the smaller one needs to.


There is a reason this is never done by any of the mayjor lipo companies or Nimh for that matter.... Every lipo company doing packs in parallel uses the same capacity and brand of cell. Not a good idea to mix capacities, brands, or different C ratings....

[oberon crawler]

I'm with JRH on the parallel packs.
As the packs are connected in parallel there is the opportunity for current to flow between the packs, this is how the smaller battery won't end up going being damaged, the large pack can sipmply chage the smaller pack during a run.
Also the parallel connection means that the same voltage must appear on the terminals of both packs (negating voltage drop caused by current flowing through the battery wires, this is very minimal however as the resistance of a couple of inches of 14g wire is very low)

A great analogy for understanding DC electricity is to think of water flow in pipes, where;
Flow = Current
Pressure = Voltage
capacity (mAh) = volume ie. Gal

So picture this, Two open top tanks of water, one is 1 foot high and 100gal (bath tub), the other is 1 foot high and 1gal (bucket) now if you connect the bottom of the bucket to the bottom of the bath and tee these pipes together the level (head pressure/Voltage) of the two will be the same. This is because the higher level in one container can flow into the lower container untill the pressure at the tee connection is equal. If you drain 50.5 gal from the tee the level will be 50% in both containers and 50gal came from the bath and .5 gal from the bucket. The bucket will never be empty while the bath has water in it.

If JRH says you need 40A then a combination of 20C batteries totalling 2000mAh battery should supply it.
Sorry for the long reply but i can't explain myself clearly in one line.

[tedmales]

I found some 1500 20c lipos and they will fit. That one is almost the same mah I have now, and I will have 2. I have my 850 in paralell. One of the things I found was my speed control was set to auto lipo and it would cut out at 10 volts. I switched it to 9. That might help. I thought I could mix batteries and get more time, but I think I will probably just go with 1 5000 on top. Hopefully it will not make my car to top heavy.

[JAM MaxAmps.com]

Parallel pack running: Packs must have the same capacity, C rating, age , number of cycles, and the same voltage. Capacity increases voltage stays the same.

Series pack running: Packs need to be the same capacity, C rating, age, number of cycles, BUT you can mix a 7.4 volt 2S pack with a 11.1 volt 3S pack to get a 18.5 volt 5S pack ( a 2S 5000 in series with a 3S 5000 to get a 5S 5000). Capacity stays the same voltage increases.

The reasons are that yes different capacity cells, different age cells, and different cycle amounts on a cell will all affect the discharge rate. Thus the reason you don't see any companies mixing a say 800 cell with a 1000 cell to get an 1800 2S pack.

And Johns right about that 7T cobalt motor. I wouldn't use any thing less than than a 3S 2100 with it. A really good pack would be our 25C 2200 3S or 4S. I know a few guys that are putting these accross the rear axle. http://www.maxamps.com/Lipo-2200-111-Flight-Pack.htm

Best regards,


Jason

[Chris_The_Battery_Man]

Lets not forget the mixture of different IR ratings either. Long story short... Unless you want to replace killed lipos, dont do it. The smaller pack WILL over discharge

[floogldood]

Any two packs can be paralleled as long as the voltage is same (number of cells)

They can be charged and used together without issue.

[Chris_The_Battery_Man]

Originally Posted by floogldood

Any two packs can be paralleled as long as the voltage is same (number of cells)

They can be charged and used together without issue.

Not true... Yes it will work and make your car move, but not work like it should. They will equalize eachother when not under load, but under load they will not equalize one another and end up killing to smaller cell and possibly put it into negative voltage. Lipo cutoffs generally cut off when the pack is under load because a battery un-loaded will not show that it is actually ready to stop. Yeah if they are paralleled, and your not driving the car, then they will ballance out eachother, but who turns on their car with the intention of not driving it...??


With how touchy these batteries are I wouldn't personally want to A: risk fire and B: if your trying to save money by utilizing 2 packs to get better run time... Then use them as seperate packs. That way your not risking ruining 2 packs or fire.


As I said and I believe JAM did too... There is a reason this isn't done in the first place. Lipos are not new to the hobby industry. If this worked, you would see it more ofted. Mixing brands, C ratings, and capacities is just not a good Idea with any battery.

[floogldood]

Both packs will share an appropriate amount of load and even during the discharge will stay at the same voltage.

There's no way that a parallel connection can force either pack to negative voltage. You are confusing this with series connection where a smaller pack would run out first and be pulled right past zero volts to negative voltage and ruined.

I'm sure even a grossly mismatched pair of packs would not cause any trouble if discharged towards the highest/largest rated pack. I will hook a large capacity pack with high discharge rating up to a tiny pack with low discharge rating. This should be the worst case scenario if discharged at the combined total discharge rate. (in otherwords pulling the larger pack at 20C and also pulling the tiny 8C pack at 20C) This is the only case where it can concievably give trouble.

Would anyone like to pick two very different packs? They just have to be same cell count.

[JAM MaxAmps.com]

Yeah don't listen to what Chris or I say. We only work with batteries for a living and don't know what we are talking about. Were only hear to give false information to you all.

Good luck with your experiment and if soemthing goes wrong don't come back and Blame either of us. As we have both clearly stated it's not a good idea and it's not recommended.

If anything your showing everyone how and why accidents can happen with Li-Po's.

Take care.

Jason