hemiblas

Ok, I have a 14.8V 4S lipo battery at 4400mah and 12C rating. I was thinking of putting a 14.8V, 4S lipo battery 20C 2200mah in parallel on my brushless conversion to help out. I'm thinking at WOT the voltage dipps and this will help to keep it higher so I get more top speed and the batteries will stay cooler. There is no room for another 4400mah battery and thats why I was thinking of this.

What do you think will happen with an approx. load of 45A continous.
.
1. Both batteries will share the current load equally???? at 22.2amps each
2. The larger battery will put out more current???? and the smaller battery will supply less current???????
3. I will fry the smaller battery???????
4. Any other ideas.
5. This is a bad idea, just dont do it.

guver

My Feedback: (325)

I think with proper size P connections it will work fine. I am assuming you run the 4400 by itself right now on the vehicle?

If so the 2200 added to it will make things better (OTHER than weight/added connections)

1,2 The batts will automatically share the correct % of load.

5 good idea.

dirt101

I say throw them all on there in parallel. then run it and chec each batteries temperture to get an idea whats being stressed the most and if it is being overstressed get a 5000mah 4s off of maxamps. or send true rc an email and see what they can do for you. they build custom packs at no charge just pay for the cells and they will build them.

Straick7

If my understanding of how the batts work is correct, it is a really bad idea to run two lipo packs of different capacities in parrallel with each other. From what I know, they will both be pulled on equally under load and you run the chance of running the smaller one bellow 3volts a cell(really bad for lipo's, can we say fire hazard). Personnaly, I would just get a bigger pack and a decent lipo balancer. Good luck with whatever you choose thoug.

brushlessboy16

straick is right. badddd idea

ASYSTEMERROR

run what you brung ?

speed racer 12

Yes, don't take the risk of running two different sized batteries at once, unless you know that you are doing

hemiblas

Ok, I thought about it some more today and talked to one of my friends and this is what we came up with. We think it will work and not have a problem. The battery with the less capacity will have a higher resistance and more current will flow from the larger battery with the lower resistance. Each battery will supply the current that it can and they will discharge at different rates. The weaker battery will discharge at a lower rate than the larger battery so running it below its voltage rating wont happen. Also if it does get to low, then the larger battery would act like a charger and charge the lower voltage battery(this would be bad though as the larger battery would now be working twice as hard and could burn out)

Even if what I listed above isnt true. Here is another theory.
One of the batteries will pull to much current and drop voltage, probably the smaller one. Once this happens the larger battery will kick in and deliver the needed voltage and current. More amps will flow from the larger battery until equilibrium is reached.

Basically I think this will work with any battery combo and the weaker battery will always supply less current than the larger battery. If I can get my hands on a lower capacity 14.8V battery I will give it a try and post the results.

Slo-V Flyer

I would experiment a little more about rigging 2 separate capacity batteries with Nimh or something less volatile and not to mention expensive.

Your theories might make sense on paper but more likely than not, the 2200 mah 20C (~44 amps) will supply about the same current as the 4400 12C (~53 amps) for a total of 97 amps constant up to a point. BUT the 2200 will drain down before the 4400 does, though it is possible the 4400 will kick in and deliver increased amps to either "charge" the 2200 or bear the entire current draw and be over stressed either way, all the while the 2200 will be near depleted....

Bad idea.

I wish Access or RURC would chime in more about running two different capacity Lipos with more accurate info.

J.D.T

slo v is right, the lower capacity pack get drained first and ruined in my experience.

hemiblas

You are right. The batteries would get depleted at approx the same rate because their current delivering capabilities are so close. That means their intenal resistance is about the same. If the smaller battery was only 10C, and had a higher internal resistance then it would drain at a slower rate than the 4400mah and both batteries would get depleted at approx the same same.

The problem lies exactly with what you pointed out. When the smaller battery runs out of capacity, it gets depleted and the larger battery has to carry the entire load of the motor and would possibly backcharge the smaller battery. The whole reason I was doing this was to save the larger battery from having to deal with that much stress, but it would just make it worst if the smaller battery gets drained all the way.

I was thinking if maybe a lipo cutoff would work, where the smaller battery cuts out before it gets depleted too badly. You guys are right though, the solution is to just get one good battery that works like its supposed to.

In the mean time I added a separate receiver pack for the radio and servos. Hopefully this will lessen the load on the larger battery, but I dont think its much.

Straick7

Your servos "might" draw 5 amps fully locked and high quality metal geared. I don't know for sure, which is why I say might. The motor on the other hand, as far as brushed goes, can pull around 40 amps running. The servos and receiver really are a drop in the bucket when you consider your overall amp draw of the system. As far as the lipos go, when you get your new ones, be sure that they can handle more current draw than the system is rated for to be on the safe side(don't want to overload them). That way the rest of the system will act like one very expensive fuse. One thing that I have seen done with lipos on car is the addition of a fuse between the lipo and the ESC, which considering the fact that you added a receiver pack, that actually wouldn't be too bad of an idea. Better safe than sorry, not to mention that it would be cheap insurance for your gear(you'd know what I mean if you've ever seen worst case scenario of a lipo overload). Let us know how it all works out for you.