6cell/7cell charging question

[devestator_x]

Ok here's the scenario. I just bought my first AEG Airsoft gun. It runs on 8.4V. Since I didnt have any 7cell batteries for it and none are included with the gun, I decided to make one. I had a few 6cell NIMH's for my RC trucks and one had a known bad cell. Here's what I did. I cut a few plugs, opened up the bad pack, removed a good cell, soldered up the plug ends and made what is essentially an inline single cell pack. It can piggyback in line with my 6cell packs and increase voltage to run the airsoft gun. With a multimeter, everything checks out great, gun fires great, yada yada....here's my question/concern. Since my 6cell pack is not fully charged and neither is my single cell, is hooking them both to my digital charger going to over/under charge either pack? I cannot charge them separately since the single is inline (positive leads only, negative goes straight from plug to plug)

I forgot to mention, all my packs were/are identical Duratrax Pirhana 3000mah, so it's not a total mismatch in quality/runtime/voltage/etc. I just dont want to burn up the single cell since the currently stored mah is different than the 6cell's currently stored charge. I guess on a good note, if things go bad, I still have 4 other single cells to mess with.

[constantmotion]

You may want to discharge the newly assembled battery all the way by hooking a light or something up to it.

[devestator_x]

So plug them in together to create my 7 cell pack and then discharge them completely before charging them. I thought completely discharging NiMH's was a big no-no.

[CreepyCrawl]

Originally Posted by devestator_x

So plug them in together to create my 7 cell pack and then discharge them completely before charging them. I thought completely discharging NiMH's was a big no-no.

On the contrary; discharging helps to revitalize the cells. A member of the community here once told me that every 12th cycle or so, it's a good idea to discharge NiMH cells and then bring them up slowly at a low rate. This is said to help extend the overall cycle life and performance of the pack and keep the individual cells in good shape.

Electric racers would regularly dead-short packs and then charge them at very high amp rates to give the packs the most punch possible. Not needed as much with Airsoft, but I think you will see a performance improvement by implementing this process as well. This will not yeild the longer cycle life like the previous method, but it may make your weapon of choice a bit more potent.

As far as your particular pack, I'd agree with Constant here and equalize all the cells before your initial charge. It certainly won't hurt.

[devestator_x]

Thanks for the replies. I have an email out to Duratrax as well, Im curious as to what they will say. Probably not to do anything, throw that stuff away and buy one of their pre-made 7cell packs

[floogldood]

The cells must be at the same SOC before charging or discharging.

If they are discharged as a 7 cell pack and the single is at a lower SOC then it will be reverse charged and get hot quick, may be damaged. If they are charged and the single is at a higher SOC than the other 6 then it will be overcharged and get hot quick, may be damaged.

You can equalise them either at the discharged state or the charged state.

D run the 6 cell pack dead in your truck of with a light bulb , do the same with the single cell. Then charge normally.
C charge the whole pack as is at c/10 for 15 hrs. Then use it normally.

[devestator_x]

So Duratrax/Hobbico wasnt too helpful...

Thank you for contacting Product Support.

If the cells are all the same capacity you should be able to charge the pack as a 7 cell.


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I knew that part. Anyway, Im thinking of just making a "jumper" plug to complete the circuit on the single cell and charging it seperatly. Seems like it will make the least amount of hassle.