can i parallel old and new Nimh?

[kefa]

What about adding some of these thermal switches to each of the battery packs?

http://www.goldmine-elec-products.com/prodinfo.asp?number=G14366

The pack that finishes charging first would start getting hot and should trigger the thermal switch to open and then the current would go to the rest of the packs. Still not ideal but would probably save the pack from exploding.

 

[heathyoung]

Yep - thermal fuses are CHEAP insurance - use them on the charging lead (rather than the discharge lead) or use a charger that does delta T (siliconchip electronics magazine had a design for one of these, uses a pic microcontroller and a thermister, backs off the charge current)

 

[icecube57]

My 12v Tenergy pack are OK. I have 4 permenantlly wired in parallel.

There is all this hype about not charging in parallel. I do it all the time. I do believe the pictures and everything but a well made pack shouldnt go into thermal run away. I just haven been a victim yet probably.

My Tenergy packs have thermal breakers in them that stop current from flowing on charging and discharging connectors when they trip. Ive wired two thermal probes inside the pack that disconnect from charger.

The other two chargers I place the thermal probe under the pack while charging. I have paralleled 4 chargers which were 2 different types of Tenergy Chargers with different charging styles. Burp/Discharge pulse and CC and CV. The pack only gets warm at the end of the charge time. The chargers terminate with in a minute of each other when they Detect the Delta V. The good thing about that is if one charger detects Delta V it terminates charge and the amperage drops and it causes the voltage to drop on the pack which signals the other to stop charging also.

THis is a supposed 16.8AH pack. I charge at about 10A so that .6C.

I think you can charge in parallel if each pack or sub pack has its own safety features in place to help protect the pack.

It will also help if the pack were freakin matched too. After exercising my packs I charged all my packs individually to the same voltage assembled them together.

IF you dont match them the packs with the higher voltage will more likely have a lower internal resistance so when you charge them the current will flow to an already charged pack. But if the pack has a thermal breaker. It will trip and block current from flowing into the pack and allow the others to catch up and when the breaker resets the other packs should be in closer resistance to where its not an issue again and they will accept a charge evenly.