Charging RC NiMH battery packs?

[nasukaren]

My Phoenix ESC arrived and my Boxer moped is up and running! I'm using as its main battery supply a four pack of 9.6V 3.8 Ah NiMH batteries that are designed for RC car usage. I currently have it as a 4S configuration (38.4V 3.8Ah) but will move up to a 3P 4S (38.4V 11.4 Ah) megapack when the rest of my batteries arrive.

I'm wondering what the best way to charge a 38.4V pack is. Right now I'm using RC battery pack chargers but they seem rather stupid -- i.e., the batteries are getting quite warm. I'm wondering if there is a good smart NiMH charger that can handle either 8 cells (9.6V) or 32 cells (38.4V). Does the group have any recommendations?


Karen

p.s. My Boxer blog is here: http://visforvoltage.org/blog/nasukaren/

 

[slayer]

well i hope you know it is dangerous to charge nimh in parallel, they should be charged alone in series of your choice
http://www.batteryspace.com/index.asp?PageAction=VIEWCATS&Category=337

edit.
and my nimh too get pretty warm it is normal to a certain point, some charger don t have in their algorithm the temp sensor and just cut after time period. so they could get a little warmer, it is the reason sometimes they say not to unplugged or wait a few minutes before recharging

 

[nasukaren]

Slayer-san

Thanks for the link but it looks like the biggest charger there is only 24V. It'd be nice if I could charge just one of my megapacks (38.4V or 32 cells in a serial config) at once. Right now, I'm unplugging the leads and charging two packs at a time.

Karen

 

[slayer]

i think i read somewhere that this one can do 32 nimh cells at once ...doctorbass knows a lot about this charger and could probably confirm, Sama.
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=6301&Product_Name=Mega_Power_Infinity-960SR_w/_Balancer_12S

 

[Miles]

Karen,

The Astro Flight charger will do a string of up to 40 NiMH cells:
http://www.astroflight.com/index.php?main_page=product_info&cPath=1&products_id=25

 

[Anonymous]

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[nasukaren]

Thanks all for the links! I'll try them out!

 

[jha07]

I'm doing almost the exact same thing as you nasukaren.
Except I'm using 7 cell packs. I have 5s 2p to give me 42V, 7200mah. I'm using a powerstream charger. They use a thermistor to detect peak and works great.

http://www.powerstream.com/NH2.htm

I've been charging in parallel with no problems. I have thermistors in both packs wired in parallel. This lowers my peak point so I don't get full charge, but also makes over charging of either packs impossible. I've found that both packs always get to the same temp anyways. I'm sure you can do the same in your 3P pack, but you'll need to add a resistor to the thermistor to compensate.

 

[docnjoj]

Knuckles is charging in a similar fashion with only thermal shut off as a monitor. Astroflight can charge 40 cells in series with only D/V cutoff.
otherDoc

 

[kefa]

what experience do people have of using rc nimh packs for ebikes?

i'm currently investigating battery options for my ebike project. rc lipo's look great but i want to be able to sleep at night knowing my house won't burn down. lifepo4 is too expensive given the current aussie exchange rate. there always SLA's if i'm desperate.

cheers,
keith