How Do You Bake a Battery?

Yesterday my packs were installed. Two 24V 18Ah NiMH Nexcell packs connected in series.
They're for the Xtracycle. I had them padded inside the Xtracycle's bags with some extra clothing and chunks of styrofoam when I discovered they could hit against the frame. Denting the brand new cans would have a disaster.I rode home gently and started to work on protecting the batteries from damage while temporarily carrying them in the Xtracycle's FreeLoaders.

Last night I wrapped them in coroplast and strapping tape to protect the cans. This morning I wrapped that in 6mm neoprene and hockey tape for more protection and stealth. As I was finishing up it occurred to me that it probably was a bad idea and now I'm afraid to charge to them.

The packs will be charged separately with 24V 4A chargers from Nexcell.
Given an air temperature of 72F, my question is will the heat rise inside the insulated packs cut off the charger before reaching full charge?
I have a digital thermometer with a probe that can be inserted through the neoprene. Given that the pack is also insulated by the coroplast what sort of temperature should I be looking for as approaching the danger zone that could affect the batteries' longevity?
Comments?

At $950 per plate, I can't afford to eat fried, or baked, guinea pigs.

Wow, coroplast, tape, neoprene, and hockey tape? I wouldn't be surprised if the charger stopped before they actually got a full charge, especially with a 4A charger...

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Link said:

Wow, coroplast, tape, neoprene, and hockey tape? I wouldn't be surprised if the charger stopped before they actually got a full charge, especially with a 4A charger...

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Back to the drawing board, eh?

Oh well, they sure looked pretty.

How about heat sinks glued to the shrink wrap on the cells' ends? Then the coroplast and neoprene are cut out so the heat sinks radiate to the air?

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nutsandvolts said:

FWIW I had the same concern about batteries bumping up against the xtracycle frame. However, my batteries are already inside ruggedized enclosures since they are tool batteries. . . . Long term, I want to move the batteries lower, and brace them to the xtracycle frame with custom metal bars.

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In addition to the coroplast and neoprene cookers, I hockey taped pipe insulation to the frame members where the batteries were making contact.

This is roughly where I'm planning to place the batteries. Riding today I missed the cargo space occupied by the batteries. Placed ahead of the axle they conflict with the passenger pegs. I had enough cable to slide them back and that worked okay with the passenger's greater weight being forward.

Thnaks a bunch, guys.

I'll be cutting off all that work I did and strart charging now.
Tomorrow I'll just wrap them in 12mm neoprene and inner tube strips.
Wrapping and unwrapping them for charging will get old fast so should spur me toward a better solution.

The pack themselves will need to be opened and the arrangement of the cells changed to fit in the frame spaces where I want them.

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The cells really don't get hot during the majority of the charge, only at the very end do they heat up. As long as you allow the packs to cool down before plugging in the charger ( of course, this will take longer so if you do not have alot of time between end of ride and start of charge,, could be a problem )

As long as you don't push the cells to more than 2 C, and run them at 1C the majority of discharge they won't get very hot during discharge either.. at 2C continuous they do bake quite alot..

tough call.. :?

Ypedal said:

The cells really don't get hot during the majority of the charge, only at the very end do they heat up. As long as you allow the packs to cool down before plugging in the charger ( of course, this will take longer so if you do not have alot of time between end of ride and start of charge,, could be a problem )

As long as you don't push the cells to more than 2 C, and run them at 1C the majority of discharge they won't get very hot during discharge either.. at 2C continuous they do bake quite alot..

tough call.. :?

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Thnaks even more.

The battery packs, in all their heat shrink nakedness, are sitting on a chunk of heavy aluminum 3" channel while charging.
I'll keep monitoring them and see what kind of temperature they reach during the conditioning/charging/resting/supplemental and trickle charging sequence.
The instructions say the charger shuts off if the cell temps reach 53°C.
I'll be able to tell how much the outside end cells temperature increases.

The insulated cases I'd made came apart nicely enough that it looks like they can be reused if the batteries will cooperate.

The charger should shut down before the pack hits 53c, it will detect temp rise or peak voltage, the 53celcius cutout is in the event of an emergency with something really wrong going on lol..

When i was running 72v 8ah ( 2 x 36v nexcells frome bikes.ca ) i had a high power fan blowing on them during the entire charge cycle, i found that the pack would slightly overcharge before the charger kicked into trickle mode, i then later started charging the pack, letting the charger to " Green / trickle " and then turning on the fan to cool down the hot packs..

If this makes any difference for cycle life i have no clue, but it's how i did it and they ran just fine for 2 years, sat on the shelf 1 year, i cycled them and bench tested them after this period and they had full 8ah capacity left and are still in use by one of my customers to this day. :wink:

Back when I thought my battery would fry before my motor, I was concerned about heat, so I packaged my ping pack in a box made by cutting the corners and folding a cookie sheet around the pack. It heat sinks ok, much better than bare duct tape, and saved the pack when I crashed. It's cheap and simple. I ended up with a sort of custom sised bread pan for the pack.

Well I'm glad I unpacked the batts before charging them because there was weirdness right from the moment they were plugged into the chargers.
Both chargers did their 4 second self check successfully.
When pack A was plugged into charger A the fan came on. According to the instructions it's not supposed to run unless the charging chamber temp is > 30°C
When pack B was plugged into charger B the fan remained off. Okay. They both were showing the appropriate LEDs for the conditioning and main charge.
Charger A showed its blinking green light when expected. The blinking green on Charger B didn't come on but the fan did. Neither battery pack or charger was what I'd consider excessively warm.

I woke a few times during the wee hours to see the progress. The only time a saw a blinking green light on charger B was when it was blinking in conjunction with the yellow light blinking indicating the battery temp is abnormal. That pack was definitely warmer than the other. Charger A had shown a steady green light for about 6hours when I unplugged both packs.
Pack B or charger B seems to have a problem. I hoping it's just a thermistor or something cheap.

After cooling down it read 27.9V and batt A read 28V. Five hours later it reads 27.7V and batt A reads 27.6V

I don't think anything got cooked but tomorrow I'm going to ask Zev what's going on.
Maybe tonight I'll try batt B on charger A but that means having to go out into this beautiful weather and run the packs down again.
That's sounds like too much fun so that's what I'm doing as soon as the laundry is done.

dogman said:

Back when I thought my battery would fry before my motor, I was concerned about heat, so I packaged my ping pack in a box made by cutting the corners and folding a cookie sheet around the pack. It heat sinks ok, much better than bare duct tape, and saved the pack when I crashed. It's cheap and simple. I ended up with a sort of custom sised bread pan for the pack.

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ohhh, bake ware! How appropriate.

I can't find any aluminium baking sheets or pans except the disposable type. They're all steel.

Thin aluminium for roofing patches or something is sold in rolls at Canadian Tire and Home Depot but it doesn't look like it would offer much protection.
A small bench brake and shear would be handy for recycling computer cases into battery boxes.

Try the trift stores for a baking sheet. In my town Home depot has aluminum diamond plate, but the baking sheet was so much cheaper.

dogman said:

Try the thrift stores for a baking sheet. In my town Home depot has aluminium diamond plate, but the baking sheet was so much cheaper.

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I've been looking for aluminium bake ware at the local Salvation Army store since an earlier thread mentioned loaf pans for battery boxes. My plan is to use one as a rain shroud for the controller. Tread plate seems like it would be kinda hard to bend on a Workmate.

What do you use to isolate the aluminium from the battery? Seems like a bad idea to trust the shrink wrap considering vibration and road shocks. I know hard rubber transmits heat better than neoprene. I can occasionally access both from a gasket makers dumpster bin. There's a scrap metal dealer closer to my home than Home Depot. It might a good idea to check there first.

The ideal battery box will have to fit the frame spaces. Provide a high degree of theft deterrence. Be water resistant, allow ventilation and heat transfer while also insulating against electrical shorts, vibration and crash protection. Switches, fans and charger plugs to simplify the charging process add complications.

I've put 75 kilometers (45 miles) on the last charge and the CA indicates there's still 50.1V in those two 24V packs.
The combination of the 18Ah NiMH packs and 5304 has thus far perfectly met my criteria. Up a bitch of a pitch, that I'd avoid with a load, at 20KmH, I can still accelerate with passenger aboard. That's what I wanted

I like travelling at bicycling speeds on a bicycle. Rolling this heavy, long wheel base, upright is a joy. On the flats, the throttle is off. There's no point in blowing watts to the wind. My max speeds are achieved coasting. I'd feel cheated of a bike ride if I wasn't pulling chain and getting into the aerobic zone.

8)

I did an extra wrap of duct tape on my pack before I bent on the aluminum, and made the corners so there were no sharp edges facing in. It fits so tight, rubbing just doesn't happen. Then the bake pan goes into my toolbox bolted to the bike, and can rattle around there all it wants with no problems. Some foam wedges hold the rattling down to a minimum. The cookie sheet was perfect since it bent so easy. I pretty much folded it around the pack with bare hands.

Regarding heat transfer: Steel is pretty good for transferring heat. Just avoid Stainless steel. It's thermal conductivity is really low, similar to many plastics.

Marty