Keeping those Nimh batteries cool!!!!

[joystix2]

I've noticed since I stuffed my 48v13ah Nimh pack and controller into a trunk case on my bike my range has suffered. Before I had them just mounted on the rack by velcro and bungees and was getting 15+ miles on my commute. Yesterday, going the same speed as before I got to around 11 miles and noticed the voltage drop on throttle up was significantly lower (35/37v compared to 41/42norm). And thats with peddleing at start ups. After my ride home my total miles was 12.2 and final voltage was only 45v after settleing in about 2 minutes. The pack and the controller were very warm to the touch. I always keep the bag unzipped and opened partially on top to help with cooling but it's not enough. Tomorrow I will run my commute with the old style bungee/velcro system to see if the range goes back. Or maybe it was just a bad charge. I really like the stealth look of the trunk case so i'll have to add fan forced cooling to the batts and controller.

Anyone else have the heat problem with using a trunk case? If so what are you doing to keep things cool?

Ric

 

[NickF23]

I've got a couple of hatches I made with screw caps from plumbing parts, i leave them off nearly all the time but close them in very heavy rain/when the bikes parked up in rain. keeps them nice and cool.

 

[knightmb]

My NiMH pack gets warm after a long ride as well. Before, I had the controller and batteries in the same bag. The problem was, the controller would generate so much heat that it would hit the thermal cut-off and the bike loses power. The batteries were insanely (almost scary) hot when this happened, so I moved the controller to behind my seat within "splatter" distance of my back wheel. That was the main heat problem for me. Now I can ride and the batteries only get a little warm, not near as bad as before.

It helps in the winter time to keep the batteries warm, but in the summer time it becomes a power sink to your range. Got any links or pictures to your e-bike?

 

[safe]

Good to know. (about heating issues)

I'm thinking about designing a bike with the batteries INSIDE the frame. Using square rather than round tubing I can get them in there for about the same amount of space, but the difference in the shapes creates a natural air passageway that would assist in cooling. Sounds like this idea is a good thing to pursue. I'm planning on still having the batteries "spring loaded" and not soldered, so I can remove and check them periodically. It also frees up more space for other things. This picture would be the cut away "cross section" of one half of the frame of a "Deltabox" design.

 

[knightmb]

I think it's an excellent idea. Otherwise, they will be "insulated" inside the frame, and too much heat is certainly the enemy of the battery. I'm not sure how much heat the metal of the frame would conduct away, so maybe the square frame is just a good measure for safety when you build it. Can even use the space for wires

 

[safe]

Can even use the space for wires

Yeah that is a good thing too. That way it can be very clean looking from the outside. The square tubing would be welding in long welds along the seems on the edges, so the middle of the tube should not be disturbed. It would make a very strong "Deltabox" frame because it's basically "honeycombed" inside.

 

[joystix2]

KnightMB,
Heres the link to my build. I will be updating it shortly.

http://endless-sphere.com/forums/viewtopic.php?t=363

Ric