Power cuts off on medium grade hill

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thehermit2
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Power cuts off on medium grade hill

I've been riding a Merida 550 back and forth to work for about 4 years (9 mile round trip). I've hit a unique problem after purchasing a NIMH battery pack to replace the SLA packs I'd been using. I bought a 26.4V 13Ah pack (22 1.2V F cells) from batteryspace.com. When I plug the new battery in, it powers up okay, and it will ride okay for short distances over level terrain. However, when I try to tackle a medium grade hill (one that requires switching to speed 2), the power mysteriously cuts off. A few seconds later it will power back on again as if I just turned it on, and I can ride around on level terrain again, but trying to tackle the hill will cause the power to cut off again. The fuse doesn't blow, and there are no sparks; I'm just losing power. There don't appear to be any loose connections on the battery pack itself, and the consistency with which it happens make me think it is something else. I also have a second battery pack (25.2V 10Ah, 21 1.2V NIMH D-cells) that worked okay before and still works okay after, so there aren't any loose connections on the bike itself. I experimented with removing one of the F-cells (down to 25.2V) and then a second (24V) and I still get the same result. The only thing I can think of is that there is a loose connection in the battery pack that I missed or that something in the bike doesn't like the amperage, although in the past I wired up a 24V 20Ah SLA pack successfully.

Also, for anyone else thinking of trying one of these packs, the Powerizer 26.4V 13Ah battery pack from batteryspace.com is about 1/2" too wide to fit in the original Merida battery case. I managed to barely sqeeze it in by drilling out portions of the case, but I wouldn't recommend it.

andrew
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Re: Power cuts off on medium grade hill

It could be cell interconnects. You can maybe feel the end of the cells. Heat will indicate a high-resistance point. Maybe take it to batteries plus or a local battery dealer, and have them add some spot welds.

Otherwise, one of the cells in the pack could be bad, and adding a lot of resistance.

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thehermit2
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Joined: Saturday, March 15, 2008 - 04:29
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Re: Power cuts off on medium grade hill

Thanks for the advice. Still no luck, however. There is no indication of heat on the battery ends unless it dissipates in the time it takes me to stop the bike and check.

I tested each of the battery cells individually, and while most hovered around 1.31 volts there was one that was at 1.26. I removed it from the circuit and tried again, but I still had the same mysterious power loss.

About all I can think of now is to take it to a local battery store and see what they can find. I'm afraid that the work I've done on it has invalidated the warranty.

andrew
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Re: Power cuts off on medium grade hill

Can you do a load test of each cell? One bad cell might not register a low open circuit voltage. A thin strip of aluminum foil can be used to apply a load to one cell at a time while measuring the voltage but be careful. It'll get hot!

They could all just be a bit weak until cycled 2-3 times. Since you have a digital multimeter, I assume that you've checked to make sure the charger is charging the batteries. They could be drained on the bench and charged a couple times to see if that helps.

They could just have a high internal resistance. In that case, just add cells in series to the pack. If the charger can't charge a larger celled pack, than you can get a different charger to charge the extra cells. Add one cell at a time until the cutout problem goes away.

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kjslough
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Last seen: 10 years 6 months ago
Joined: Thursday, July 10, 2008 - 07:43
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Re: Power cuts off on medium grade hill

i have a batteryspace.com pack that does the same thing. It is a 24V, 10 Ah that is only rated for 10 amps current. If I draw more than the rated current for too long a period of time (like more than 5 or 10 seconds), then the temperature sensor in the battery pack shuts itself down. After it cools off sufficiently, it comes to life again.

i ended up wiring two of them up together as a single 24V 20Ah pack rated for 20 amps which worked better.

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