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I recently replaced the cells in my ebike which consisted of 20 Ni-CD Size D (1.2V) 4,000mAh with 20 Ni-Mh Size D (1.2V) 10,000mAh batteries.

Before installation, I charged up each battery to ensure it was working, and connected the cells exactly how the old cells were connected. I tested the battery on the bike and it ran beautifully.

However, when it came to charging the battery, it simply would not charge. I can confirm the charger was working with the previous cells, but since I’ve changed them, the charger only shows a green led. The charger that I am using is rated for Ni-Mh batteries and is 24v 1.8A.

Are some built in protections preventing it from charging and is there anything I could do to get it charging again? I was looking at various chargers online with a similar rating but am unsure if i purchase one, if the same issue would arise.

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    \$\begingroup\$ maybe the old "charger" is only a power supply. the charging circuit is built into the ebike and it is not designed for ni-mh cells. \$\endgroup\$
    – jsotola
    Oct 31 '17 at 7:05
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    \$\begingroup\$ There weren’t any circuit boards within the battery pack, though it did have something that looked like a resistor. Other than that, it looked like a straight connection to the charger, which is why I am stumped. The connector is a 3 pin inline connector, so I’m not sure if this resistor (if it is that) is giving a “signal” to the charge adaptor not to charge, so as to prevent overcharging. \$\endgroup\$
    – vPete
    Oct 31 '17 at 7:25
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    \$\begingroup\$ It sounds like the "resistor" is essential to its operation, maybe its a temperature sensor. Manufacturers don't usually use a 3 pin connector when 2 will do. Do you have a photo of the resistor? \$\endgroup\$
    – Steve G
    Oct 31 '17 at 8:40
  • \$\begingroup\$ Just opened up the battery to have a look at the part and found a few other things. So the positive wire connects first to; 1. diode (in5822) - its a Schottky Rectifier photos.app.goo.gl/xEa7G2Gw3WUCGz4H3 2. It then connects to Klixon battery protector (ys11a80a) which appears to be a thermal cut out protector. photos.app.goo.gl/3uHal4ZNU4pm2Pop2 3. then it connects to the battery \$\endgroup\$
    – vPete
    Oct 31 '17 at 12:52
  • \$\begingroup\$ Thing is, if it is a thermal protector, it seems strange as the ac adapter does not charge as soon as it’s plugged in. So if it was a thermal protecting cutoff, wouldn’t it at least charge for a bit? \$\endgroup\$
    – vPete
    Oct 31 '17 at 12:52
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I managed to fix my issue. Purchased a NIMH 20cell charger form ebay and had it connect up to just the positive and negative wires. Still not sure what the 3rd wire does, but bike now works and charges well.

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