Double your battery life

[DickB]

Take the battery off the bike, turn it on, probe the terminals while it is charging.

[natchezz]

Thank you, DickB! I will try this on my next charge. I always remove the battery and charge it on my workbench in my basement.

If you knew your battery's starting voltage, could you calculate how long it would take to reach 80%? You could set a timer on your phone to go test it then.

I would be interested in buying your smart switch if you start selling them.

[DickB]

While the smart switch works, I am using my much simpler diode device. It lowers the float voltage to the 80% charge level and requires no monitoring - you just use the charger as usual, and the charger can be left on indefinitely. You could estimate charge time to 80% knowing the starting voltage, but why bother?

[natchezz]

You could estimate charge time to 80% knowing the starting voltage, but why bother?

Anyone with electronics fabrication tech skills care to sell me a diode device?

[DickB]

The parts are relatively inexpensive, but I got parts from multiple sources, so shipping costs can add up. I'd consider making a small batch if there is sufficient interest.

[natchezz]

DickB, in a prior post you mentioned having to upgrade the diodes due to heat issues. Was that for your smart switch or diode device, or both? Are you recommending 4 diodes instead of 2 in the diode device for closer to 80% charge?

[DickB]

Diode device. 4 diodes. I posted parts list.

[MikeC]

The parts are relatively inexpensive, but I got parts from multiple sources, so shipping costs can add up. I'd consider making a small batch if there is sufficient interest.

I can solder, but it ain't pretty. If you're keeping a tally, I'd buy two (one for both myself and my wife).
Mike

[RiderDan]

Don't you have to be mindful of how the battery BMS balances the cells in the pack?  From what I've seen, different BMS's will start their balancing stage after different charge voltage thresholds.  This is one of the reasons why Rad Power recommends leaving the battery charging for up to 12 hours on the first initial few cycles.  If you consistently charge up to a specific lower voltage and that voltage isn't high enough to trip the balancing mode of the BMS in the pack, you run the risk of throwing the cells out of balance and causing big fiery problems down the road.  Have you looked into how the BMS on the Rad batteries balance the cells?

-Dan

[DickB]

The Rad BMS enables balancing based on voltage difference between cells, not a specific cell voltage or charge voltage. Balancing is enabled when cell voltage is between 3.3V and 4.45V (42.9 - 57.8V float voltage).

Rad uses a Sino Wealth SH367008 chip in the battery BMS. The numbers are from the chip spec sheet.

The chip uses passive balancing during the charge cycle only. Shunt resistors bypass charge current past the higher-voltage cells to the lower-voltage ones. The Rad charger Charge light turns green when current to the battery drops below about 200 mA, but small current continues to flow. That is why the charger is left on for 12 hours, to permit the balancing current.

[DickB]

To clarify, the smart switch will cut off current before balancing, and if used would require charging to 100% without the switch for 12 hours every month or so. That is one of the reasons that I switched to the diode circuit. The diode circuit limits float voltage to the 80% charge level, but does not shut off charge current and does enable balancing.

[RiderDan]

That's a perfect clarification!  Thanks!  👍👍

[natchezz]

The parts are relatively inexpensive, but I got parts from multiple sources, so shipping costs can add up. I'd consider making a small batch if there is sufficient interest.

What's your idea of a small batch? Including one for me, I think you're up to 3.

Any other takers out there for one of these diode device units? Please speak up!

Maybe it needs its own thread?

[DickB]

I will put together a parts cost spreadsheet and see what quantity makes sense.

[DickB]

Parts cost to me is $25.18 plus shipping.  I'd build 5 and sell for $40 each plus shipping ($8 for Priority mail in the US).