Extension battery 2x Diodes or 2x 2way switches?

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Heman B.
Joined: 05/18/2012
Points: 102

Extension battery 2x Diodes or 2x 2way switches?

Postby ProDigit » Fri May 25, 2012 2:55 pm
Hi all,

I'm thinking of extending my e-bike's range by buying an extension battery.
There are 2 possible solutions to connect the extension battery. Via diodes or via a switch.
Via diodes I can connect both batteries in parallel. But the voltage drop of batteries lowers the more batteries are connected in parallel, meaning the controller won't shut down, until the batteries are really really empty (which is bad for battery life); and there's no way of knowing when the batteries are empty, until they are (since the battery level indicator will only drop when both batteries are already below their lowest charge).

With a switch it's somewhat safer. have 2 switches installed. Drive on the first battery, until it gives in. Switch to off. Switch the second battery on, drive to stop.
Now you know that both batteries are empty, and if you're still not at your destination, then there's no alternative than to switch both battery switches on, and drive with batteries in parallel.
Advantages of this setting is: no voltage drop of diodes.
Disadvantages: if the controller shuts down in parallel mode, the voltage per battery pack will be even lower than with diodes. One could literally drive both batteries dead, especially when one forgets to disengage the backup battery pack!

1- Diode: but the guy making the diodes, specifically made for bikes, does not make them anymore; So I thought of going on amazon to find one, and I found these:
http://www.amazon.com/D92-02-Integrated ... 81&sr=1-55
Instead of buying a 10-pack of 6A diodes that I'll have to solder together in parallel, I just thought of getting two of these (one for each battery's anode).

The only issue with these is that they look like a transistor!
They have 3 pins instead of 2. I don't know which pins to choose, as a diode usually does not have a gate. I suspect one of the pins is a grounding pin?

2- Switches:
I haven't yet found tiny switches that are easy to install and can handle 20A, if not I'll have to go with regular lightbulb switches,and hope they can handle the current.

3- Connection:
I'll also have to figure out a way to plug and unplug the extension battery from the bike for charging purposes.

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