Back-up Battery for e-bike?

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Ian
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Joined: 07/21/2007
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Dear forum members

Can anyone advise on how hard/easy it is to install a back up battery for an ebike that can be switched on/off at the handlebars? ie, can it be done and if so what would I need in regards the wiring?

I am running 36v 13ah nimh as my main battery and had in mind a 6v battery that I can add to the main pack at the flick of a switch at certain times - say on hills when the voltage sags, or on the final leg of a long ride. I am not able to add a 6v battery permanently as the peak initial voltage would be too high for my controller.

Thanks
Ian

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reikiman's picture
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Re: Back-up Battery for e-bike?

Why would you want a battery that can only be used for backing up? On a bicycle don't you only want to move forward? It doesn't make sense to drive backwards on a bicycle.

oh.. wait.. I read your second paragraph. Hmm, you mean like a reserve tank. Yeah what you're suggesting should work. So how would you do it?

It's probably a bad idea to run your full pack voltage through switches on the handlebars. So it might be best to have relays to do the job, and control the relays from switches on the handlebars.

I just drew out a diagram and think it's a simple matter of a single-pole-double-throw switch. You'd wire the pack as -B-B-B-B- (four batteries in series) and the switch selects whether to tap the pack from between battery 3 or battery 4.

The most interesting consideration is ... will the switch handle the current you're running on this bike. Will the current weld the switch shut to a specific setting? It's probably best to make sure you're NOT running current when you switch the pack configuration. And make sure to get a beefy enough switch that the rated load is well above what your bike runs at.

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jdh2550_1's picture
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Re: Back-up Battery for e-bike?

When looking for a beefy switch check out marine supply places - hardware stores don't carry high amp DC stuff but boat places do.

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reikiman's picture
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Re: Back-up Battery for e-bike?

check out marine supply places

Yes, good point. I have visited the local West Marine so much they talked me into joining the boat owners club so I get discounts. I don't own a boat, but I figure their stuff is meant for "Weather" of a sort we landlubbers can only dream of, so it's got to be good for use on a bicycle that's gonna get rained on. Plus they do carry some heavy duty wiring and switches and stuff.

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- David Herron, Green Transportation Examiner, Green Transportation Info, The Long Tail Pipe, Torque News, electric race news, davidherron.com, 7gen.com, What is Reiki
- EVT 4000, Charger bike (rebuilt), Vego 600sx (rebuilt), Electrified Electra Townie
- Lectra motorcycle, 1971 Karmann Ghia

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