# Battery back up

## Main Question or Discussion Point

I currently have a set up where I have attached a permanant magnet dc motor to a bicycle. The motor is attached through a diode to a 12v regulator and then to a 12v to 240v inverter. Everything works fine and I can power up my devices.

But I have been told that if I connect my 12V lead acid gel battery to the inverter as well via a diode, this will act as a back up source, so if I stop pedalling, the battery will power the inverter via a process called forward/reverse biasing.

Please can I get some advice on this and whether it will work?

Thanks

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berkeman
Mentor
Thank you for your reply, that was a really positive answer for me. I have a reulator in the circuit too which outputs 12.5 volts. Does this mean that the inverter would constsantly run off my battery?

I was thinking of charging the battery by simply making a constant current charger using the lm317. Would you reccommend this? Also, this would not effect the process of the inverter using the highest voltage from the two dc sources would it?

Thanks
Mitul

berkeman
Mentor
If your generator is not running, and your inverter is still connected, then yes, it will draw current from the battery and/or charging circuit. If the charging circuit cannot supply what the inverter will draw, then the battery will be getting discharged some.

Thanks for your reply. What I intended to say was that my generator is regulated to 12.5 volts. Does this mean that voltage will be drawn from the battery as I have read that the battery gives out approximately 13v and the inverter draws from the source providing the highest voltage. Sorry for asking such questions, I am just trying to understand how this would work.

Thanks

NoTime
Homework Helper
The battery will produce close to 12v with a load on it.
However, charging voltage is usually about 13.6v.

Given that most 12v inverters a designed to operate connected to a car, then this voltage swing shouldn't present a problem unless you have an unusual inverter.

All you should need to do is connect the battery to the inverter/regulator output junction and adjust the regulator to charge the battery.
You might want an indicator to show you are pedaling hard enough to keep the battery from being discharged.
Do some reading on automotive charging circuits.