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Thread: Piggybacking a second battery?

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    Really Bored Monstyr's Avatar
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    Default Piggybacking a second battery?


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    I'm enjoying chugging about on my old sunbeam but until I get the alternator working properly I'm running a total loss system which will limit the range I'd like to explore.
    I've recently bought a little pannier style bag with the idea that I could carry a spare battery in it and if I discharge the fitted battery could run a jump wire from the spare to keep myself on the road.
    As an idiot with access to basic tools and little technical knowledge are there any problems in doing this?

    I know it's a stop gap solution and I'd really like to get the onboard system working properly ( it gives 3volts at the moment- but thats 3 volts more than it delivered last year, and I'm still treating it as total loss for now) but that is a home made set up that was never designed to work on this bike so until its worked out properly I thought this might give me options.

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    Default Re: Piggybacking a second battery?

    Absolutely no reason why not. Avoid idiot mistakes, like the optimate cable getting under the seat springs and getting cut...hence short to earth. A pratt on this site did that on an LE...don't ask who!

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    Default Re: Piggybacking a second battery?

    Quote Originally Posted by davidat19 View Post
    Absolutely no reason why not. Avoid idiot mistakes, like the optimate cable getting under the seat springs and getting cut...hence short to earth. A pratt on this site did that on an LE...don't ask who!
    Appropro a post in the bike bit ....I would love an S7 or 8.....but they are a bit too spendy.

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    Default Re: Piggybacking a second battery?

    The other thought is why not fit a new proper alternator? They are BSA items are they not? And have you tried a modern rec/reg? Mr Goff is the Man.

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    Really Bored Monstyr's Avatar
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    Default Re: Piggybacking a second battery?

    There isn't an option I can just bolt on, the OE system was a 6volt dynamo which never had a great reputation even when it did work consistently.
    I have a lucas stator and rotor, probably similar to what was put on lots of british bikes in the 50's and 60's, the old one had burnt out, probably because whoever fitted it didnt centre it properly. I've managed that bit and working out the rest will just be one step or change at a time until I get most of the bits working properly.

    I did read a good article where a kobuta tractor alternator had been used, though this required a bit of engineering know how to make it work, and I have neither the skills or the tools to do that so will need to work with what I have for the moment.
    I would actually like an original dynamo unit- or at least the casing for it but these seem to have become stupidly expensive in the last year so I'm not even looking at those any more.

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    Should Get Out More Yorick's Avatar
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    Default Re: Piggybacking a second battery?

    Fit a solar panel and leisure battery

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    Default Re: Piggybacking a second battery?

    Quote Originally Posted by Monstyr View Post
    There isn't an option I can just bolt on, the OE system was a 6volt dynamo which never had a great reputation even when it did work consistently.
    I have a lucas stator and rotor, probably similar to what was put on lots of british bikes in the 50's and 60's, the old one had burnt out, probably because whoever fitted it didnt centre it properly. I've managed that bit and working out the rest will just be one step or change at a time until I get most of the bits working properly.

    I did read a good article where a kobuta tractor alternator had been used, though this required a bit of engineering know how to make it work, and I have neither the skills or the tools to do that so will need to work with what I have for the moment.
    I would actually like an original dynamo unit- or at least the casing for it but these seem to have become stupidly expensive in the last year so I'm not even looking at those any more.
    Was it a miller or lucas dynamo? The cover from an le might fit.....

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    Default Re: Piggybacking a second battery?

    One thing I would do is to replace the flat battery with your spare, rather than just connect the spare across the main battery. The reason being that if you connect the spare battery across the main, the spare battery will just lose charge to the main battery - like finding a common level, as it were.

    I don't know Sunbeams at all - is the main battery in an awkward place?

    Edit: Do you have a link to the Kubota set up? Was it this one from Imp Barn? - Sunbeam S7 / S8 permanent magnet alternator conversion (recap)
    Last edited by Lutin; 02-05-19 at 09:26.

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    Really Bored Monstyr's Avatar
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    Default Re: Piggybacking a second battery?

    The battery is enclosed in a metal box so I'd need to sort out how the wires from a spare can connect but thats a fairly simple thing I think.

    The kubota article is on this blog.
    http://impbarn.blogspot.com/2011/12/...nt-magnet.html
    There was another article somewhere but I cant find that one now.

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    At Work iansoady's Avatar
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    Default Re: Piggybacking a second battery?

    I agree - if one has completely flattened then the pggybacked one will send all its valuable amps to that one rather than powering the mighty Lucas electrics.....

    It would be easy to fit a switch to isolate the main one.

    If you have all the original bits for the dynamo why not just fix that? They're fairly simple beasts.

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    Default Re: Piggybacking a second battery?

    Back in the 80s I had a Mini. Over the winter I used to take the battery out of my Moto Guzzi and connect in parallel to the mini battery. That way it kept the bike battery charged (a bit) and made sure the mini would start.
    Hers a link to some options. https://www.batterystuff.com/kb/arti...-tutorial.html

    Personally I'd go for iansodady option with an isolate switch. Or get it working better. Have you considered converting from 6v to 12v? I did with my DT175 and it gave a lot better options for bulbs and a much louder horn.
    Last edited by GuzziPaul; 02-05-19 at 14:13.

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    Default Re: Piggybacking a second battery?


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    Really Bored Monstyr's Avatar
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    Default Re: Piggybacking a second battery?

    It’s already a 12v system, I eventually plan to get the charging system working, I just need a ‘get me by’ solution in the meantime.
    I’ve taken the battery out of my ducati monster as it not on the road and isn’t currently needed, it’s a cheap option as I have it here, though it won’t fit into the S7 battery box so that’s why I will carry it separately and run it from a small leather pannier.

    some of the joy comes from fixing the crap others have already inflicted on the bike though that doesn’t always mean restoring it to its original configuration

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    Should Get Out More Screwdriver's Avatar
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    Default Re: Piggybacking a second battery?

    Just be very careful fitting any wires permanently to the battery. They need to be fused and routing needs to be very carefully thought through. Very common for a trapped wire to set fire to a bike if you're not careful. You really have to use a crossover switch as suggested above, you don't want to connect a charged battery to a discharged one for obvious reasons.

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    Should Get Out More Julian_Boolean's Avatar
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    Default Re: Piggybacking a second battery?

    A modern bicycle dynamo would probably provide enough electricity for a points ignition - they really don't need much.

    https://www.amazon.co.uk/Bicycle-Saf.../dp/B00RI9NQ5C

    or

    https://www.amazon.co.uk/Fischer-Dyn...sports&sr=1-17

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