Charging auxillary battery

cyclistbruce · Derestricted Danger Joined: 02 Aug 2012 Karma :

Hi,

I've for an 07 Honda ST1300. I'm looking at installing a small 1.7ah 12v lead battery to run some auxiliary emergency lights that need to be able to work when the power is off, without draining my main battery.

My plan was to install the battery in the left hand fairing box and connect both batteries to the alternator with a splitter like this:

https://www.maplin.co.uk/p/kemo-lead-acid-battery-split-charge-module-n73au

The auxiliary battery won't actually be used that much, and is just going to be used to drive LED strobes. Does this sound like the best way of doing it, or should I just connect the batteries in parallel?

Cheers,

davebike · World Chat Champion Joined: 15 Nov 2013 Karma :

Split charge Is good Or
Supplying the charge from switched power so charging stops and starts with bike engine
Engine running small battery charges and what it powers runs off power from bike
Engine off no connection to bikes electrics

Dave
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jjdugen · World Chat Champion Joined: 03 Jun 2011 Karma :

20p diode from Maplins. Where I show a feed to ignition system, you connect to your auxilliary system. When the bike is running, the alternator charges the main battery normally and the aux battery via the diode. Once the engine is switched off the aux battery can discharge without affecting the main battery as the diode blocks the voltage from entering the main system.
(I use this for high drain starters, Ducatis, Guzzis.... and Laverda Jotas, it leaves the ignition system isolated from the spikes and voltage sags of the main battery under these extreme conditions.)
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cyclistbruce · Derestricted Danger Joined: 02 Aug 2012 Karma :

Blimey, that seems a lot easier than I thought! What mm cable do you use to take the power to the aux battery?

jjdugen · World Chat Champion Joined: 03 Jun 2011 Karma :

Just use your bikes standard wire. The only place that uses the thick stuff is the high amperage supply side to the starter unit.
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sickpup · Old Timer Joined: 21 Apr 2004 Karma :

davebike · World Chat Champion Joined: 15 Nov 2013 Karma :

St1300 has a massive alternator something like 750W /60 amps A don't think you have a problem charging via a diode

Dave
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Biker Dave · L Plate Warrior Joined: 16 Mar 2014 Karma :

I think you'll find that using a Diode as shown in that drawing will allow the main bike battery to be drained along with the aux battery when the ignition is switched off.

A split charging system is the best way to go.

davebike · World Chat Champion Joined: 15 Nov 2013 Karma :

A diode wired so as to let power go to the aux battery will not let it return
A diode only let power go one way (OK there is some leakage but pico amps )

Diode will need to be quite large as inrush current will be big at least 10 Amp

Dave
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Polarbear · Super Spammer Joined: 24 Feb 2007 Karma :

hmmmnz · Super Spammer Joined: 22 Aug 2006 Karma :

just a cheapo relay will do the job,
disconnects when the bike is turned off, and connects with the ignition is on, very basic and works sweet as,
its how i charge my "house battery" on my merc camper,
never had a flat starter battery on my travels throughout europe

https://www.bikechatforums.com/download.php?id=92206
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sickpup · Old Timer Joined: 21 Apr 2004 Karma :

davebike · World Chat Champion Joined: 15 Nov 2013 Karma :

As long as it is also Lead acid so charging should be voltage limited no problem with over charging as it is just in parallel with the main battery so cannot have more volt across it than that Battery so unless that is over charging no problem

Dave
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cyclistbruce · Derestricted Danger Joined: 02 Aug 2012 Karma :

I've just noticed that the blurb for the split charger states that it is for charging currents up to 10A or 20A if cooled? Doesn't a ST1300 alternator supply something like 60A, so presumably I'd melt the splitter?!

Polarbear · Super Spammer Joined: 24 Feb 2007 Karma :

cyclistbruce · Derestricted Danger Joined: 02 Aug 2012 Karma :

So I've got myself a diode and a relay and will decide which one to use when I take the fairing off. With regards to the diode, I've got a 6amp rated one, but will that not be rated high enough?

If I use the relay, is the switching feed from acc just going straight to ground? The auxiliary battery is significantly smaller, 1.7ah sealed lead aciod. Is there any chance this will.overcharge?

cyclistbruce · Derestricted Danger Joined: 02 Aug 2012 Karma :

So I've connected the relay and it all seems to work, one concern that I have is the potential for overcharging. The aux battery is much smaller, (1.7ah), I don't really understand how the battery 'stops' charging when at full charge?

davebike · World Chat Champion Joined: 15 Nov 2013 Karma :

Lead acid batteries are charged using voltage limiting
Bike charging system is voltage limited therefore your addition battery will get the same or possibly slightly less charging voltage
no problem

Dave
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cyclistbruce · Derestricted Danger Joined: 02 Aug 2012 Karma :

Thanks!