Battery for a GT500

[buzzer]

Hi guys,

I am building a GT500 cafe racer and concidering putting the battery in the seat hump. What is the smallest battery i can get away with?

[Zunspec4]

It would depend upon the size of the seat hump, buzzer Although a 140 Ah truck battery would be rather extreme a lead acid battery of 5 - 7 Ah should be easily enclosed.

Cheers Geoff

[jabcb]

If you are going to use an AGM or maintenance free battery, then you also need to upgrade to a modern rectifier/regulator.

[buzzer]

It would depend upon the size of the seat hump, buzzer Although a 140 Ah truck battery would be rather extreme a lead acid battery of 5 - 7 Ah should be easily enclosed.

Cheers Geoff

As small a hump that I can get away with Geoff

[buzzer]

If you are going to use an AGM or maintenance free battery, then you also need to upgrade to a modern rectifier/regulator.

Thanks, that's Interesting, not thought about that... I would like to use a small maintenance free battery, do you have any links or information on what I need to upgrade the rectifier?

I will be making my own loom, so any other upgrades can be catered for while doing this, happy for any suggestions.

The bike has not run for 30 years, so I am not sure about the ignition side of things yet...

[rngdng]

On both my TS400 and my GT750, I have successfully used sealed batteries. My GT has a 2AH battery from something .... I bought it for it's size. Since I don't use the electric starter, it's fine. I've had no charging problems. On the TS400, I used the early 12v electrics, with a GT750 rectifier, and a GT500 regulator. I don't remember how I wired it, but it worked fine.




Lane

[Zunspec4]

If you are going to use an AGM or maintenance free battery, then you also need to upgrade to a modern rectifier/regulator.

What is the reason for that, jabcb? I Fitted an AGM to my Seeley Honda 750 which still has the original reg./rect. and wouldn't want to mess it up.

Cheers Geoff

[ConnerVT]

Can't speak for the Honda electrics, but the Suzuki charging systems up through the 1970's tend to generate a higher voltage than a sealed AGM (glass mat) battery can tolerate. In fact, in the smaller displacement Suzuki, they would omit the voltage regulator completely, and use the battery to regulate the voltage.

A lead acid wet battery is much more forgiving of high voltages. It will generally just "boil" the electrolyte, which you would regularly need to refill. And stain your chrome.

A glass mat, maintenance free battery, when exposed to high voltages, will also boil of the electrolyte, drying out the mats, which you can not refill.

[Zunspec4]

Thanks Connor,

I'd better check the voltage output on the Honda to be on the safe side.

Cheers Geoff

[Craig380]

When charging a sealed battery off the bike, you're not supposed to exceed 14.1V because above that voltage, the electrolyte starts to give off gas which it cannot vent ... so I think around max 14 across the terminals at 4,000rpm is the max you should have

[ConnerVT]

Voltage is correct. But AGM do have a vent. But they contain less fluid (by volume) than traditional lead-acid batteries. The issue is that the electrolyte cannot be added to AGM batteries, which will find its way out the vent as gas and vapor.

[titan performance]

You could do away with the battery altogether? Fit a battery eliminator, and use whatever seat unit you like....

[jabcb]

The T500/GT500 use a pretty lame voltage regulator. It is considered normal for voltage to get up to around 16V. That is too much for an AGM battery.

I use a Tympanium rectifier/regulator on my T500.
Its popular with the vintage Triumph guys & costs around $50.
Not sure what alternatives are readily available in the UK.

The GT750 has a car-style alternator. Properly adjusted it can control voltage much better.
Oregon motorcycle parts has modern upgrades for the GT750 rectifier & regulator.

AGM battery manufacturers generally recommend max voltage around 14.7V. (Does vary a bit.)

[jabcb]

The GT500 has PEI — the ignition is completely separate from the alternator/battery circuit.
The GT500 will run just fine without the battery.

The T250/T350/GT250/T500 have permanent magnet alternators — some of these bikes will start & run OK without a battery.

Running these bikes without the battery is a big NO-NO.
They use the battery to control voltage.

A few years ago I checked the timing on the T350 in my avatar pic.
Got interrupted.
When I got back to it, I started the bike with a disconnected battery.
Started & ran fine but it blew out all the lights except for the turn signals!!!