12 volt conversion -heat failure?

[hamiltia]

Bike failed on recent run in very hot weather
Boyer Bransden Powerbox single phase fitted
Ammeter showed strong/full discharge current at time of failure
Engine continued to run (battery?) but wouldnt accelerate
Breaking & making battery connection temporarily fixed it & bike ran a few mins then failed again.

Seems to me it must be the Box-and that damage is likely to be permanent?-will test this weekend- but any tests /suggestions would be welcome.

[CR]

You don't say what model?

If the Powerbox fails the residual charge in the battery (if the battery is okay) should last for miles and miles of daylight running and shouldn't affect the performance of the engine in any way (I'm assuming coil ignition).

Heavy current discharge could indicate failing coil (internal shorting). Modern coils need good heatsinks and fail almost instantly when they go. Older coils will often fail under high temperatures and produce an intermittent and weak spark. Innability to accelerate the engine indicates that the spark may be weak.

Check the coil!

[lawrence]

Do you have electronic ignition?

I had a similar problem with my Boyer EI and tried replacing everything including coils with only temporary successes. Eventually I fitted a relay switch direct from the battery and it has since been as good as gold. Somewhere there must be an intermittent poor connection in my loom.

[hamiltia]

Thank you both
Model is G3LS
Ignition is by points & coil
All parts for 12V conversion were from Al Osborne electrics ie coil and PowerBox
Boyer PowerBox is to rectify the AC from alternator (and raise to 12V I presume)?
Will check coil-current thru it from charged battery looks normal by the bikes ammeter though...but then its cold again..

ian

[CR]

The Boyer Powerbox has three functions. Firstly it rectifies the AC output from the alternator to DC for the battery. Secondly, it regulates the battery charge (without the need for complicated lighting switch wiring and/or Zener diodes). Thirdly, it contains a hefty capacitor which, when charged by two or three kicks on the kickstarter, can provide sufficient output to power a coil ignition system (without the battery connected). It's all solid state and typically very reliable. Whilst it doesn't produce a great deal of heat, it does produce some - and the maker's recommendation is that it be sited in an area with a reasonable degree of air circulation / air stream. I don't know whether these devices have thermal shutdown circuitry, but I've used at least a dozen over the years and never had a failure - or a thermal shutdown.

I have however, had three out of 12 coils fail over the same period. As I stated earlier, modern coils (iron core with encapsulated coils) need good heatsinking and clear airstream. They will overheat quite easily if they're not adequately cooled.

If the Powerbox is running okay when you start the bike, i.e. a good charge is showing on the ammeter - it's working.

[hamiltia]

Thanks CR for your very clear reply.Will let you know how I get on
ian