Electrifying decisions!

Having established that Calbourne was going to need a substantial 230V supply, the question was how to produce it.

The backbone of the system is to be twelve 670Ah 2V traction cells wired in series to give 24V. The reason for going for 24V is to halve the current going to the invertor. Because the inverter will be rated at 5KW, it will draw around 250 Amps. At 12V, this would be a prohibitive 500 Amps.
The inverter/charger will be a Victron Multiplus 24/5000. When a mains supply is connected, it will charge the batteries at 120A @24V.

Victron Multiplus Charger/Inverter

My initial thoughts were to run a Travel Power (or similar) 230V AC engine-driven generator. This would produce 3KW, or 5KW in the case of the Whisper Power. The output could then drive the inverter/charger to recharge the batteries and provide 230V power. Sounds good.

However, problems started to arise when researching the speed these things need to rotate at. They need to go round very fast to produce their rated output. Gardner diesels rotate very slowly - they tick over at around 400rpm. So this would mean a pulley ratio of about 10:1, or 500mm to 50mm. But the real problem is, if you ever did rev the engine to 1200rpm, you would destroy the alternator.

Hmm, back to the drawing board.

Over the next few weeks, I became very familar with Alternator Output Curves! Having settled on a 24V battery system, my aim was to find an alternator which would match the engine performance, by producing a useful output at all rev ranges, without either overloading the engine, or having to run it excessively quickly to produce a good amperage. Then it was a question of establishing the right pulley ratio to make it all happen.

I'm happy to report that I've sourced a Prestolite alternator capable of 155A output at 28V. Coupled with a 3:1 pulley arrangement, this will produce a charge of 50A at tickover (3x420=1250), rising to 120A at cruising speed (3x730=2200).

 The alternator is a hefty lump, weighing in at 30Kg, so it's going to need some beefy bracketry on the engine!


The batteries will be equipped with an automatic watering system and a forced ventilation system which will operate when charging is taking place. The alternator will be fitted with an advanced regulator to provide 4-stage optimal charging. The 24V starter battery will be charged via a 24V to 24V charger.

When the engine is not running, mains power will be produced by a 'silent' Hyundai diesel generator. This is rated at 5KW and uses around 1 litre of diesel per hour. It will be located in the Potter's locker. I've heard from existing users that, while these genny's are very good, they are far from 'silent'. as billed. So I'm planning on lining out the steel locker with thick sound insulation material and feeding the exhaust through an additional silencer. Hopefully this will get the noise down to acceptable levels.