12v petrol genny

[Alan Saunders]

...

An ammeter can be in the positive supply to the battery but has to be able to cope with the maximum ampere charge or discharge.

 

or

 

The ammeter can be of the shunt type, the shunt goes in the positive supply and (small) cables/wires are taken from the each end of the shunt to the meter.

 

The full amperage goes through the shunt but not the meter in this case

Do not use an old-fashioned, in-line automotive ammeter; it could, unlike the shunt type result in a half volt drop.

[Neil Smith]

I think I will fit a volt metre, so is it a small wire from D+ and case of alt for earth, I can check amps at various throttle settings with my clamp metre that does DC amps.

 

Neil.

[onionbargee]

Are you aware that if you start the geny from cold connected to flat batteries that will draw high amps from the alternator the engine will stall ?

[Neil Smith]

Are you aware that if you start the geny from cold connected to flat batteries that will draw high amps from the alternator the engine will stall ?

 

Surely that depends on the gear ratio of the pulleys and the engine power vs alternator amps.

 

Neil

[Alan Saunders]

Are you aware that if you start the geny from cold connected to flat batteries that will draw high amps from the alternator the engine will stall ?

So, try again and warm the engine for a minute before applying the load.

[Neil Smith]

Good point Alan, and if it still stalls then I could lower gearing or start main engine for a while to put a bit more charge in, but that kinda defeats the object a bit so will try and get it to charge nearly flat batteries by gearing down if needed.

 

Neil.

[MarkHez]

My 5.5hp Honda engine is mated to a 75 amp alternator, pulley ratio is only about 1.8:1 (not actually measured them, just used what I had), it generates 30amps at idle, stalls out with a 50amp load at revs less than 1200 or so, and outputs 75amp at 2k revs and above. - my limiting factor seems to be engine power at low revs, now that the alternator can't output higher amperages at the RPMS it spins at.

 

Edited February 17, 2015 by MarkHez

[Neil Smith]

What size are your pulleys Mark, and is that 2000 engine revs or alternator revs as if engine revs at 1.8 ratio that's 3600 so probably about right for max alternator power.

 

Neil.

[MarkHez]

Hi Neil, Really haven't measured, thinking about it properly its probably 3" on engine 2" on alternator, so 1.5:1 ratio. I have to run quite a high tension on the belt to stop it slipping under high load, bigger pulleys would slip less.

 

Mark

[onionbargee]

Great engines those G40's, 10 000 hours plus before overhaul have been recorded on some of them.