140 amp alternater but only 5 amps !

[coventrylad]

I know im thick, but can some one please explain to me why my 24 volt 140 amp engine driven alternater is only putting 5 amps in to my domestic battery bank (dc clamp meter) now if I switch on my henry hoover which is run through my stirling 24 volt 2800watt combi it rises to 50 amps. Even if the battery bank is quite low on volts i.e 24 volts it still only gives out 5/6 amps to the batterys. I have geared the pulleys to give 2500 rpm alterneter speed at 650 rpm crank shaft speed. It almost seems as the batterys are not "asking for a higher amperage. I only have at the moment two 100 amp batterys conected to give 24 volts. very old batterys as well. so what is happening please ?

[Tony Brooks]

I know im thick, but can some one please explain to me why my 24 volt 140 amp engine driven alternater is only putting 5 amps in to my domestic battery bank (dc clamp meter) now if I switch on my henry hoover which is run through my stirling 24 volt 2800watt combi it rises to 50 amps. Even if the battery bank is quite low on volts i.e 24 volts it still only gives out 5/6 amps to the batterys. I have geared the pulleys to give 2500 rpm alterneter speed at 650 rpm crank shaft speed. It almost seems as the batterys are not "asking for a higher amperage. I only have at the moment two 100 amp batterys conected to give 24 volts. very old batterys as well. so what is happening please ?

 

 

Very badly sulphated batteries that now have a minimal capacity so they fully charge very fast so fully charged withing a short time. Or a high resistance in a battery, connection or cables. Those would be my guesses.

[by'eck]

Following on from Tony's suggestions, put a digital voltmeter across the alternator output (B+ terminal and B- or casing). If you see around say 28.8 volts it may simply be the batteries not demanding any more current because they are fully charged, but more likely as Tony suggests.

 

Then check again at the alternator with a substantial load on the batteries. If the voltage drops below say 26 volts you should see a substantial rise in the current going to the batteries.

 

As well as Tony's suggestions it may be a faulty alternator (blown diode or regulator) but testing as suggested then comparing to voltage at batteries (which ideally should be the same) will show up the problem.

 

BTW a 24 volt 140 amp alternator would be massive - are you sure its that big? In any case with only 100 Ah battery load onto such an alternator, the batteries will be overwhelmed with the incredibly high charge current ratio. This in itself may explain the symptoms.

Edited March 24, 2013 by by'eck

[Biggles]

2500 seems a little slow. Do you have a charge profile for that alternator?

[pistnbroke]

140 A is only the maximum output into a resistive load. When charging a discharged battery you will get a max of 25 A per 100AH of capacity and that will fall very fast as the batteries come up.

 

If it did charge at 140 A your batteries would get very hot as you have 3360 Watts available!!!

[Detling]

"As well as Tony's suggestions it may be a faulty alternator (blown diode or regulator) but testing as suggested then comparing to voltage at batteries (which ideally should be the same) will show up the problem."

 

I had a similar problem with a 110 Amp 12V alternator only providing about 10A at 4000 RPM (cruising speed), it had a 'dead winding' and so was not putting out much, Fitted a new one all hunky dory now but it was a puzzle. A clue was after fast running above 6000 rpm for a 5 minutes it got very hot, too hot to touch and it didn't add much to the battery either.

[coventrylad]

2500 seems a little slow. Do you have a charge profile for that alternator?

Hi ,with the Lister running at 650rpm the alternator is spinning at 2500rpm, at this rpm the avaible amps according to the charge profile is 100 amps, rising to 140 amps at 6000 rpm. I machined two pulleys one for the crank and one for the alternator

[coventrylad]

Following on from Tony's suggestions, put a digital voltmeter across the alternator output (B+ terminal and B- or casing). If you see around say 28.8 volts it may simply be the batteries not demanding any more current because they are fully charged, but more likely as Tony suggests.

 

Then check again at the alternator with a substantial load on the batteries. If the voltage drops below say 26 volts you should see a substantial rise in the current going to the batteries.

 

As well as Tony's suggestions it may be a faulty alternator (blown diode or regulator) but testing as suggested then comparing to voltage at batteries (which ideally should be the same) will show up the problem.

 

BTW a 24 volt 140 amp alternator would be massive - are you sure its that big? In any case with only 100 Ah battery load onto such an alternator, the batteries will be overwhelmed with the incredibly high charge current ratio. This in itself may explain the symptoms.

Yes it is 24 volt 140 amp. Prestolite BLP3250HMP. bought it brand fine new for not a lot of money off ebay and yes its about the size of a small dustbin!were fitted to routeman busses I beleive.as I said when I load the inverter the lister starts to work deffinate change in engine sound, and the amps rise to 50 amp, normally giving just over 28volts wheather on tick over or with a few revs. I must confess i have not checked the volts when under load, will do that friday. thanks for all your help.