twin alternator instalation

[Timothy]

I don't know if this is the right forum to ask this question but I will give it a try.I wish to install an additional 200 amp balmar alternator on my Perkins 4-108 . I am already running a 200 amp Balmar on two belts for the house bank and on another belt a 60 amp alternator for my starter battery and the water pump. I have no more space between the center board trunk and the power take off to install any more pulleys on the power take off so I must run the additional 200 amp altenater on the same two belts as the original 200 amp altenater . I think I can do this as long as I maintain sufficient surface area on the altenator pulleys. I have devised a way to do this in the space that I have but it requires that the bets turn around snub idlers with their backs bearing on the pulleys. I do not want to change the pulleys on the power take off or the pulleys on the alternators which are for half inch v belts. Can I use flat pulleys for the idlers (tension but no load ) or do I use all v pulleys and double v belts? Thanks in advance for any ideas.

[Arnot]

You might have a couple of other problems here...
The torque requirement of two 200A alternators is going to be very high at lower speeds and assuming that battery charging is an important priority, you will want to keep the engine speed as low as you can to reduce noise and fuel consumption.

The potential problems are;
1) It is likely that at low to medium engine speed, the torque requirement of the alternators when the batteries are flattish will exceed the engines ability to provide it and you will hit a rev limit until the batteries are more fully charged. The symptom is that the engine does not respond to the spped control apart from making a larger cloud of black smoke.
2) There is a limit to the torque that two "V" belts can transmit and I suspect that you are already near this. If you add another alternator you will probably find that the belts quickly stretch and start to burn.

It might be an idea to see if your present alternator is actually delivering what it should, it may be that there is some inadequacy in the installation that is preventing this. Alternatively you may just have to learn to be patient ;-)

Regards

Arnot

[pistnbroke]

Perhaps you could explain what you hope to gain with the extra alternator ...rated at 200a does not mean it will charge a battery at 200a ...that is the figure it will supply to resistive loads .. lights and similar .. It is only the difference between battery volts and alternator volts that drives the charge current .....You would not want to charge a battery at more than 25A per 100ah of capacity or it will get very hot and gas.
You cannot charge a battery at 25a all the way to fully charged ...the current will taper off fast above 80% charge as the voltage difference nears zero...

Usually a single 1/2 in v belt will handle a 100A alternator so you have another problem there .

Are you using the programmable regulator and battery temperature sensiing ..???