Two alternators controlled by single Wakespeed regulator

[silvercreek]

Is it possible to control two different alternators, one P-type and one N-type, by a single Wakespeed WS500? (Alternators are otherwise identical Mitsubishi 115A units.)

I "believe" it shouldn't be an issue, because the only wire coming out of the Wakespeed that's shared between both alternators would be the Field Drive output, which I would split to go to each alternator, and P/N-type shouldn't matter for that.

Right???

[sailingharry]

I'm probably going to demonstrate my ignorance, or at least my misunderstanding.

I believe that in a p-type alternator, the negative end of the field wire is grounded and the regulator provides (variable) positive voltage to the other end.

I believe that in an n-type alternator, one end of the field is at permanently 12 volts, and the regulator provides a (variable) connection to ground.

In both cases, it is the field wire. But the behavior of that wire is entirely different.

[HeywoodJ]

While we talk of them as voltage regulators, an alternator regulator's control mechanism is the field current. You can estimate the maximum field current by knowing the maximum regulated voltage and the winding resistance. Typical automotive 12V alternators have field windings of around 2.4Ω, which leads to a full field current of 6A at 14.4V. Bigger alternators may have lower winding resistances and higher maximum field current. A regulator will supply the full field current until the voltage reaches the setpoint (or other fancy regulating points such as temperature, belt load, etc.), then start regulating the field current flow.

The WS500 can support multiple alternators, according to an FAQ:

The WS500 can provide up to 30 Amps of field current output compared to others that only support 15 Amps. 30 Amps allows one regulator to control multiple alternators or specialized alternators requiring very high fields.

But the P/N is going to kill the idea because they do take different wiring at the regulator because the references are different:

The WS500 can be used with different polarity alternators by selecting the appropriate N-Type or P-Type regulator wiring harness.

Think of it this way, in the P regulator the current is flowing from the positive on the battery, through the regulator to the field winding and then to negative. On the N it is the opposite, the current is flowing from the positive at the battery through the field winding, and then through the regulator to negative.

[smac999]

No. The wakespeed harness is different for p and n Alts. One needs neg field voltage abd one needs pos field voltage.

The Alts would be easy to change.

If both were the same maybe. You’d have to see it’s max feild current output. And only if both ants were on sand engine.

[silvercreek]

Thanks all for the detailed replies. This helps clear up my own ignorance and sadly, I think I may have to convert my P-type back to N-type (the factory configuration) if I want to control both from the Wakespeed. Plus a bonus: it will stop the Volvo Penta from throwing intermittent alarms, which is probably worth more to me than the second alternator.

Anyone know how I could modify a Wakespeed P-type harness to N-type? Would save me completely clipping and re-attaching all the wires just to swap harnesses.

[danno7]

One item not considered is the Wakespeed monitors the alternator temperature. It limits field current if the alternator gets too hot. When using one Wakespeed on 2 alternators, you can only monitor the temp of one alternator.

There is another item of engine speed. The Wakespeed monitors the engine RPM to allow higher field at higher RPM.

YOu can probably get by with using the Wakespeed to control the alternator and run the field wire to the second alternator, but this creates a few complications with more unknown conditions.

I have studied this because I have 2 engines also needing Wakespeeds. I have decided to keep it simple and install one Wakespeed on each engine.

[sailingharry]

Originally Posted by danno7

One item not considered is the Wakespeed monitors the alternator temperature. It limits field current if the alternator gets too hot. When using one Wakespeed on 2 alternators, you can only monitor the temp of one alternator.

There is another item of engine speed. The Wakespeed monitors the engine RPM to allow higher field at higher RPM.

YOu can probably get by with using the Wakespeed to control the alternator and run the field wire to the second alternator, but this creates a few complications with more unknown conditions.

I have studied this because I have 2 engines also needing Wakespeeds. I have decided to keep it simple and install one Wakespeed on each engine.

Before I inherited a second Balmar, I ran two alternators on a single Balmar. They were nearly identical alternators on a single engine, so it was reasonable to assume that they had similar temperatures. After about 500 hours of often full load (backed off on temp, of course), I sent both in for a factory refresh. The factory replaced the bearings and brushes, cleaned them up, and said "whatever you're doing, keep doing it."


Higher field at higher RPM is counter productive. Propeller load at speeds less than WOT are way lower than the available engine power (look at the power curves of a propeller overlaid against available engine power at a give RPM -- the engine is WAY more powerful than needed). At full load (within say 10% of red line), that's when the field should be dialed back. Below that 90% of WOT, the engine has huge amounts of excess power. Field should be full (with temperature monitoring) for anything below WOT. My alternators are good for about 15hp load on my 55hp engine, and I have no problem spinning up to 80% throttle.

[CaptainRivet]

Originally Posted by silvercreek

Thanks all for the detailed replies. This helps clear up my own ignorance and sadly, I think I may have to convert my P-type back to N-type (the factory configuration) if I want to control both from the Wakespeed. Plus a bonus: it will stop the Volvo Penta from throwing intermittent alarms, which is probably worth more to me than the second alternator.

Anyone know how I could modify a Wakespeed P-type harness to N-type? Would save me completely clipping and re-attaching all the wires just to swap harnesses.

Which Volvo do you have and which alternators do you have. Why did modify it to n-type?

On the newer volvo with the "lovely" D+ the absolute best solution is to keep the 115A mitsubishi and add a 2nd one also a 115A mitzi, refurbished they are 200bucks. Then use one Nordkyn VSR200. Like this you get 2x85A=170A charge, no modification of the alternators and no issue with D+ or belt slipage.
And cheap...the only thing thats not cheap is the pharmacy volvo price for 2nd alternator mounting kit and i didn't find any reasonable priced aftermarket kit.
I will next year change gearing ratios so to squeeze another 15A of the mitzis...if that works whichbshould due to data sheets (its orange line is 16000rpm and on volvo it does max 6500) its 200A per engine with small investments. Yes i am running them at 98% of their limits which shorts lifespan but for 200Euro per alt i have 2 spares on board. If one survives 5 years i am happy but they should more...on Mitsubishi Canter equipped with cooling truck setup they deliver 100A when truck is in standstill for longer time eg unloading also in hot afrika and survive that more then 10 years. Thats similar environment then my engine room. Their internal temp management is quite good and conservative.

[witzgall]

Chris from Balmar here. Concerning the N vs P type regulation, I have a customer story told to me last week. A service guy from Austria visited the Balmar booth last week at METS in Amsterdam. He told me of a high quality lithium system installed, where alternator shorted internally, but was still outputting power. It was an N-Type alternator. When this happens, the alternator goes full field. THe alternaor is trying to put out as much power as it can, with no voltage regulation at all. The contactor on the battery opened, disconnecting the battery. The external regulator was messaged to turn off the field which it did, but in this scenario, the alternator is still putting out everything it can as the regulator has effectively lost control of the alternator, and the voltage rose over 50V. The batteries were protected, but over 25K of damage to other systems resulted, not to mention the potential fire that could (But luckily did not) happen.

To be clear this is not a common occurrence, but it is the reason Balmar decided to regulate on the P side some 40 years ago, and continue to do this today. If the above would happen to a P-type alternator, the power fuse to the regulator would blow, and the alternator would stop trying to generate power.

Chris