Alternator Cooling Devices

[sunchaser]

Definitely the first part, and the second part too if you need more.


This is the approach (the first part) we are taking on our Nordhavn 68 build. We have dual 200A, 24V alternators on the main engine, which is 10kw of power. A may use that briefly from time to time, but my real hope is to get less power with much less heat output. Stator heating, which is the largest source of heat in an alternator, increases as the square of the current output. So cut output in half, and you cut heating to one quarter.

Peter
Would a PTO driven commercially rated generator be worth considering rather than utilizing a belt driven alternator operating at the limits? Many different types are available for tractors and off road equipment.

Some years ago I saw an approximate 8kw hydraulic driven unit (Winco maybe?) on a Selene.

 

[twistedtree]

Peter

Would a PTO driven commercially rated generator be worth considering rather than utilizing a belt driven alternator operating at the limits? Many different types are available for tractors and off road equipment.



Some years ago I saw an approximate 8kw hydraulic driven unit (Winco maybe?) on a Selene.

Lots of earlier Nordhavns had hydraulic driven alternators for underway power off the main. Most seem to have been abandoned and or removed due to heat generation and poor reliability.

I did search around a bunch for a PTO driven alternator, mostly because I thought there must be a lot of power loss in the drive belt.

I subsequently learned that drive belts are remarkably efficient, especially multi rib serpentine belts which is what my engine has. So that disappeared as a driving factor.

I also found that to step up the PTO speed to one more suitable for an alternator necessitated a gear box, which significantly complicates things and drives up cost. I didn’t want a one-off or odd ball alternator system, so stuck with dual belt driven Leece Neville/prestolite that are more or less off the shelf.

I remain convinced that at least in terms of efficiency, when your alternator load gets to about 30-50% of your smallest generator’s capacity, you are better off running the generator. Not some people keep running off alternators even if less efficient because they don’t want to rack up the hours on the gen and be changing oil and filters all the time, and that’s a perfectly valid trade off. It just matters what you are trying to optimize.

 

[DDW]

The 28Si that I am using is spec'd at 120 deg C "continuous" output. That has to be internal or frame temp as 120 ambient would be absurd. However where that is measured is left "as an exercise for the owner". That is why I've not set the limit to 120 deg C.

On my sailboat, I have a PTO driven Electrodyne with 7KW output. It turns at crankshaft speed (no gearbox, just a driveshaft directly from the damper pulley) and according specs uses 16 hp at full load. This is a different design than an automotive one, the rotor has no coils and is simply a slotted steel disk. It will achieve about 80% output at 1700 rpm and full output by 2000 (280A @ 24V), and will do this continuously. The rectifiers are mounted on the side of the case, not inside. The downside of it is that it is heavy (110 lbs) and makes a whining noise when loaded.

Micro V belts are more efficient, but with lots of power running through them they do wear, as indicated by the dust. I'd prefer the driveshaft for that reason.

 

[FF]

"Having a fan push cool air into a hose from outside the engine room with the hoses other end placed very close to the alternator so the alternators fan can pull said cool air through the alternator, is the plan."


Pumping air out of the engine space is great, pumping air into the engine space can be dangerous as a leaky exhaust can fill the boat with CO2.


A DN 50 alt can be had with built in oil cooling. Available rebuilt at bus parts store.

 

[twistedtree]

The 28Si that I am using is spec'd at 120 deg C "continuous" output. That has to be internal or frame temp as 120 ambient would be absurd. However where that is measured is left "as an exercise for the owner". That is why I've not set the limit to 120 deg C.

On my sailboat, I have a PTO driven Electrodyne with 7KW output. It turns at crankshaft speed (no gearbox, just a driveshaft directly from the damper pulley) and according specs uses 16 hp at full load. This is a different design than an automotive one, the rotor has no coils and is simply a slotted steel disk. It will achieve about 80% output at 1700 rpm and full output by 2000 (280A @ 24V), and will do this continuously. The rectifiers are mounted on the side of the case, not inside. The downside of it is that it is heavy (110 lbs) and makes a whining noise when loaded.

Micro V belts are more efficient, but with lots of power running through them they do wear, as indicated by the dust. I'd prefer the driveshaft for that reason.

Interesting setup on the sail boat. Got any pictures of it?

I’m not sure what 120C continuous output means.

It would make sense if they are saying that with ambient of 120C or less you can run at continuous output. But you feel 120C ambient is very high, and it is. But probably not out of line with the temp under the hood of an automobile, so maybe not so unreasonable.

And what is “continuous output”? If taken literally, it just means some continuous output, but says nothing about how much output.

So maybe they are saying you can run it at a continuous output such that the temp measured at some unspecified location does not exceed 120C. That’s probably the most believable, but where are we measuring the temp?

It’s all vague enough that I really have no idea how I can use this alternator, and under what conditions.

 

[DDW]

First of all, I've mentioned two alternators: a Delco 28Si I'm using on the trawler and an Electrodyne I'm using on the sailboat. Delco says of the 28si: "125 dec C temperature rating". (I said 120 above but reviewing it again it is 125). They do not elucidate beyond that, but it cannot mean 125 dec C ambient, or if it does it comes no where near that. Based on case measurements, 125 deg C measured somewhere on the alternator is pausible. It is an ordinary medium framed J180 mount.

The Electrodyne on the sailboat is an entirely different animal. It is MUCH larger than the Delco and an entirely different design. There are no brushes, no slip rings, and no coils of any kind on the rotor. Their literature suggests routine maintenance of repacking the bearings every 20,000 hours operation. Up to about 1400 rpm it is a net current sink, break even there, and then rapidly building to full output. The rectifier pack is external to the frame but mounted on it. It is being controlled by a Balmar 624 and I've never seen it cut back due to temp (but have taken no temp measurements). The temp sensor is on the rectifier pack. I've seen it produce 300 A for awhile, but my battery (440 AH @ 24V Lifeline AGM) cannot absorb that for very long. I seems to be able to do 250 - 280 A continuously, this happens sometimes charging the battery while running the watermaker and freezing the refer plates simultaneously.

Here is the installation. This is the original driveshaft I built, with a Spicer coupling on one end. That proved to be problematic and failed one day (actually it loosened on the alternator shaft and there was no way to tighten it) so I replaced that with another rubber coupling. That absorbs any misalignment and also the torsional vibration from the 4 cylinder (Volvo D2-75).

Here is the modified driveshaft, rubber at both ends (Vetus BulFlex prop shaft couplings). These have clamp type shaft couplings eliminating any play:

Installed. The SS ring around the shaft is intended to act as sort of a NASCAR drive shaft catcher - if the alternator end fails and comes loose, I didn't want it beating a hole in the hull before I could get it shut down.

Here is the whole installation. Notice the size of the alternator compared to the 2L 75HP engine: