Alternator Cooling

[sailingharry]

So I have a pair of Powerline alternators on my 4JH2E -- a 120 and a 150. They cheerfully put out a total well over 200A, and will do that for an hour or more. Unfortunately, they are showing heat damage, and I've sent them off for a preemptive rebuild. I want to make them run cooler.


First thing, I'm going to dive into the load management on the external regulators. But really, my problem isn't too much current (I WANT that!), it's too much heat. Reducing load is a reaction, not a solution.


First, we know that "high output small frame alternator" is an oxymoron. But it's a sailboat, and a big frame won't fit. And neither will a cooling system! There is not room anywhere to run ducts from a blower to the alternators.


I just had an idea. My engine room is moderately air tight (although fully connected to the bilge going forward). What if I mount a 250CFM Jabsco blower on the back bulkhead of the engine room, routed up to the deck vent (this would replace the useless little inline RULE in a dryer duct laying in the bilge). Then, mount a 4x12 floor register (like your home heating system) in the companionway stairs? This would put the register about 6" in front of the alternators. The blower would extract hot air from the engine room, and a fair amount of the makeup air would flow through the register, right at the alternators. Sure, the blower draws like 15A, but if it allows my alternators to run at 10% more capacity, I'd be ahead.


Would this actually get results? Or would I draw so much air from all those little engine room leaks that there wouldn't be much effect? Of course, air flow in general wouldn't be a bad thing for ambient temperatures. Are there any safety type hazards I'm missing in this?

[kapnd]

You probably have inadequate air supply to your ER in the first place, so drawing air out would only exacerbate that. (And consume additional power, increasing temps!)
The engine consumes quite a bit of air, look it up in your spec book.
It’s basically engine cylinder displacement x rpm.
Put a thermometer in the ER, operating ambient air temps shouldn’t exceed about 110*.
The added grating minus the blower might improve airflow, and cooling, but it could also make your cabin smell and sound just like the ER!

[sailingharry]

KAPND,


When I first started contemplating this, I was trying to provide fresh air to the alternators via ducted SUPPLY air. And, I was wondering if that would push hot ER air out all those cracks and openings into spaces like the main cabin and the quarterberth and the battery compartment.


But you suspect that I'm actually running at a negative pressure in the ER? So a 250CFM blower pushing air in wouldn't actually have to be "leaked out" someplace?


If indeed I'm running a negative flow right now, the grating wouldn't send engine room smells out, at least not while running. Fortunately, for whatever reason, I don't seem to have any odor in my engine room.



I do worry considerably about cutting holes in the nice sound insulation a PO added. The admiral already says the engine makes too much noise -- and she cooks within about 3 feet of it!

[tkeithlu]

The temperature of the operating alternator is well above the temperature elsewhere in the engine compartment, and the air in the compartment is replaced pretty quickly, given a running engine. Therefore, circulation of the air in the compartment, over the alternators, is a working approach independent of sucking more air into the compartment. So, consider starting with bigger fans on the alternators themselves. That's a common problem for racing cars, so Summit Racing is a good source for add-on alternator fans:

https://www.summitracing.com/search/...iAAEgLfPvD_BwE

[pcmm]

First that is ALOT of alternator(s) for a 4JH2E!!! How are you driving them? Serpentine belts? double V-Belts? Your engine room should already have an exhaust blower. But in this situation I'd be tempted to provide positive air flow over the alternators. You might want 1 blower for each alternator with a duct directly feeding each alternator.

[sailingharry]

Interesting thought you bring up about engine air flow. The 4JH2E is about 120 Cubic Inch. At 3000RPM, that's about 200CFM -- or about what the biggest Jabsco blower can do.


Now what to do with this info? LOL.


Even if the engine room is running at a negative pressure, it is still getting 200CFM of fresh air (or the engine would die). So to reduce temps, I need to get even MORE flow. Blowing air in would only replace air that is already leaking in. To get more air flow, I'd either need to get HUGE amount of air blown in, or extract more (while providing ways for makeup air to enter).


While I say my ER is "somewhat air tight" I'm only saying it is a box. There are lots of holes in it for wires and hoses and what not, as well as some openings forward under the floor boards to the main bilge. Obviously, all those are where air is entering. But it leaves open the question "is that adequate?"

[pcmm]

Originally Posted by sailingharry

Interesting thought you bring up about engine air flow. The 4JH2E is about 120 Cubic Inch. At 3000RPM, that's about 200CFM -- or about what the biggest Jabsco blower can do.


Now what to do with this info? LOL.


Even if the engine room is running at a negative pressure, it is still getting 200CFM of fresh air (or the engine would die). So to reduce temps, I need to get even MORE flow. Blowing air in would only replace air that is already leaking in. To get more air flow, I'd either need to get HUGE amount of air blown in, or extract more (while providing ways for makeup air to enter).


While I say my ER is "somewhat air tight" I'm only saying it is a box. There are lots of holes in it for wires and hoses and what not, as well as some openings forward under the floor boards to the main bilge. Obviously, all those are where air is entering. But it leaves open the question "is that adequate?"

Not sure why you are equating the engine displacement with cooling the alternator?

be aware that you are using 25% of the engines max 44hp to drive the alternators (roughly)

The bigger issue is directing air flow through/over the alternator directly. The engine breathing, while it moves 200cfm is pulling it from the whole compartment generally. you want air forcefully directed to the alternators.

[sailingharry]

Originally Posted by pcmm

Not sure why you are equating the engine displacement with cooling the alternator?

be aware that you are using 25% of the engines max 44hp to drive the alternators (roughly)

The bigger issue is directing air flow through/over the alternator directly. The engine breathing, while it moves 200cfm is pulling it from the whole compartment generally. you want air forcefully directed to the alternators.

The engine displacement discussion came from the post about the engine already extracting a lot of air from the engine room.


You are right that I need to push air at the alternators -- hence, the idea of inserting a vent grate in the companionway stairs right in front of the alternators, so makeup air would be right there.



I have two alternators. The smaller (120A) is in the stock position. While it is more than conventional wisdom recommends for a single belt, I have minimal belt dusting (although I have never seen it give more than 70A -- part of why it is back for rebuild). The bigger 150A is driving by a serpentine belt. It's mounted on the starboard side, and I machined an adapter to mount a multi-v pulley for a Mack Truck on the front. I'm pretty happy. This one will routinely puts out up to 130A or more, depending on the situation.



So, at 250A (let's hope I get that after rebuilds!), that's just under 5HP. Assuming 50% efficiency, that's 10HP -- so close to your 25% number. I consider that a good thing, especially if I'm running it at anchor or in neutral while sailing. Probably a bad thing when needing 100% of engine power -- might be worth considering a switch.


Pic of the install. The bracket was made by a buddy with the same boat -- and when he does ANYTHING he does several, so he had a spare.

[sailingharry]

Originally Posted by tkeithlu

The temperature of the operating alternator is well above the temperature elsewhere in the engine compartment, and the air in the compartment is replaced pretty quickly, given a running engine. Therefore, circulation of the air in the compartment, over the alternators, is a working approach independent of sucking more air into the compartment. So, consider starting with bigger fans on the alternators themselves. That's a common problem for racing cars, so Summit Racing is a good source for add-on alternator fans:

https://www.summitracing.com/search/...iAAEgLfPvD_BwE

Interesting link. The alternators are in Fort Worth getting rebuilt, so I can't dig more right now -- but there's a lot of choices there at Summit. The ponder, of course, is how much are they selling "bling" (polished/clear coated/billet aluminum) and how much are they selling real cooling. But that's always the question.


Has anyone played with high performance fans, and do they work?

[pcmm]

Originally Posted by sailingharry

The engine displacement discussion came from the post about the engine already extracting a lot of air from the engine room.


You are right that I need to push air at the alternators -- hence, the idea of inserting a vent grate in the companionway stairs right in front of the alternators, so makeup air would be right there.



I have two alternators. The smaller (120A) is in the stock position. While it is more than conventional wisdom recommends for a single belt, I have minimal belt dusting (although I have never seen it give more than 70A -- part of why it is back for rebuild). The bigger 150A is driving by a serpentine belt. It's mounted on the starboard side, and I machined an adapter to mount a multi-v pulley for a Mack Truck on the front. I'm pretty happy. This one will routinely puts out up to 130A or more, depending on the situation.



So, at 250A (let's hope I get that after rebuilds!), that's just under 5HP. Assuming 50% efficiency, that's 10HP -- so close to your 25% number. I consider that a good thing, especially if I'm running it at anchor or in neutral while sailing. Probably a bad thing when needing 100% of engine power -- might be worth considering a switch.


Pic of the install. The bracket was made by a buddy with the same boat -- and when he does ANYTHING he does several, so he had a spare.

conventional wisdom is it takes 1hp per 25amps to generate.. but if its working, great! I would stick with forcefully blowing air with engine room blowers. If you have a grate in the front of the engine room, I would duct those grate openings directly to the alternators.

[sailingharry]

Originally Posted by pcmm

conventional wisdom is it takes 1hp per 25amps to generate.. but if its working, great! I would stick with forcefully blowing air with engine room blowers. If you have a grate in the front of the engine room, I would duct those grate openings directly to the alternators.

I'm an engineer, so calculations always work for me (I never memorized the quadratic equation -- it was just as easy to solve it). But it's great when calculating it came up with 10 HP and conventional wisdom came up with.....10HP! LOL.


I'm going to have another boater over later this week. We'll look at that tight engine room and brainstorm ways to duct a blower to the alternators. Not that I'm optimistic (wait... is negativity a good way to start a brainstorming session?)

[hjohnson]

An option that I am currently investigating is moving the rectification off board from the alternator in addition to the regulation. About half the heat in an alternator comes from the diode pack. Moving that out of the alternator and into an actively cooled box seems to be worth the effort. On my boat, it would likely do double duty as a cabin heater, as we do a significant amount of winter sailing.

I’m heading to a local starter and alternator shop to see what they have to say. I need to get both rebuilt anyway.

[goboatingnow]

Removing the diode pack and replacing it with some chunky avalanche diodes mounted on a big heatsink isn’t too onerous a job. You can bring out the field coil connection from the brushes at the same time to facilitate an external regulator

[sailingharry]

Offloading rectification certainly is tempting. Less heat, and probably frees up ventilation through the alternator. I am not sure it's as easy as it sounds though -- although I'm sure it is very "alternator dependent." One would assume that the rectifier leads need to be massive -- total cross sectional area equal to the existing alternator output, as a first approximation.


Of course, the ABYC standards for wire size don't quite meet the OEM standards. Have you ever considered that the entire 150A rated output (that's what, #2 minimum wire size, or .053 in^2?) goes through a steel 5/16 bolt (some are 1/4") that has a cross sectional area of about .05 in^2, but has only 10% the conductivity (10 times the resistance)? On my 150A alternator, that got so hot (perhaps a poor connection, too) that it literally melted the insulation off the end of the 2/0 alternator cable!

[hjohnson]

Originally Posted by sailingharry

Of course, the ABYC standards for wire size don't quite meet the OEM standards. Have you ever considered that the entire 150A rated output (that's what, #2 minimum wire size, or .053 in^2?) goes through a steel 5/16 bolt (some are 1/4") that has a cross sectional area of about .05 in^2, but has only 10% the conductivity (10 times the resistance)? On my 150A alternator, that got so hot (perhaps a poor connection, too) that it literally melted the insulation off the end of the 2/0 alternator cable!

Thankfully I’m not asking my poor little 1GM10 (or future Beta 14/16) to put out 150A… I would like some HP left over for the prop. That said, I’ll be happy if I can get a reliable 70A into my lithium bank. I am a little loathe to spend too much on the alternator for the 1gm10, as I don’t know how much longer that engine will still be put-putting along. The Betas have a serpentine belt, so can actually drive larger alternators.