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Old 17-03-2016, 23:52   #1
Jd1
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Alternator cooling

It has become painfully obvious that I will need to provide more cooling air to the engine compartment in order to achieve better output from my 200 amp Balmer alternator. It would appear that I am maxing out at about 100 amp give or take if I want to keep alternator temperature below 100C.
My boat is a Catalina 36 MKII and the alternator is maybe 4 or so inches from the engine cover that sits under the companionway stairs.
The obvious thing to do is to cut a 5 or 6" hole into the engine cover and stick a fan into the hole to blow cool air onto the alternator.
I am having several concerns with this and wonder how other people have handled the cooling issue. My biggest concerns are noise (with a big hole in the cover), possible smell and above all, implications in case of a fire. There might be other issues that I am not aware of.
I currently have an exhaust fan that sucks some (not very powerful) air out of the engine compartment. I have usually not bothered turning that fan on but have tried it and it does lower temperatures but only a few degrees. I am thinking that this setup would reduce/eliminate my concern of smell, especially if I install a more powerfull (or second) exhaust fan.
Another option I could see is to put a smaller hole into the engine cover (let's say 3") with no fan and completely depend on an improved exhaust fan to pull air through the engine compartment.

What things have you tried and what did eventually work for you? Thoughts ?
BTW, there isn't a lot of room around the front of the engine so things heat up quickly.
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Old 17-03-2016, 23:58   #2
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Re: Alternator cooling

Are you aware of the Catalina 36 International Association? www.c36ia.org

I don't recall hearing of anyone doing or needing to do this. And our boats are very similar, and neither have our skippers found a need to do so.

I'm running a 100A alternator with a Balmar MC612 external regulator to FLA batteries, NOT agms.

What kind of batteries do you have? What kind of regulator?
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Old 18-03-2016, 00:14   #3
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Re: Alternator cooling

Quote:
Originally Posted by Stu Jackson View Post
Are you aware of the Catalina 36 International Association? www.c36ia.org

I don't recall hearing of anyone doing or needing to do this. And our boats are very similar, and neither have our skippers found a need to do so.

I'm running a 100A alternator with a Balmar MC612 external regulator to FLA batteries, NOT agms.

What kind of batteries do you have? What kind of regulator?
Thanks for your reply. Yes I am aware of the Catalina association but am not a member. Yes, your Catalina 34 is probably identical as far as the engine setup is concerned. I run a Balmer 200A alternator with a serpentine pulley setup and an MC612 external regulator. I have a 350 AHr FLA bank and a 700AHr lithium bank. Your FLA batteries, if around the same size as mine, will accept about 60 amps of charge current but quickly drop below that. With that amount of generated power you will have no issues with cooling. I am shooting for 160 amp continuous alternator output (and 200A for the first little bit of time) so about three times what you are generating.
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Old 18-03-2016, 00:23   #4
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Re: Alternator cooling

go for a run with the stair hatch off and see if amps increase?


at least gives you some data. if it doesn't help then a 5" hole probably won't.


can you duct outside air direct to the alt with a fan?
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Old 18-03-2016, 00:34   #5
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Re: Alternator cooling

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Originally Posted by smac999 View Post
go for a run with the stair hatch off and see if amps increase?


at least gives you some data. if it doesn't help then a 5" hole probably won't.


can you duct outside air direct to the alt with a fan?
I am hesitant to do that as the stairs will not be in place to be able to get up and down (the engine cover supports part of the stairs). I can and will however do a trial run while at the dock with that kind of a setup. The alternator has two fans in it and I have no doubt that given lots of air it will output what I am asking of it .... (trial is scheduled for tomorrow)
The alternator is directly behind the cover so yes, if I provide a hole for air it will flow directly over the alternator.
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Old 18-03-2016, 01:09   #6
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Re: Alternator cooling

You might want to have a look at how fast the alternator is running.


Because we put alternators on massive battery banks (lots of amp hours to recharge) they tend to be required to operate at the high end of their ampage output ratings.


We spin the alternators with diesels which we run at comparatively low RPMs most of the time, which means the alternators may be operating towards the low end of their speed ratings. Be mindful that many alternators are designed to run on petrol engines at higher engine revs.


The combination of high, heat creating currents coupled with low alternator RPMs leads to alternator overheating.


You may want to look at changing the pulley ratio on engine/alternator as the amount of cooling air sucked through the alternator depends upon the alternator speed.


Since you have a diesel which is governed to a maximum RPM the pulleys should be sized to spin the alternator at it's maximum RPMs when the engine is at it's maximum governed RPMs.
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Old 18-03-2016, 02:51   #7
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Re: Alternator cooling

While your observations are correct for a standard automotive alternator, my alternator is not an automotive type - at idle it produces about 50-60 % of maximum output power and by the time I hit 2000 rpm it produces maximum output. There are two fans for additional cooling at lower rpm. I wouldn't be surprised if the engine bay reaches 80C during normal operation and there just isn't enough of a temperature differential to cool the alternator. Yes, increasing alternator RPM would help a bit but at a cost of higher fuel consumption because of windage losses and higher wear because of the higher rpm. IMHO, a more efficient setup involves cooling down the ambient temperature in the engine bay.
Oh, I think I would also run into issues at idle speed - higher rpm would mean that I would probably have full alternator output at idle a(yes, I could manually decrease it if I wanted to but why) and I suspect that this would be too much load for the engine when it also has to move the boat.
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Old 18-03-2016, 03:08   #8
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Re: Alternator cooling

Unless you have a hearing aid you can switch off during engine operation I would not cut a hole in the engine cover. Diesels have a lot of advantages but quietness is not one of them.

I would suggest you beef up the extractor fan for your engine compartment. Jabsco has some potent ones (continuous duty), although a bit expense.

Then also install a duct towards the alternator for fresh air. You could make that blower-assisted as well.
Putting 200A out will make any alternator run at quite some temperature irrespective of the engine next to it. So you will need to supply it with cool air to prevent temperature build-up
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Old 18-03-2016, 04:09   #9
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Re: Alternator cooling

Quote:
Originally Posted by Jd1 View Post
... I wouldn't be surprised if the engine bay reaches 80C during normal operation and there just isn't enough of a temperature differential to cool the alternator ...
The maximum temperature of the engine room should never exceed 140 degrees F (60 deg C), within 3/4" of any electrical equipment (Alternator), and should never exceed 115 deg. F (40 deg C) anywhere in the engine compartment.

See Caterpillar’s excellent paper on Engine Room Ventilation:
www.gregorypoole.com/products/electricpowergenerator/Documents/LEBW4971-02 ENGINE ROOM VENTILATION.pdf
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Old 18-03-2016, 05:35   #10
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Re: Alternator cooling

Gordo... link broken and I fussed about with finding and fixing it... and failed

jd1

Push and pull fans... exchanging the air is your solution...
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Old 18-03-2016, 06:25   #11
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Re: Alternator cooling

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Originally Posted by GordMay View Post
The maximum temperature of the engine room should never exceed 140 degrees F (60 deg C), within 3/4" of any electrical equipment (Alternator), and should never exceed 115 deg. F (40 deg C) anywhere in the engine compartment.
Well I am definitively exceeding that! I used some heat sensitive printer labels on some of the wires in the engine compartment and they have turned a 50% black (or so) colour .... definitively over 60C (at times)
I will have to check things out in the morning ..... my mooring line just parted and I had a bit of a panic happening .... I am just reading this while calming down after a rather rude awakening and some drifting .....
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Old 18-03-2016, 06:52   #12
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Re: Alternator cooling

I have the same issue, that is I get full output for a few minutes and then due to alternator temp, the regulator cuts back to float voltage which of course cuts amp output way down.
A very real solution if you can is to increase alternator RPM, you will never notice increased fuel consumption, as there really isn't any. Increasing RPM helps in two ways, first of course the internal cooling fans move more air, but also the alternator doesn't produce as much heat producing the same power at higher RPM than it does at lower RPM.
My plan is to wire in a bilge blower to blow on the alternator, switched to the ign circuit of course, and have it pull air from a 3" hose form the cooler bilge.
I haven't done it yet, but it should help.

I'd run my alt faster if I could figure out how without replacing my very expensive serpentine pulleys
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Old 18-03-2016, 06:55   #13
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Re: Alternator cooling

How do you know what your alternator output is? I ask as most people don't know amperage output, just voltage.
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Old 18-03-2016, 07:34   #14
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Re: Alternator cooling

80 degrees C (176 degrees F) seems really hot for an engine compartment. That is hotter than the engine block should be. My engine water temperature runs around 165 degrees F, and in B.C. you are floating in cooler sea water than I am here in the Bahamas. Do you have something that should be insulated in the engine compartment that is not? Is there proper lagging on the hot parts of your exhaust system?

Once you get the air temperature down to a more reasonable temperature, don't dismiss spinning the alternator faster. The fans move considerably more air and move it faster over the coils and diodes. It does make a difference. Also, at higher alternator speeds less field current is required to produce the same output current. That lowers the amount of heat (IR) generated in the field windings of the rotor.

Additionally, you might try blowing out the alternator with a good shot of compressed air. In my case it blew out bunches of belt dust and made a real difference in the alternator temperature. It is now on my "do it annually" list.
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Old 18-03-2016, 07:45   #15
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Re: Alternator cooling

Quote:
Originally Posted by a64pilot View Post
How do you know what your alternator output is? I ask as most people don't know amperage output, just voltage.
Each battery bank has a battery monitor / SOC meter
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