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Old 18-03-2016, 07:54   #16
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Re: Alternator cooling

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Originally Posted by wsmurdoch View Post
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.
There is no lagging on the exhaust system. The runners from the block to the cooled portion of the exhaust are fairly short making lagging not really practical. I will have another look at it later today to see if there is something that could be done. I run my engine with a 190F thermostat I think so I am not too surprised at that temperature.
Blowing out the alternator seems like a great idea - I will do that. It has about 150 hrs on it so it could probably use it.
When I did my test run yesterday I was running at just under 2000 rpm so well above idle when I ran into the cooling issue. I gather that running at idle is about the hardest for the alternator with reduced cooling and high field current.
Thanks!
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Old 18-03-2016, 08:06   #17
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Re: Alternator cooling

Why a 190 thermostat? These things are designed with a 165 or so in mind.
I have wondered myself why so low, too cool isn't good, too cool leads to varnishing the cylinders etc, you actually on a terrestial engine want 190, 195 or so , engine life is longer, I have wondered why so low on marine engines.
I understand why on raw water cooled, but not why on fresh water cooled.

But a battery monitor shows amps in?

See I have a theory that the majority of alternators don't output what their owners think they do, but significantly less, but since they don't actually measure output, many don't really know.
I installed a shunt and ammeter inline with mine after noticing that my 140 amp alternator didn't seem to charge my bank as fast as my 125 amp charger, and I thought it should charge it slightly faster
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Old 18-03-2016, 08:56   #18
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Re: Alternator cooling

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Why a 190 thermostat? These things are designed with a 165 or so in mind.
I have wondered myself why so low, too cool isn't good, too cool leads to varnishing the cylinders etc, you actually on a terrestial engine want 190, 195 or so , engine life is longer, I have wondered why so low on marine engines.
I understand why on raw water cooled, but not why on fresh water cooled.

But a battery monitor shows amps in?

See I have a theory that the majority of alternators don't output what their owners think they do, but significantly less, but since they don't actually measure output, many don't really know.
I installed a shunt and ammeter inline with mine after noticing that my 140 amp alternator didn't seem to charge my bank as fast as my 125 amp charger, and I thought it should charge it slightly faster
I disagree on the engine temperature - I firmly believe that you get better life out of a 190F circulation system than a 180/185 system which is what most car diesels run at. Having said that, I am not sure 5 degrees make THAT much of a difference.
Ah, never mind, you seem to agree with my 190 thinking
The battery monitor shows amps in/out, SOC, volts, time left at current rate of consumption and in my case the monitor on the lithium bank has a relay that activates at a certain SOC % to turn off charging to the lithium bank. Sure they are not totally accurate but it gives you a battery condition at a glance.
On the output, you are correct. The rated output is under certain conditions seen only at startup which is why I am aiming for 160 amps on a 200 amp alternator.

I have done the 'lid off' test and at 2000 engine rpm (although my rpm indicator is flaky at best) I got 160 total amps into the batteries (plus/minus) with a stable alternator temperature of 82C. When I slid the box into place leaving a roughly 2" slot between the case and the bulkhead the temperature shot up too quickly to get meaningful temperatures. The slot was maybe a foot behind the alternator so the alternator was cooled with stagnant rather than fresh air at that point. The sound level with an open box was pretty impressive
I stuck my hand behind the alternator expecting a small hurricane with the cooling air from two built in fans ... what a laugh You might have an issue lighting a cigarette behind the alternator but it wasn't even what I would consider 'windy'! I wonder if I can somehow mount a fan blade on the alternator shaft .....
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Old 18-03-2016, 09:01   #19
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Re: Alternator cooling

Well, this thread came at a perfect time as i'm pondering the same thing. I've got an inline fan but the cheap flex venting has fallen apart. I have two bronze vents on the stern deck but am unsure how to setup the new flex venting to push / pull air from them without sucking in seawater when we're rockin' and rollin. I need to cool my batteries, alternator and battery charger / invertor.
It's a 1982 36' Cape Dory.
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Old 18-03-2016, 09:03   #20
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Re: Alternator cooling

I would
1. go back to a factory thermostat, Yanmar aren't idiots, while I do not understand their reasoning, there must be one.
2. fit a blower to blow air into the front side of the alternator, most common, most easily replaced and maybe cheapest blower is a standard bilge blower, I intend to put the suction hose down in the bilge so it draws cool air out of the bilge to blow over the alternator as opposed to heated air in the engine compartment. I've not done it yet as I have lots of other projects ahead of it.
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Old 18-03-2016, 09:09   #21
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Re: Alternator cooling

My Yanmar thermostat is I believe a 165 degree, which of course is 30 degrees lower than the average automotive thermostat at 195.

30 is a lot
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Old 18-03-2016, 09:10   #22
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Re: Alternator cooling

I have a Catalina 36 MK1. I have not installed it yet but I am going to try two fans in a push pull set up. Pulling in air from one of the back scoops into the engine compartment, and pushing it out the other. My old fan is noisy and not very effective. I also will be replacing all of the air duct hoses with newer aluminum flex duct. I will try to get some temperature readings after I get the system installed.
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Old 18-03-2016, 09:36   #23
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Re: Alternator cooling

Are you sure the temp is the problem with the decrease in output? It seems to me your batteries aren't going to take the full amps long anyway....


How about a louvered opening where you suggest.... in the cover in front of the alternator. Then a big engine room extraction fan aft. This would suck the fresh air right across the alternator.... and get that engine room temp down. Close the louvers when not running.

I've often wondered why no manufacturers make a water cooled alternator. But maybe they don't because the temp isn't a problem ?.
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Old 18-03-2016, 09:45   #24
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Re: Alternator cooling

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Originally Posted by Cheechako View Post
Are you sure the temp is the problem with the decrease in output? It seems to me your batteries aren't going to take the full amps long anyway....


How about a louvered opening where you suggest.... in the cover in front of the alternator. Then a big engine room extraction fan aft. This would suck the fresh air right across the alternator.... and get that engine room temp down. Close the louvers when not running.

I've often wondered why no manufacturers make a water cooled alternator. But maybe they don't because the temp isn't a problem ?.
One of my banks is lithium - they will take whatever I can give them
I am thinking of some kind of close-able system for air inlet.
You can in fact get water cooled alternators but they are pretty specialized and priced accordingly
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Old 18-03-2016, 10:27   #25
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Re: Alternator cooling

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One of my banks is lithium - they will take whatever I can give them
I am thinking of some kind of close-able system for air inlet.
You can in fact get water cooled alternators but they are pretty specialized and priced accordingly
Yeah, until you're swimming watching it burn to the waterline!
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Old 18-03-2016, 11:06   #26
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Re: Alternator cooling

What you need to do to maximize alternator cooling is to fit what is called in aviation a blast tube. It is a duct which routes the incoming vent air going into the engine compartment. It routes this cool air onto the alternator. It should be aimed so that the air flows into where the alternator intakes its cooling air (the cooling fan mounted on it is the air outlet). The point is that you can increase cooling air into the engine compartment with only limited improvement on the alternator. A blast tube will concentrate the cooling where you need it.
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Old 18-03-2016, 11:08   #27
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Re: Alternator cooling

Thanks for your reply with the additional information. You appear to have a somewhat unique situation with your lith bank which can take far more current for far longer than those of us with "traditional" FLA wet cell deep cycle battery banks, where the battery bank acceptance reduces current "as time goes by." You, of course, have a different issue than almost ALL of the Catalina 36s that I know (I have many friends with that great boat), as well as our C34s.

The methods employed by most of us with high output alternators has been to use either or both of the Amp (or Belt) Manager or Small Engine Mode of the Balmar regulators.

Of course, this reduces alternator output seemingly just at the time you want and/or need the highest output, right?

It's not a dilemma, it's a reality.

Maine Sail has written extensively about these issues, and we have posted links to more detailed discussions, like these, in the past:

Alternator heat, Regulator Controls, Small Engine Mode

Alternator heat, Regulator Controls, Small Engine Mode

Small Engine Mode - discussion with link to the picture of the toggle switch: Alternator heat, Regulator Controls, Small Engine Mode

Small Engine Mode - the picture of the toggle switch Alternator Output Management with External Regulators [Small Engine Mode]

After I posted last night, I've been thinking about your situation. Rather than cutting any holes in your engine cover, would it be possible to extend the cover around the alternator to provide more air space around it? IIRC, the alternator is on the port side of the engine, on the side where the galley is.

Good luck.

PS - Unless I missed it, what engine do you have?

PPS - You don't need to be a Member of the C36IA to use their forum, just sign up, it's free. That said, I doubt if many of their skippers would be able to help much with your situation, as I don't recall any of the respondents on their forum having your battery types, but ya never know. I'm certain none of our C34 brethren do.
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Old 18-03-2016, 11:19   #28
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Re: Alternator cooling

I'll share some real life experience here.
You can blow all the cooling air you want on that alternator and you won't substantially cool it down. Oh you may get a few degrees but when it comes to LiFePO4 batteries that can gobble up amounts of Amps that the alternator was simply not designed to put out continuously, adding cooling air is just going to be a feel good activity. If you talk to the folks at Balmar that you want to get 180A out of a 200A alternator for a prolonged period of time feeding a LeFePO4 bank and they will most likely tell you to use their temp sensor to scale back the output or risk burning out the alternator.

The base alternator technology is just not designed for anywhere near continuous duty at the max rating and LiFePO4 batteries are making the alternator guys admit and deal with this.
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Old 18-03-2016, 12:55   #29
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Re: Alternator cooling

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The base alternator technology is just not designed for anywhere near continuous duty at the max rating and LiFePO4 batteries are making the alternator guys admit and deal with this.

I had thought, well I'll get me one of those BIG alternators and take my 140 and put in it spares, I wouldn't mine being able to throw 200 amps at my AGM bank as it will take it.

But I came to a conclusion, the BIG 200 amp alternator is the same frame as my 140 amp, near as I can tell the same amount of metal, same cooling fan etc., then logically if it did hit 200 amps, all that would mean is that it will hit it's temp limit just that much sooner than my 140, with the total amount of current if anything being less than what my 140 will do, before it too hits it's temp limit? Net gain being zip?

Whats the logic of spending BIG $$$ buying a 200 amp alternator, then using belt manager, small engine mode or whatever you call it to limit it's output so it doesn't overheat, as opposed to spending lots less $$$ on say a 100 amp alternator and letting it operate at full output?
Does a 200 amp alternator run cooler at 100 amps than the same frame 100 amp alternator making 100 amps?
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Old 18-03-2016, 14:04   #30
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Re: Alternator cooling

Couldn't (2) 100-amp alternators be made to work together, providing redundancy?
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