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Alternator Cooling

Mar 20, 2007
500
Catalina 355 Kilmarnock, VA
Hey RC - I am having a problem with my alternator overheating any time my batteries drop below about 90% SOC. I can reduce the temp by going to Small Engine Mode (switch at helm), but that obviates the benefit of the HO alt. My engine space is very compact, especially around the front of the engine. I'm thinking of ducting my engine room blower directly to the alternator - question is, would it be better to blow fresh air in toward the front, or suck air out from behind? Also plan to see if I can rotate the engine air intake horn toward the front of the engine to pull more air through the front of the compartment, though it's on the opposite side from the alt.
My system: Yanmar 3YM30, Electromaxx 140 amp alt with serpentine belt, Balmar 614 (Belt Manager currently at 70%), 2 Lifeline 4D house, 1 Lifeline group 27 start/backup, Blue Sea magnetic latch ACR.
 
Feb 10, 2004
3,522
Hunter 40.5 Warwick, RI
RC will have an answer for you, but FWIW I had the same issue of a hot alternator. I did not have any engine compartment blower so I added a 3" in-line fan and duct and vented it out of an existing flow-thru vent port. My Balmar alternator pulls air from the back to the front so I placed the duct entrance near the front of the alternator and pulled the hot air from the alternator area to the outside. My alternator still goes into the reduced mode, but it is better. If I could figure out how to blow outside cool air into the rear of the alternator along with my hot air exhaust , I think it would be much better.

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Mar 20, 2007
500
Catalina 355 Kilmarnock, VA
Thanks, Rich. The EMaxx pulls air the opposite way, but I suspect it doesn't make much difference.
 
Jun 6, 2006
6,991
currently boatless wishing Harrington Harbor North, MD
So how big is your battery bank? almost all your HO will be from taking your batteries from <50% SOC to 90% SOC. After that you should be in absorption mode (about 25% of HO) and then float (0.05% of HO). so I'm thinking you have a honking big battery bank (like over 1000 AH) OR your regulator is not set up correctly or of the wrong type. A 140 amp alternator should not overheat charging a 90% SOC bank unless it is REALLY big bank (which I doubt is the case here)
You need to check the voltage while charging. Above 90%SOC it should be around 14.6 but the amps out (which is controlled by the battery's internal resistance that goes up markedly when you get to around 90%SOC) should be much lower.
With all that said it does sound like you need to vent the hot air somewhere so the alternator does not over heat when you do have deeply discharged batteries
 
May 7, 2012
985
Hunter e33 Maple Bay, BC
My system: Yanmar 3YM30, Electromaxx 140 amp alt with serpentine belt, Balmar 614 (Belt Manager currently at 70%), 2 Lifeline 4D house, 1 Lifeline group 27 start/backup, Blue Sea magnetic latch ACR.
I had alternator overheating issues when I initially installed my new HO system some 18 months ago. The cause was similar to yours, compact engine room and insufficient air exchange. My solution was to relocate the 4" blower (exhaust) hose to directly above but not touching the alternator, maybe 2" - 3" above the alt body. Because of the compactness of the engine room it was not possible to position the hose at any other location in proximity to the alt. I also remove an engine room side hatch (approx 0.5 sq ft) to allow air ingress if the SOC is <85%. The result has been that the alt temp rarely exceeds 90C (194F) with alt o/p in the order of 80A as measured at the batteries with a Victron BMV600s battery monitor.
For comparison purposes my system: Yanmar #YM30, Balmar 100 amp alt with V-belt, Balmar 614 (Belt Manager currently at b-2 or 90%), 4 US Battery GC (464 AHr), Group 27 (100AHr) Reserve, Echo Charge ACR.
FYI: the AL 1 (alternator temperature) has been reduced from the default value 108C to 104C as per a Maine Sail recommendation.
 
Jan 22, 2008
169
Beneteau 343 Saint Helens, Oregon OR
3YM30, Balmar alt. and MC612. I moved exhaust fan suction up near back of alternator but also found moving the MC-612 out of the engine compartment to help.
 
Feb 6, 1998
11,454
Canadian Sailcraft 36T Casco Bay, ME
Hey RC - I am having a problem with my alternator overheating any time my batteries drop below about 90% SOC.
With a 140A alternator on a 420Ah battery bank, figuring approx 120A when hot, your charge rate is approx .28C or 28% of Ah capacity. With .2C charge rate from 50% SOC, on a Lifeline battery bank, bulk is approx 1:15 minutes long. With a charge rate of .4C bulk is approx 20 minutes long. You are likely 30-35 minutes in bulk from 50% SOC. If you are over heating in the 90% SOC range this is pretty tough to do because you will be in absorption and current will be declining pretty rapidly. My first question would be how are you determining SOC? Under your normal/average house loads you should not be letting your Lifelines dip below 12.2V. This will be approx 50% SOC.

Charge rate affects the bulk/absorption transition point in the SOC curve:

Charging at .4C, from 50% SOC, the transition from bulk to absorption = 63% SOC (approx)

Charging at .2C, from 50% SOC, the transition from bulk to absorption = 77% SOC (approx)

You will be somewhere between theses two points where you hit absorption voltage unless you are de-rated down towards .2C then your bulk to absorption transition will be at approx 77% SOC...


I can reduce the temp by going to Small Engine Mode (switch at helm), but that obviates the benefit of the HO alt.
Small engine mode is a 50% cut in field potential. If your engine room is so tight that you need to go to 50% field then you simply need more air. The E-Maax alt brings air in from the front and back and spits it out the middle. If you replaced the Yanmar belt guard after the upgrade, REMOVE IT NOW! These things do nothing but cook alternators.

You will be best to force cool air at the back of the alternator where the rectifier is. Inject it right into the vents of the black plastic cover.


My engine space is very compact, especially around the front of the engine. I'm thinking of ducting my engine room blower directly to the alternator - question is, would it be better to blow fresh air in toward the front, or suck air out from behind?
This alt is a dual internal fan unit. It sucks air in the back and from the front and expels it in the middle. The best way to help cool that alt is to force feed the back of the alt with cool air. Another blower sucking the hot air out of the TOP of the engine bay will also help.

Proper set up of any alternator includes running it at full bore via a dummy load (inverter & electric heater etc.) then closing the engine room and monitoring alt temp remotely. Reduce belt manager until the alt can run in the environment. You then back this up with the Balmar alt temp sensor as added insurance.

Please don't ever assume any small case alternator can run at full rated output for more than a few minutes, especially without external cooling. Some small case alts are better than others but they all need field reductions when fed into large loads. The only way I know of to run a small case alt at full bore is to remove the rectifier and rectify the alt remotely. Belt manager and additional cooling is a heck of a lot easier.

NOTE: Please note that EM has been know to install rotors with the rotor fins purposely bent so they don't have to do any additional machining to the alternator case. They also will sometimes run low temp wires right over the rectifier cooling fins which impacts cooling negatively and in some cases have cause melted wires.. The rectifier negative contact area is also not machined well, usually not at all, and can yield poor contact to the aluminum case which can also lead to poor cooling. They also don't tend to use heat transfer paste between the rectifier & case. These four issues can really impact cooling in a negative way.