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Old 07-10-2017, 03:49   #61
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Re: Alternator cooling

I too would like to hear real world experiences with external rectifiers. I'm also stuck with a small frame alternator and over the years have gone from an Ample Power unit based on a GM 10DN alternator to a modified GM CS130 and now to a modified GM CS130D all with external 'smart' regulators with some improvement but no real success.

In another thread I wrote a note about airflow dirrection which I will copy here... "All the alternators I am familiar with have either a single fan on the front of the alternator (like a 10SI alternator https://alternatorparts.com/x10si.html), or a fan on the front and an internal fan (like a CS130 alternator https://alternatorparts.com/xcs130.html), or two internal fans (like a CS130-D alternator https://alternatorparts.com/xcs130d.html). All suck in from the back over the diode pack and blow out at the front or side. The fans are centrifugal. They suck at their center and blow out at their periphery." This is a picture of a GM CS130D alternator.

Of course, we are not the only ones worying about hot alternators. https://www.electronics-cooling.com/...r-electronics/
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Old 07-10-2017, 10:08   #62
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Re: Alternator cooling

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Originally Posted by wsmurdoch View Post
Of course, we are not the only ones worying about hot alternators. https://www.electronics-cooling.com/...r-electronics/
An interesting article! The one bit that I found especially interesting was that some diodes can run reliably up to 200C CASE TEMP. I had previously worked on 190C JUNCTION TEMP figures.
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Old 07-10-2017, 13:18   #63
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Re: Alternator cooling

I would be skeptical of any claims of reliable operation at 200C case temps. Even silicon carbide devices generally limit junction temps to 175C.
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Old 07-10-2017, 14:25   #64
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Re: Alternator cooling

That article was from 2002. I would expect some advancement since then. However I saw an interesting paper "Thermal Modelling of Lundell Alternators" and the temperatures were much lower than stated in the article. In this article winding and case temperatures dropped when the rectifier was located externally but the rectifier temps remained close to the internal readings. However in the modelling (at least the parts that I read) the ambient temp. was held at 20 deg. C which is much lower than I would expect to find in a typical sailboat engine room, or in an automotive engine compartment.

I suspect that many of the problems CF members have been experiencing of the alternators shutting down is because of high ambient temperatures in improperly vented engine rooms possibly (probably?) exacerbated by restricted air flow to the alternator.

The output of the alternator was held to approximately 110 - 112 amps. for this report.

Edit: I had not noticed the significant drop in diode temp. from an internally and externally mounted diode pack until I looked at the document a second time. This would alter my conclusion above such that removing the diode pack from the alternator would result in much higher alternator output before thermally throttling the alternator.
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Old 07-10-2017, 14:54   #65
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Re: Alternator cooling

Yes, getting the diodes outside with a decent heatsink greatly reduces thermal loading of the alternator.
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Old 07-10-2017, 15:49   #66
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Re: Alternator cooling

[QUOTE=a64pilot;2493779] My bet is that a larger crankshaft pulley and or a small alternator pulley would help.

Sure, look at Lycoming aircraft engines. The crank pully is 12" in diameter and they run the same rpm as a boat with automotive style alternators.
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Old 07-10-2017, 16:29   #67
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Re: Alternator cooling

I think a typical alternator max RPM limit is around 18,000 or so.
We need roughly a little less than a 6 to 1 ratio, varying on engine max RPM of course
I have never measured, but suspect we have about half that.
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Old 07-10-2017, 16:31   #68
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Re: Alternator cooling

[QUOTE=Guy;2494272]
Quote:
Originally Posted by a64pilot View Post
My bet is that a larger crankshaft pulley and or a small alternator pulley would help.

Sure, look at Lycoming aircraft engines. The crank pully is 12" in diameter and they run the same rpm as a boat with automotive style alternators.


I actually had never thought about that, but I believe your correct. However if memory serves the IO-520 in a Cessna 210 has a small primary drive pulley as itís on the back of the engine?
Wonder how much effect that has or if anything is different?
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Old 07-10-2017, 16:46   #69
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Re: Alternator cooling

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; I actually had never thought about that, but I believe your correct. However if memory serves the IO-520 in a Cessna 210 has a small primary drive pulley as it’s on the back of the engine?
Wonder how much effect that has or if anything is different?
That pulley runs faster than the crankshaft. It runs so fast that every once and a while you have harmonic problems and it throws a/c belts etc.
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Old 08-10-2017, 10:51   #70
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Re: Alternator cooling

Isn't this all a moot point as you are limited by the batteries ability to take a heavy charge for long? (unless you have a huge bank that is, and carrying a lot more capacity than your daily need , with margin, is just wasting room and weight)
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Old 08-10-2017, 16:25   #71
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Re: Alternator cooling

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Originally Posted by ErikFinn View Post
Maine Sail,
did you complete the "ripping the diode rack out & converting it to external rectification"?
If you did, how has it worked for you?
Thanks,
Erik

My small case alt is feeding a 400Ah LiFePO4 bank, in other word it never catches a break. I have had belt manager turned off since I did the conversion testing.. The peak recorded temp is 236F but in most cases it peaks out around 217F - 224F... The alt could previously exceed 300F in very short order unless I used belt manager and external cooling. With the conversion I did lose about 6-8A in peak output, even though I used 6GA wire between stator and external rectifier, but I consider that a fair trade off....
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Old 08-10-2017, 17:22   #72
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Re: Alternator cooling

Mainesail, do you advocate changing pulley size to increase alternator speed ?
I run my Westerbeke 55A at 1600rpm most of the time.
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Old 08-10-2017, 17:54   #73
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Re: Alternator cooling

Quote:
Originally Posted by Cheechako View Post
Isn't this all a moot point as you are limited by the batteries ability to take a heavy charge for long? (unless you have a huge bank that is, and carrying a lot more capacity than your daily need , with margin, is just wasting room and weight)


Even with regular AGM batteries that are at a full charge, itís nice to be able to run high amp devices when underway with the inverter, like a watermaker, or when itís stupid hot and no wind, I have been known to run my forward Stateroom AC so I can get some sleep when she is on watch during the day.
Be nice if the alternator could provide all the power necessary to do that.
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Old 08-10-2017, 18:10   #74
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Re: Alternator cooling

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Mainesail, do you advocate changing pulley size to increase alternator speed ?
I run my Westerbeke 55A at 1600rpm most of the time.
It certainly helps especially on slow turning diesels.. However, if your water pump is also driven by this belt then you can't just do the crank pulley. Mark Grasser is the only one I know of doing custom large dia serpentine kits. My own engine is on The to-do list but we've both been to busy to even get to it.. The external rectifier solved my heat issues but it would be nice to have full output at close to idle speed...
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