Cooked Balmar AT-200

[Jd1]

This post is not to get input/advise, it is strictly to point out the limits of an AT-200 alternator.
For those that not aware, the AT-200 has a place for mounting a temperature sensor. When operated with an MC-614 regulator and the temperature sensor installed, the idea is to cut back on the alternator drive when the alternator gets too hot.
For some fools like me, who would like to push the envelope, this can lead to temptation. If field drive is set up to reduce output when the temperature gets too hot, people (ie me) might think that this covers all manner of setup sins. Alas, it does not .... and it turns out that this will probably be a $300 lesson.
The temperature probe attaches to the alternator case as mentioned before. I do not believe (although I do not have the alternator in front of me) that there is a good thermal path between the rectifier diode assembly and the alternator frame. The diode pack has a massive heat sink and I believe the thought was that it would never over-heat.
I used to run an MC-614 regulator and had the belt manager set up for significant de-rate (do not recall exact figure) and all was well except for when the temperature of the alternator went up too high - the MC-614 would cut output by 50%. The system would oscillate between the belt-manager limited output until the temperature would get up there and then drop output by 50%, cool and start the whole thing over. Obviously I did not de-rate the system enough but what could be the harm since the regulator would cut back drive automatically.
Some people have suggested that the MC-614 offers a gradual cut-back in drive based on temperature but according to Balmar and according to my experience that is NOT the case. I even confirmed that the regulator has the latest firmware - it does.
Anyway, back to the oscillating scenario .... I didn't like it. Surely there must be a better way ... and there is. Problem is, a better regulator also puts more responsibility on the operator and I abused that privilege. I ass-u-me-d that if we watch the alternator temperature, I could drive the regulator at full power as long as the drive gets cut back when things get too warm. In theory that works, in real life not so much
Anyhow, to make a long story short, I believe that the temperature measurement on the alternator frame does not reflect the temperature on the diode pack and if one drives the crap out of the regulator the diode pack will start sizzling nicely shortly after the alternator starts putting out 200A and while the frame is still nice and cool.
I never exceeded 104C frame temperature but looking at the diodes, it is clear that they were pushed well beyond that.
The tests I was running were with no forced air cooling and the tests were run to verify the cutback of alternator drive as temperature increased. As mentioned, even with the the case temperature well within operating parameters, it is still possible to fry the alternator. I am starting to wonder how effective forced air cooling will be for the rectifier pack. In any case, I have lost the confidence that the temperature sensors provides an accurate reading of all the components and as such I will not tune for maximum output with cooling but rather for acceptable output with no cooling and the additional cooling I supply will only enhance the life of the components rather than enabling me to increase output.
The lesson learned: increase drive gradually until you reach the maximum output at a safe temperature. Give the system plenty of time to reach a steady state temperature. Use the thermal sensor as a safety and not a means to increase overall output.

Has anyone succeeded in removing the diode pack from an alternator and mount/cool it separately ?

[Ostinato]

I concur with your conclusion that on the Series 6 at least the sensor monitors only the case temperature. I'll be curious if anyone has mounted the rectifier remotely. Sounds like it might require a separate cooling system. BTW rectifiers for Series 6 at least are only about $70. They can be purchased separately or as part their "ocean" rebuild kit. Something similar may be available for your model.

[Jd1]

I am looking at $165 (CAN) for the rectifier assembly from the repair shop, probably around $80 air freight and $60 or so for install of the rectifier assembly in the alternator.
I found the ocean rebuild kit for 225 US on the internet but have not found the rectifier assembly by itself. The alternator has only about 300 hours on it so I do not need the bearings and brushes.
I have asked for the old parts back in the hopes that I might be able to match just the diodes and build a spare diode pack. Not sure if that is realistic or not.

[Ostinato]

Call Balmar. They'll put you with a distributor that can sell just the rectifier.

[a64pilot]

From what I know, your pretty much correct in your statements.
Mark Grasser does / can and I believe will remote mount the diodes, forced cooling will help a little, best to blow air into the rear of the alt not the front.
Bottom line, these are small frame alternators and as you have noticed their cooling is limited, if you want high amperage you pretty much have to go to a BIG alternator designed from the beginning for that, like a school bus alternator, Military alternator etc.
Just my opinion of course, it can make 200 amps, they didn't lie, just they didn't tell you at what duty cycle it can be driven to 200 amps is all.

[DeepFrz]

There was a thread about 6 months ago where someone was having a problem with their alternator overheating. The person posted a picture and it was obvious to me that the alternator was crammed into a space that very much restricted cooling air flow. I suggested that he add a fan and when he did that the overheating problem was gone. I think that in small engine rooms high output alternators require a fan to keep them operating within their temperature limits. Either a fan or moving the diodes away from the alternator as you and a64pilot have suggested. Even when the diodes are removed from the alternator case they may still require a fan to assist with the cooling.

[Stu Jackson]

What kind of load were you trying to drive? I have a nom. 400 ah house bank. After a night on the hook running the fridge, my MC-612 wants to run full bore. Instead of programming a derating, which I find bassackwards, I use the Small Engine Mode, a simple toggle switch on the regulator, until the amps out on my Link 2000 get down to 30A, I turn off the SEM and it kicks up to 60A, on my 100A alternator.

If you are continually running a 200A alternator to the point it heats up, it may be time to investigate other methods to "control" your output and load on the system.

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]

[senormechanico]

I believe MainSail has done some testing with remote mounted diodes.
There was a thread which contained a post from him about it.
Check his website.
compassmarine.com

[deluxe68]

I am having the same issue with my 165. I de-rated it 28% and still having problems. During bulk mode at 2000 rpm it puts out 130 amps, then drops to 60 after 5 minutes. A few minutes later it is back up to 110 amps then after a short time it drops again.

[Maine Sail]

Originally Posted by Jd1

The lesson learned: increase drive gradually until you reach the maximum output at a safe temperature. Give the system plenty of time to reach a steady state temperature. Use the thermal sensor as a safety and not a means to increase overall output.

I have been urging folks to do this for at least 15+ years..

#1 Belt Manager - as primary thermal protection
#2 Temp Sensor - as your insurance policy

I go into a lot of this in the article below. Just scroll to where alternators are discussed.:

https://marinehowto.com/lifepo4-batteries-on-boats/

Originally Posted by Jd1

Has anyone succeeded in removing the diode pack from an alternator and mount/cool it separately ?

I run a small case alt with an external rectifier, it's built by Mark Grasser. I no longer use Belt Manager and only use the alt temp sensor as added insurance. I am pretty sure Mark could convert an AT200 to external rectification..

The alternators AC output uses 6GA wire braided into a hair braid weave. It was then mylar foil wrapped and encased in the orange heavy non-split conduit for the path to the external rectifier. This was during the install & alignment process...



This is a Mark Grasser/CMI small case with external rectification.

[Jd1]

Originally Posted by deluxe68

I am having the same issue with my 165. I de-rated it 28% and still having problems. During bulk mode at 2000 rpm it puts out 130 amps, then drops to 60 after 5 minutes. A few minutes later it is back up to 110 amps then after a short time it drops again.

Assuming you are using the MC-614 for a regulator, that is the regulator dropping to 50% drive because the alternator is overheating. Once it cools, drive is restored .... and so on.

[Jd1]

Originally Posted by Maine Sail

I have been urging folks to do this for at least 15+ years..

#1 Belt Manager - as primary thermal protection
#2 Temp Sensor - as your insurance policy

Yup, I should have listened, it would have saved me a pretty penny!

[Maine Sail]

Originally Posted by Jd1

Assuming you are using the MC-614 for a regulator, that is the regulator dropping to 50% drive because the alternator is overheating. Once it cools, drive is restored .... and so on.

This regulator drops in steps but the time to each step is quite short if temp continues to rise. It can appear as an immediate cut to 50% but it's really a bunch of smaller cuts with short windows between each one.... You may also find that when it supposedly goes back to 100% it is no longer 100% as it is actually trying to find a sweet spot, something that is pretty tough to do with LFP due to the continual demand..

[Jd1]

Originally Posted by Maine Sail

This regulator drops in steps but the time to each step is quite short if temp continues to rise. It can appear as an immediate cut to 50% but it's really a bunch of smaller cuts with short windows between each one.... You may also find that when it supposedly goes back to 100% it is no longer 100% as it is actually trying to find a sweet spot, something that is pretty tough to do with LFP due to the continual demand..

I think we need to agree to disagree on this point. I have confirmed that my regulator has the latest firmware, Balmar has confirmed they do a single cut in drive and I have confirmed that with my setup that constantly plots output vs time.
I can only think that maybe you are looking at an unreleased version of the MC-614 that Balmar passed to you for evaluation ....

[transmitterdan]

Let's look at some numbers.

A typical 6 diode rectifier producing 200A DC puts 67A through each of 6 diodes. Peak currents can be higher but we'll ignore that for now. So we have about 1.2-1.5 V and 67A on each diode which is somewhere between 80-100W per diode. Typical junction to case temp is 1.5C/W so it means the silicon is 90-150C hotter than the case.

If you want those diodes to last you need to limit case temp a lot lower than 104C or run less current.

External mounting helps a lot. Forced air (or better yet liquid cooled) heat sink can maintain a much lower heat sink temp.