Alternator Overheating Problem

[Andina Marie]

If you are using a diode splitter they are very bad for alternator load. They charge the LOWEST battery first, then when its voltage gets to the next lowest it ADDS that load to the alternator. On boats we typically have way more battery size than the OEM alternators were intended to handle so if both batteries are low you can severely overload an alternator. When it heats up the output and efficiency drops making it worse. If you replace the splitter with a Combiner100 it will regulate the amount of current delivered to the house battery to a safe level within the capacity of the alternator. This stops the alternator overheating so it can maintain a higher output.

[SV Demeter]

Originally Posted by DeepFrz

Absolutely agree. I just said that a temp. sensor is not the answer to his problem. Neither is cutting down the size of his battery bank. The temp. sensor should be used, I agree, but the problem is he has an alternator that is to small. Not to small for his battery bank, but to small for his electrical usage. Charge more often for a shorter period of time until they can upgrade the "system".

Spot on here DeepFrz. Im guessing though that based on the OPs budget contraints a new alternator is not in the cards. As for the temp sensor my understanding at least for the Balmar 614 is that it will reduce output based on temp to allow the alt. to put out max amps without exceeding a specified alt temp. Not sure what the sterling system does. Also not sure the sterling regulator has a small engine mode. Sort of guessing that the OP may have moved on as well based on responses...

[donradcliffe]

Originally Posted by Andina Marie

If you are using a diode splitter they are very bad for alternator load. They charge the LOWEST battery first, then when its voltage gets to the next lowest it ADDS that load to the alternator. On boats we typically have way more battery size than the OEM alternators were intended to handle so if both batteries are low you can severely overload an alternator. When it heats up the output and efficiency drops making it worse. If you replace the splitter with a Combiner100 it will regulate the amount of current delivered to the house battery to a safe level within the capacity of the alternator. This stops the alternator overheating so it can maintain a higher output.

This is completely and absolutely rubbish--ignore this advice.

If your alternator is quite hot, the first thing to do is check for belt slippage--the pulley end of the alternator will be hotter if this is your problem.

Since you had a problem with the battery selector switch melting, you may have had an overvoltage on the alternator and failed one or more output diodes. However, if it puts out over 2/3 of its rated current when cold, that's not likely the problem.

If the belt is good, car alternators are not designed to run long periods at the rated output, so you should either cut the charging rate or find a better alternator.

[MarkSF]

My understanding is that most automotive alternators already have some temperature compensation built in. This is not to protect the alternator but rather the car's battery. They make an assumption that the car's battery and the alternator are at more or less the same temperature. So the alternator puts out a higher voltage cold than when hot. This way charging when cold is maximised without danger of overheating the battery on a hot day.

This may be the reason you are seeing the current dropping. It's dropping as the alternator gets hot and reduces the o/p voltage, as designed. You could check that with a meter.

I think the other posters have covered why the alternator is overheating.

[DeepFrz]

SV Demeter;

As for the temp sensor my understanding at least for the Balmar 614 is that it will reduce output based on temp to allow the alt. to put out max amps without exceeding a specified alt temp.

It doesn't really say by how much it reduces the output. The manual for the 612/ARS-5 states it cuts output by ~50%. It also states that although that will protect the alternator it isn't the answer to the problem.

http://www.balmar.net/PDF/2009-12V-a...manual-web.pdf

The following is the quote from the 614 pdf. It does allow you to program temp limits for over temp.

Alternator Temperature Sensing: automatically reduces
regulator field output when alternator temperature exceeds
set limits. Over-temperature condition activates dash lamp
circuit. Requires optional Alternator Temperature Sensor
(MC-TS-A) to enable temperature sensing functions

[Stu Jackson]

If you read the rest of the manual, read the Small Engine Mode. It uses these same connectors and cuts the output to 50%. The sensor is just a switch, on/off. If it sense higher alternator temperatures, is drops output to 50%. That's all.

[DeepFrz]

Stu, the idea isn't really to run an alternator at 50% output. The idea is to run the alternator at as near full output as possible in order to get the batteries charged, n'est-ce pas?

[Maine Sail]

Originally Posted by donradcliffe

This is completely and absolutely rubbish--ignore this advice.

If your alternator is quite hot, the first thing to do is check for belt slippage--the pulley end of the alternator will be hotter if this is your problem.

Since you had a problem with the battery selector switch melting, you may have had an overvoltage on the alternator and failed one or more output diodes. However, if it puts out over 2/3 of its rated current when cold, that's not likely the problem.

If the belt is good, car alternators are not designed to run long periods at the rated output, so you should either cut the charging rate or find a better alternator.

Don,

With all due respect please explain to us why what the owner of Yandina Marine Electronics posted is rubbish? You can't simply slam someone as posting rubbish then not explain why. I would love to hear your explanation.

Our own boat had a Yandina Combiner 150 installed for 2800 engine hours and used a 50A stock Mitsubishi dumb regulated alternator. That little alt is still kicking and we now have a 375 Ah bank......

[Kapena]

Proper sizing for an alternator is 25% of amp hour capacity. That is the recommended maximum charge rate for lead acid batteries. You have 300 amp hour capacity, alternator should be sized at about 80 amps. Nothing wrong with the size of your alternator. The internal battery resistance sets the charge rate. Its the same reason current drops as you charge the batteries.

I won't get into splitters and combiners but you should use the term isolators as they are intended to isolate a path.

Steps to determine your problem. Measure the voltage output of the alternator (the big wire). If it's above 14 volts, when the current output is low, then measure the voltage at the batteries.
1) Good at alternator, bad at batteries then the splitter/isolator is your problem.
2) Good at both regulator and batteries then the batteries are toast. (My choice as you depleted them way too far (<50%)... this is not reversible).
3) Low voltage at alternator then continue to next

If the voltage output is low at alternator (big wire) then measure the regulator voltage.
1) Voltage at regulator (small gauge wire running to alternator) low (<8 volts)? Bad regulator. You can further test this by DISCONNECTING this wire from the alternator then shorting the alternator connection (not the regulator) to the big wire at the alternator. This causes the alternator to have maximum output.
2) Regulator Voltage good,at regulator, then alternator is bad. Check diodes (also a prime candidate for this problem).

Its that easy.

[Stu Jackson]

Originally Posted by DeepFrz

Stu, the idea isn't really to run an alternator at 50% output. The idea is to run the alternator at as near full output as possible in order to get the batteries charged, n'est-ce pas?

Oui!

It's an interesting set of operational options, most ALL of which has been INITIATED to save the belt from squeaking or chewing. :

1. Run your alternator output at less than 100% with amp manager, but NOT as far down as to 50%, so all the time your engine is running your AO is less than what you've installed, even after the bulk phase is over. If you have an alternator temperature sensor installed, if the alternator even then gets hot, it cuts it back that preset reduced level to 50% of that.

2. Use the Small Engine Mode for initial startup. Then manually switch back. Disadvantage is manual, of course. But I've found it's only for the first half of the bulk phase/stage from the regulator (23 or 30 or 36 minutes) that I can kick it right back up. This avoids belt chewing at startup, even with the delayed, soft start on the regulator. Then after 10 minutes or so, I get the highest AO that the batteries can accept. Not foolproof, does require switching and managing, but I like doing that and it gets me to keep checking the system, which I enjoy anyway. I'm always up and down checking the Link 2000 and other stuff anyway.

3. It could be that folks do both, but I doubt it. Most aren't aware of SEM, or don't think it applies to them and can be used, and/or just get "into" the reed switch instructions and work from there. The SEM presentation doesn't hint at using it the way I do.

I could, but haven't, installed an alternator temperature sensor, although I could in parallel with the SEM switch. - Disadvantage is my alternator could get hot, but since I do it manually, the switch is right where the alternator is (two small doors in the head, one for the switch, one for the alternator access - we have an aft head right by the engine.

Yes, good food for thought on the different ways to approach the issue.

[foggysail]

Originally Posted by Kapena

Proper sizing for an alternator is 25% of amp hour capacity. That is the recommended maximum charge rate for lead acid batteries. You have 300 amp hour capacity, alternator should be sized at about 80 amps. Nothing wrong with the size of your alternator. The internal battery resistance sets the charge rate. Its the same reason current drops as you charge the batteries.

Its that easy.

One must be careful using so called "rule of thumbs." An alternator will heat up because of the output current passing through the internal DC wire resistance. There are also core losses in the armature metal but the largest loss is in the internal wiring. Note--- there is some AC affect also such as skin affect because an alternator is an AC machine with rectified output.

The charge current is directly related to (alternator output voltage minus the battery voltage)/ total circuit resistance that includes the internal battery resistance. So there will be heating in both the alternator and the battery being charged. An unloaded alternator can easily output voltages as high as 100vdc if the field is highly excited.

Note that the alternator acts like a constant voltage source, not a constant current source.

One final comment on the melted battery switch. My guess ........ and its only a guess is that the likely cause was a loose wire connection that generated the heat.

Foggy

[Kapena]

Foggy. I did not use a "rule of thumb". I used the battery manufacturer recommendations. Look it up.
AN unloaded alternator will typically output a maximum of 22 volts, many only 18v. The stator core saturates. Try it. 18 to 22 volts is enough to fry some 12v electronics which is why you don't switch the battery switch with the engine running.
Skin effect is the depth in the wire that most of the current is conducted (proportional to frequency). It has no effect on AC (except as resistance). It has no meaning to this discussion. Nor does copper losses, voltage sources, number of poles or phase of the moon. I gave him information how to trouble shoot his problem and what to fix.

[foggysail]

Originally Posted by Kapena

Foggy. I did not use a "rule of thumb". I used the battery manufacturer recommendations. Look it up.
AN unloaded alternator will typically output a maximum of 22 volts, many only 18v. The stator core saturates. Try it. 18 to 22 volts is enough to fry some 12v electronics which is why you don't switch the battery switch with the engine running.
Skin effect is the depth in the wire that most of the current is conducted (proportional to frequency). It has no effect on AC (except as resistance). It has no meaning to this discussion. Nor does copper losses, voltage sources, number of poles or phase of the moon. I gave him information how to trouble shoot his problem and what to fix.

Well, you're right, the phases of the moon have no effect on alternator losses. My earlier post intended to describe the causes of internal heating which have little to do with the size of the battery being charged. But an alternator's size for an application would be better provided by the alternator manufacturer rather than a rule of thumb from a battery manufacturer. In this case, bigger is better!

This is not rocket science but it is engineering.

[DeepFrz]

Here is some good news for those with hot engine rooms...and its not really new news.

http://www.prestolite.com/literature...i_temp_alt.pdf

[hellosailor]

crazyhorse-
"The alternator is from a nissan car,"
That explains a great deal.

My first question would be to ask if anyone knows, for a fact, what rpm the alternator is designed to run at, and if the pulley was correctly sized to prevent the alternator from revving too high in the boat installation. Run it too fast, and it can overheat and burn out. They all have a rating for shaft rpm and power output.

Then it comes back again to being a car alternator. They're rated for an output that is really expected for only a few minutes, not a constant output rating. In a car system the regulator quickly cuts back from full power to half power so the alternator may be rated "80A" but that's with the expectation that it won't need to run at full power for more than maybe 10 minutes. It can't shed heat if run at full output.

And as a car alternator, it again expects to see gobs of fresh air blowing through the engine compartment at road speeds--in a boat, it definitely will need cooling assistance.

But even with extra cooling? And correct rpm matching? I wouldn't expect it to put out more than 50A for any length of time without overheating. When all is said and done--it just wasn't designed and rated for this application. That's part of why a marine alternator, designed for long-term rated high power output, is going to be more expensive. I'd vote for replacing this one with something designed for the job at hand--and picked by someone who knew how to match up the shaft speed as well, to make sure it was used effectively whatever it was.