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Alternator temperature


Dr Bob

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1 hour ago, Tony Brooks said:

I think this statement is not the whole truth but is near enough the truth for most purposes..

 

Yes, for years we have said alternators are self limiting for current and so they are as long as you stay within their design parameters. They still self limit when you are outside those parameters but the self limiting comes from the Watts = Amps X Volts. Unless Leece Neville have a shunt in their output so the regulator can "measure" the output current the regulator can not control it, So the question is if what Leece Neville told you is true what mechanism controls the current? Until I see a definitive explanation this comes back to the Watts thing.

 

So lets have the answer for how do they  control their current when operating way outside their design parameters.

 

For goodness sake, don't they ever learn. We had enough trouble with the aluminium would starters, now they   have done it to alternators as well.

There is no limitation specifically on power from one of these alternators other than that the voltage is regulated and the current self limits. The current self limiting will largely be a limitation of the electromagnetic design of the machine; the size and flux density in the rotor and stator (there is an interaction with the regulator, more rotor current can give some more power in some circumstances). This is why a higher rated alternator is physically bigger than a smaller rated unit, it has a much bigger magnetic circuit. The "Watts thing" is what appears to happen as a result of regulation of the volts and self limiting current. You could get a much larger rating in Watts if you removed the voltage regulation, applied full rotor current and ran the alternator at the same speed. 

 

All machines will have a limitation, it may be that some older devices can overcorrect if they had poorly designed magnetic circuits (i.e. too much material) but modern designs with a focus on cost and weight reduction are likely to be only just big enough to generate the design current.

 

Perhaps this is something that can be demonstrated, I will see what happens when I load up my alternator with a discharged battery and a fully loaded inverter. My judgement is that the current will not greatly exceed the manufacturer's published rating. 

Edited by jonesthenuke
Typos!
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8 hours ago, bizzard said:

A wee computer fan could be mounted directly behind the alternator to add extra boost to the alternators fan. But the engine compartment does need decent vents to the outside or the fans just keep recirculating  hot air.

Thanks Bizz. I will have a look at more cooling in the summer once it warm up a bit. Can't see any ventilation holes in the engine hole other than the gaps around the 'lid'. 

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7 minutes ago, jonesthenuke said:

There is no limitation specifically on power from one of these alternators other than that the voltage is regulated and the current self limits. The current self limiting will largely be a limitation of the electromagnetic design of the machine; the size and flux density in the rotor and stator (there is an interaction with the regulator, more rotor current can give some more power in some circumstances). This is why a higher rated alternator is physically bigger than a smaller rated unit, it has a much bigger magnetic circuit. The "Watts thing" is what appears to happen as a result of regulation of the volts and self limiting current. You could get a much larger rating in Watts if you removed the voltage regulation, applied full rotor current and ran the alternator at the same speed. 

 

All machines will have a limitation, it may be that some older devices can overcorrect if they had poorly designed magnetic circuits (i.e. too much material) but modern designs with a focus on cost and weight reduction are likely to be only just big enough to generate the design current.

 

Perhaps this is something that can be demonstrated, I will see what happens when I load up my alternator with a discharged battery and a fully loaded inverter. My judgement is that the current will not greatly exceed the manufacturer's published rating. 

Been pondering this a bit more. I agree now. The magnetic fluxes will be the result of amp turns, so nothing to do with power. However I still can't understand how a nominal 70 amp alternator can produce well over 80 amps (runs out of ammeter scale) at first start up if they are totally self limiting.

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7 hours ago, Boater Sam said:

 

Diode pack and regulator should be good to 120 degrees C, the enamel insulation on the windings will be 150 degree stuff, it all has been for many years. I wind transformers and that's all I can buy these days.

 

But the temperatures outside will be different than the inside by quite a margin.

 

 

Thanks Sam for that info.

I think that makes me happy with the temps I am seeing. How much difference do you guess between inside and outside? It's only 50C on the back of the alternator so the diodes will be ok at today's temps.

I will measure the temp rise on the alternator today after running it at 55A for an hour then turning off the engine. I know it goes up a wee bit but I think it only 10C ish. That will give me a clue to the internal temp of the windings.

 

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Some may be wondering what the flux this is all about.

Look at it this way, if the alternator fails in the near future, is it a good make? How old is it? How much work has it done? Does it owe you much?

Will a new good one like a Leece Neville Prestolite one break the bank?

 

The economy of materials in cheap alternators limits the maximum flux possible which is why they seldom give out their full rated output.

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1 minute ago, rusty69 said:

If only such a device existed. This time next year we could be squillionaires biscuits!

We would have to come up with a "greenwash" marketing strategy first though.  Maybe we could pretend that putting them on top of coal fired stoves was in some way eco-friendly.

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4 minutes ago, TheBiscuits said:

We would have to come up with a "greenwash" marketing strategy first though.  Maybe we could pretend that putting them on top of coal fired stoves was in some way eco-friendly.

Don't be stoopid,they would melt!

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Don't run the engine too slowly when charging the batteries. The alternator will run slightly cooler at higher engine revs because the fan will shift more air.

 

My Beta 43 has the 175 amp alternator fitted. I hate to think how hot it could get. On start-up I've seen 185 amps for a minute or so, and it often provides over 150 amps for at least half an hour into my 4 leisure batteries. To help it keep cool under the cruiser deck, when there was a spare hole caused by having to move the exhaust outlet from one side to the other, I attached some trunking to that hole with a bilge blower fan wired to the "ignition" circuit to blow cool air straight at the alternator. At all engine speeds up to 2500 rpm you can feel the excess air coming out of the grill that used to be the only air inlet to the engine bay. The whole engine bay runs at least 10-15 degrees cooler with the fan.

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1 hour ago, Keeping Up said:

Don't run the engine too slowly when charging the batteries. The alternator will run slightly cooler at higher engine revs because the fan will shift more air.

 

My Beta 43 has the 175 amp alternator fitted. I hate to think how hot it could get. On start-up I've seen 185 amps for a minute or so, and it often provides over 150 amps for at least half an hour into my 4 leisure batteries. To help it keep cool under the cruiser deck, when there was a spare hole caused by having to move the exhaust outlet from one side to the other, I attached some trunking to that hole with a bilge blower fan wired to the "ignition" circuit to blow cool air straight at the alternator. At all engine speeds up to 2500 rpm you can feel the excess air coming out of the grill that used to be the only air inlet to the engine bay. The whole engine bay runs at least 10-15 degrees cooler with the fan.

Thanks KU. Interesting to hear. I'm not even sure if we have an air inlet to the engine bay. I must have a look.

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2 hours ago, TheBiscuits said:

It's a shame nobody makes a type of fan that spins faster the hotter it gets ...

An ecofan bolted directly to the alternator is obviously the answer, not only does it go faster the hotter it gets but its Peltier module actually sucks heat out of the alternator to drive its motor ?

 

I have tried cooling my alternator with a good (Caframo) fan and did not achieve much. Ducting in cold air to the alternators own fans might achieve more, a few installations do do this.

 

Compared to the fans in the alternator the extra flow from a computer fan is likely almost negligible.

 

................Dave

 

 

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5 minutes ago, Dr Bob said:

Thanks KU. Interesting to hear. I'm not even sure if we have an air inlet to the engine bay. I must have a look.

Air must be getting in somewhere or the engine would have suffocated through lack of breath through the inlet manifold. But until that happens a terrible vacuum in the engine space can happen causing alsorts of damage, like caving inwards of hull sides and bulkheads until the engine hasn't the strength to suck anymore and expires. Experienced many times in WW2 diesel electric submarines during emergency dives, when the engineers were caught napping and shut the engines down too late after the conning tower manhole lid had been closed. The whole inside of the boat would be subject to an almost instant vacuum caused by the diesels gasping for air. This terrible vacuum had a gastly effect on the crew, causing SCEB '' severe Chronic expansion bloatage'', popping out eyeballs and other horrific maladies, things too awful to describe here.

  • Haha 1
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1 minute ago, bizzard said:

Air must be getting in somewhere or the engine would have suffocated through lack of breath through the inlet manifold. But until that happens a terrible vacuum in the engine space can happen causing alsorts of damage, like caving inwards of hull sides and bulkheads until the engine hasn't the strength to suck anymore and expires. Experienced many times in WW2 diesel electric submarines during emergency dives, when the engineers were caught napping and shut the engines down too late after the conning tower manhole lid had been closed. The whole inside of the boat would be subject to an almost instant vacuum caused by the diesels gasping for air. This terrible vacuum had a gastly effect on the crew, causing SCEB '' severe Chronic expansion bloatage'', popping out eyeballs and other horrific maladies, things too awful to describe here.

I never know when you are joking. April 1st is another week or so. 

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14 minutes ago, rusty69 said:

I never know when you are joking. April 1st is another week or so. 

The air intakes on those big diesels were as big as dustbins with tremendous suction, quite capable of sucking in the crew members, the entire crew if the water tight door in the engine room had been left open, to be tumbled about a bit and finally ejected from the exhaust pipes slighty burnt around the edges.

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On 22/03/2019 at 09:26, MoominPapa said:

These seem quite conservative numbers. I run an 70A (nominal) A127 at 65A for hours on end and have not yet had a failure. I'd expect a 90A alternator to have better cooling.

 

 

MP.

 

Interesting iv popped a couple of 127 clones in the last few years all heat related failures.

 

i now have sufficient spares that when the last one popped at stone with no factor near i just made one out of 3 ( had to borrow my wifes soldering iron)

 

i suspect mine go through a combination of slow reving and high load but i never see more than 30 a  for a prolonged period.

are you using clones or the real deal?

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  • 6 months later...

Dr Bob: what did you conclude about your alternator temperature measurements?  As I'm thinking of a hybrid system (see your other thread about the "affordable way to add lithium batteries" etc.) I intend to do some measurements of the alternator temperature when charging the existing LA bank first, to get an idea of the normal working temperature.  Obviously charging an extra 100-120Ah Li bank in parallel with the existing LAs (345Ah) is likely to work the alternator a lot harder.

 

In fact I spoke to Beta about this and they said that at least one boater had experienced an alternator that got hot enough to set off a fire(?) alarm when they installed a bank of lithium batteries, but I don't know how large a bank that was, so they were somewhat negative about the whole idea.

 

On the other hand, I was somewhat encouraged to see the comments from Boater Sam to the effect that the Iskra altenator should be quite happy at fairly high temperatures - they must be self-regulating to some extent when you consider the large variation in sizes of boat battery banks and the low SOC that some people run down to - but in any case my idea was to add a digital thermostat device (of a kind that's pretty cheap on Amazon and can go up to 120 deg C) to open a suitable relay and just disconnect the LI bank if the temperature should rise above the desired limit.

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