Alternators - Safe running temperature question

[stuhaynes]

This is a follow on from a previous thread, but please bear with me. I've already had the panels advice about small battery bank and getting a bigger alternator.
To recap

24 volt system
220AH domestic battery bank
65 amp alternator

Tested the system for the first time this morning, everything appears to be working perfectly. Turn on inverter...

Asked Kath to switch on immersion, fully expecting the alternator belt to screech, and the engine to complain. Not a bit of it! Engine didn't miss a beat, belt remains silent.

Inverter shows 40 amp load
Ammeter (brand new 60-0-60) actually shows a 30 amp positive current flow.
Great! We've cracked it! Immersion working and batteries charging too(?)

Drat! Fly in the ointment! The alternator is getting very hot. Switch off quick!

My questions to the panel are:

How hot do alternators get? After about 3 minutes of load I couldn't hold the back of my hand on the casing for more than a few seconds.

The first thing that the current from the alternator meets is the ammeter.
What does the +30 amp reading actually represent? The inverter draws its power directly from the leisure bank.

__________________________________________

Most of the time we are on shore power. The immersion thing is only for periods when we're away for a few days. Based on your previous advices and the fact that we don't have the space (or spare cash) for a massive battery bank and a 150 amp alternator, we've decided to buy a smaller immersion element, 500 watt to replace the existing 1KW unit. Bearing in mind that it would only be used either on shore power or while the engine was running what is the panels view? I don't want to damage the equipment, or turn the drive belt to spaghetti through excessive heat.

Many thanks, as always, Stu

 

[westernman]

My engine cooling system is plumbed such that it will heat up the hot water tank. I would have thought that is much better than trying to do it with electrickery when not on shore power.

 

[stuhaynes]

My engine cooling system is plumbed such that it will heat up the hot water tank. I would have thought that is much better than trying to do it with electrickery when not on shore power.

Unfortunately this is not possible at this time because of an engine plumbing problem that causes the engine to run very cool. I do intend to fix this, probably over the winter, but we want a couple of weeks away this season, hence our reliance on the electrics. I do agree with you though, this would be my first choice too if it were possible.

 

[BGW]

Inverter shows 40 amp load
Ammeter (brand new 60-0-60) actually shows a 30 amp positive current flow.
Great! We've cracked it! Immersion working and batteries charging too(?)

If the inverter is drawing 40 amps but the Ammeter shows only a 30amp charge rate, surely you are depleting your batteries by 10Ah, not charging them?

 

[Rigger Mortice]

Inverter is taking 40amps, and ammeter showing +30 amps implies that the alternator is putting 70amps into the system.
As it is rated as a 65amp alternator it is being pushed to the limit, which is why it is getting hot.

 

[VicS]

If the inverter is drawing 40 amps but the Ammeter shows only a 30amp charge rate, surely you are depleting your batteries by 10Ah, not charging them?

Inverter is taking 40amps, and ammeter showing +30 amps implies that the alternator is putting 70amps into the system.
As it is rated as a 65amp alternator it is being pushed to the limit, which is why it is getting hot.

Which explanation is right rather depends upon how the ammeter is wired into the circuit

if this is correct
"The first thing that the current from the alternator meets is the ammeter.
What does the +30 amp reading actually represent? The inverter draws its power directly from the leisure bank."
the first explanation is correct but one then has to wonder why with a 10 amp net load on the battery a 65 amp alternator is only producing 30amps.

If the second is correct one has to wonder how a 65 amp alternator is producing 70 amps

 

[Heckler]

This is a follow on from a previous thread, but please bear with me. I've already had the panels advice about small battery bank and getting a bigger alternator.
To recap

24 volt system
220AH domestic battery bank
65 amp alternator

Tested the system for the first time this morning, everything appears to be working perfectly. Turn on inverter...

Asked Kath to switch on immersion, fully expecting the alternator belt to screech, and the engine to complain. Not a bit of it! Engine didn't miss a beat, belt remains silent.

Inverter shows 40 amp load
Ammeter (brand new 60-0-60) actually shows a 30 amp positive current flow.
Great! We've cracked it! Immersion working and batteries charging too(?)

Drat! Fly in the ointment! The alternator is getting very hot. Switch off quick!

My questions to the panel are:

How hot do alternators get? After about 3 minutes of load I couldn't hold the back of my hand on the casing for more than a few seconds.

The first thing that the current from the alternator meets is the ammeter.
What does the +30 amp reading actually represent? The inverter draws its power directly from the leisure bank.

__________________________________________

Most of the time we are on shore power. The immersion thing is only for periods when we're away for a few days. Based on your previous advices and the fact that we don't have the space (or spare cash) for a massive battery bank and a 150 amp alternator, we've decided to buy a smaller immersion element, 500 watt to replace the existing 1KW unit. Bearing in mind that it would only be used either on shore power or while the engine was running what is the panels view? I don't want to damage the equipment, or turn the drive belt to spaghetti through excessive heat.

Many thanks, as always, Stu

I have the std Valeo 60amp alternator on my MD22. I put a Sterling alternator booster on it. The Nasa BM1 battery monitor shows the charge. I have a 440 AH domestic bank that I use all the time, the engine battery being reserved for emergencies.
I have only ever seen 15 - 20 amps charging because my bank keeps me well up in the power stakes. After I fitted the Sterling I did the same as you and put my hand on the alternator when it was charging, it was hot enough to make me take it off quickly. It has been like this for 2 years now. It seems as if it is not a problem, it seems to be normal.
Stu
PS the 30 amp charge is the engine trying to keep up with the invertor draw, do a quick calculation, the calorifier 500 watts? on 240 volts = 2 ish amps. On 24v = 20 amps ish. OK a bit simplistic but bottom line, a watt is a watt, the voltage determines the amperage. Your invertor is showing 40 amps then if the alternator is showing 30 amps then you have a deficit of 10 amps.
PPS must catch up quicker at the back!

 

[john_morris_uk]

Which explanation is right rather depends upon how the ammeter is wired into the circuit

if this is correct
"The first thing that the current from the alternator meets is the ammeter.
What does the +30 amp reading actually represent? The inverter draws its power directly from the leisure bank."
the first explanation is correct but one then has to wonder why with a 10 amp net load on the battery a 65 amp alternator is only producing 30amps.

If the second is correct one has to wonder how a 65 amp alternator is producing 70 amps

Futhermore, the alternator will be DE-RATED by the heat. The 65 Amp rating that the manufacturer gives is for the very best of ideal conditions - if you see what I mean. Heat is one of the things that will de-rate it. I would be very surprised to see much more than 50 amps out of the alternator on a regular basis. Depending on the accuracy of the meter etc it could easily be only '30 amps'...

 

[stuhaynes]

I have the std Valeo 60amp alternator on my MD22. I put a Sterling alternator booster on it. The Nasa BM1 battery monitor shows the charge. I have a 440 AH domestic bank that I use all the time, the engine battery being reserved for emergencies.
I have only ever seen 15 - 20 amps charging because my bank keeps me well up in the power stakes. After I fitted the Sterling I did the same as you and put my hand on the alternator when it was charging, it was hot enough to make me take it off quickly. It has been like this for 2 years now. It seems as if it is not a problem, it seems to be normal.
Stu
PS the 30 amp charge is the engine trying to keep up with the invertor draw, do a quick calculation, the calorifier 500 watts? on 240 volts = 2 ish amps. On 24v = 20 amps ish. OK a bit simplistic but bottom line, a watt is a watt, the voltage determines the amperage. Your invertor is showing 40 amps then if the alternator is showing 30 amps then you have a deficit of 10 amps.
PPS must catch up quicker at the back!

The load is from a 1KW immersion heater (at 230 volts) so the (approx) 40 amp load is about right for 24 volts.

I've considered lots of things, mainly about conserving the alternator and batteries and have decided to swap the existing immersion heater for a 500 watt one, 21 amp load instead of 42. Surecal mention them as an option, so I've emailed them. The panels view about this lighter load will be most welcome. Why is electrickery so bloody difficult to grasp? That is not an invitation for the obvious joke..... Oh go on then...

 

[Gypsy]

You have not mentioend the revs of the engine when you are doing this. Remember the 65A rating is the maximum output of the alt at IT'S rated shaft revs, which are subject to the ratio of the pullys on the engine crank and alt shafts.

As a separate matter, Balmar set their regulators to limit the Alt output when the temp gets to 110-115C as sensed by their thermistors attached to the alternator frame. It is 'B' hot and could perhaps boil water but I have also seen others suggest that 120C is OK. So much depends upon the airflow available in the engine compartment and/or if the alt has a fan which is part of the pully side arrangement.

 

[Avocet]

If it helps, I once saw 175 degrees C on a car alternator that was undergoing some (pretty extreme!) testing. I certainly wouldn't worry at all up to 100 C and probably (as the previous poster says) to 120. Obviously, cabling needs to be routed to as not to be directly in constact with the body - I think the insulation can soften quite significantly at 120C.

 

[BGW]

The load is from a 1KW immersion heater (at 230 volts) so the (approx) 40 amp load is about right for 24 volts.

I've considered lots of things, mainly about conserving the alternator and batteries and have decided to swap the existing immersion heater for a 500 watt one, 21 amp load instead of 42. Surecal mention them as an option, so I've emailed them. The panels view about this lighter load will be most welcome. Why is electrickery so bloody difficult to grasp? That is not an invitation for the obvious joke..... Oh go on then...

I have only had my own boats for about 10 years, and in early part of that time made many assumptions regarding batteries and power consumption. - Mostly trying to get 'blood out of a stone' - and it simply doesn't work.
Here is a short 'history' of my experience, and the conclusion I have evolved to that actually works for me.
On both boats I have had wet heating (Eberspacher on the first boat Mikuni on my current one) - So I have always been able to heat my water from those without the need for an immersion or running the engines - and for me I would not have it any other way - I use small radiators, so electrical power when running is minimal for the small water pump.
My first boat had an electrolux absorption fridge - an absolute disaster for running off batteries without the engine running although I actually had slightly more success when running it from an inverter on 230v because the thermostat works on 230v - But trying to keep up with the battery charging was still a nightmare.
My current boat is 24v and I use a domestic fridge via an inverter. I also run an engel fridge/freezer coolbox (beer fridge - my wife insists on putting food in the other one) again on mains via the inverter.
I started with a new battery setup (4x108ah) being charged from two engines via diode splitters. - This 'appeared' to work well, but I would occasionally get the inverter dropping out due to low voltage on the second/third day while off shore power. - I needed more help keeping tabs on the battery consumption so installed a NASA battery monitor - I find this a tremendous help in knowing how much power I have consumed, and how long I need to charge the batteries for.
But, I realised I needed to charge the batteries either for longer, or faster to keep up with my consumption.
I also changed twelve 20w halogen downlighters for 2.6w warm white LED bulbs - this saves a lot at the start and end of the season, and I don't worry so much about using lights now!
I next invested in a Sterling alternator to battery charger - this works just like a three stage mains charger, but directly from the alternators - and I can connect both the alternators to it for shared load. This works very well, but by now my heavy use of the batteries (regularly discharging to 50% capacity) was taking it's toll, and capacity was down to around 50% - so my battery bank would only last one night away from shore power.
It was time to dig deep, and I bought 4 250ah Elecsol AGM batteries - based on the fact that although they are affected by deep discharge, they are not nearly affected as much as normal lead acid batteries. - at 50% discharge they are rated for 2,500 cycles, and even to 100% discharge they can handle 1,200 cycles. - Oh yes, and they have a 7 year warranty, but looking at some of the posts here about warranties I will not hold my breath .
It was a big outlay, but € per AH, was no more expensive that my last 'marine deep cycle' batteries.
Over the last two long weekends I never discharged my batteries more than 30% even with minimal engine hours. Even so, that is a max discharge of around 150AH which would not be practical with 4X110 AH batteries as it would be around a 70% discharge.
I now feel confident enough not to take my generator away even on extended trips.

Sorry for the long post, but it may help you find the end of the road a little quicker (and more cheaply) than I did.

 

[Bosun Higgs]

The load is from a 1KW immersion heater (at 230 volts) so the (approx) 40 amp load is about right for 24 volts.

I've considered lots of things, mainly about conserving the alternator and batteries and have decided to swap the existing immersion heater for a 500 watt one, 21 amp load instead of 42. Surecal mention them as an option, so I've emailed them. The panels view about this lighter load will be most welcome. Why is electrickery so bloody difficult to grasp? That is not an invitation for the obvious joke..... Oh go on then...

It isnt difficult but if you read all the above posts you will get confused. Just read this one instead!

1/ The niminal ratings are just that - nominal. So your alternator wont deliver precisely 56.00000 etc amps. There will be a tolerance as there will be on the ammeter readings , on the immersion heater etc. So take all numbers as being broad brush.
2/ Your 1kw immersion heater will take about 45 amps at 24 volts allowing for inefficiencies in the inverter
3/ If the 30 amps output of the alternator is measured between the alternator and the battery bank, then the difference between alternator output of 30 amps and immersion heater input of 45 amps is coming from the only place it can - the battery banks.
4/ If you look at it, the alternator has a fan on the front. Thats because the alternator is not 100% efficient and more energy is going into it via the drive belt from the engine than is coming out as amps. That wasted energy appears as heat
5/ What is too hot? No one can answer that other than the alternator designer and in any case you probably havent got a thermometer with which to measure the temperature. You need to keep the alternator as cool as you can by making sure it has an air flow but that apart there really isnt anything you can do.
6/ Suggest you give it a good run. If it gets to the point of paint burning off it, switch off and send it back to the supplier as faulty. If it stabilises as most likely it will, you will gradually have confidence.


5/

 

[stuhaynes]

You have not mentioend the revs of the engine when you are doing this. Remember the 65A rating is the maximum output of the alt at IT'S rated shaft revs, which are subject to the ratio of the pullys on the engine crank and alt shafts.

As a separate matter, Balmar set their regulators to limit the Alt output when the temp gets to 110-115C as sensed by their thermistors attached to the alternator frame. It is 'B' hot and could perhaps boil water but I have also seen others suggest that 120C is OK. So much depends upon the airflow available in the engine compartment and/or if the alt has a fan which is part of the pully side arrangement.

Our cruising revs are 1500 - 1600 RPM. The drive pulley runs at engine speed. The drive pulley diameter was increased to 150mm when the new alternator was fitted. The alternator has a 50mm pulley. Based on all this, at cruising speed we should see the alternator doing 4500 RPM+

The alternator has its own fan and we opened the engine hatch at the alternator end to ensure good circulation.

It occurred to us that the leisure batteries were possibly not fully charged, which might explain why we were supporting a 40 amp+ load and the ammeter was registering a 30 amp charge! Does this mean we were asking the alternator to kick out 70+ amps? I'm very confused about this.

We've decided to fit a 500 watt immersion heater (if we can find one), this should halve the load on the alternator and hopefully reduce the working temperature.

Thanks everyone for your answers so far, Stu

 

[stuhaynes]

It isnt difficult but if you read all the above posts you will get confused. Just read this one instead!

1/ The niminal ratings are just that - nominal. So your alternator wont deliver precisely 56.00000 etc amps. There will be a tolerance as there will be on the ammeter readings , on the immersion heater etc. So take all numbers as being broad brush.
2/ Your 1kw immersion heater will take about 45 amps at 24 volts allowing for inefficiencies in the inverter
3/ If the 30 amps output of the alternator is measured between the alternator and the battery bank, then the difference between alternator output of 30 amps and immersion heater input of 45 amps is coming from the only place it can - the battery banks.
4/ If you look at it, the alternator has a fan on the front. Thats because the alternator is not 100% efficient and more energy is going into it via the drive belt from the engine than is coming out as amps. That wasted energy appears as heat
5/ What is too hot? No one can answer that other than the alternator designer and in any case you probably havent got a thermometer with which to measure the temperature. You need to keep the alternator as cool as you can by making sure it has an air flow but that apart there really isnt anything you can do.
6/ Suggest you give it a good run. If it gets to the point of paint burning off it, switch off and send it back to the supplier as faulty. If it stabilises as most likely it will, you will gradually have confidence.


5/

Missed this post, thanks for taking the time to be concise. If we can find a 500 watt immersion element I'll only have to worry half as much! I'm on the case.....

 

[Bosun Higgs]

If we can find a 500 watt immersion element I'll only have to worry half as much! I'm on the case.....

Ah, but for twice as long a time!

TBH I doubt you will find the smaller element makes much if any difference to alternator temperature

 

[DownWest]

Just a thought, but most alternators are based on auto units, which are not designed to run at full amps for long. Just for the time to get the amps used in starting the donk. Expecting them to run at full rated power will produce mucho heat, even with the not-very-efficient cooling fan. Bit like starter motors. Huge grunt, but only for short periods. 10secs recommended to stop over heating.
A

 

[BGW]

Our cruising revs are 1500 - 1600 RPM. The drive pulley runs at engine speed. The drive pulley diameter was increased to 150mm when the new alternator was fitted. The alternator has a 50mm pulley. Based on all this, at cruising speed we should see the alternator doing 4500 RPM+

The alternator has its own fan and we opened the engine hatch at the alternator end to ensure good circulation.

It occurred to us that the leisure batteries were possibly not fully charged, which might explain why we were supporting a 40 amp+ load and the ammeter was registering a 30 amp charge! Does this mean we were asking the alternator to kick out 70+ amps? I'm very confused about this.

We've decided to fit a 500 watt immersion heater (if we can find one), this should halve the load on the alternator and hopefully reduce the working temperature.

Thanks everyone for your answers so far, Stu

Do you have any means of 'smart' charging attached to the alternator? - If not, I simply cannot see how you would get anywhere near the rated output of your alternator for more than a few minutes, let alone more than that value.
Unless you have some odd wiring, the charge shown on the ammeter should be the amount of power being delivered - 30 Amps - How can the alternator be supplying the inverter without going through the batteries, and therefore the charging circuit and the ammeter?
My old batteries (4X108ah) would only accept a maximum of a 30ah charge - my new set (4X250) accept up to 40AH from the same setup. - I expect your batteries are limiting what you see on the ammeter, and with a 40AH draw from the inverter you are depleting the batteries.
At the end of the day, unless you get someone to check exactly what is happening with the correct equipment, we are all just guessing.

 

[Bosun Higgs]

Unless you have some odd wiring, the charge shown on the ammeter should be the amount of power being delivered - 30 Amps - How can the alternator be supplying the inverter without going through the batteries, and therefore the charging circuit and the ammeter?
My old batteries (4X108ah) would only accept a maximum of a 30ah charge - my new set (4X250) accept up to 40AH from the same setup. - I expect your batteries are limiting what you see on the ammeter, and with a 40AH draw from the inverter you are depleting the batteries.

Sorry but that's technical nonsense. The alternator and the batteries are in parallel. In a simple alternator plus batteries only system, current flows out of the alternator and into the batteries because the voltage at the alternator is higher than that of the batteries. As long as there is a voltage difference, current will continue to flow and that will not be limited in the way you describe by the batteries. Sure if you have too high a voltage and therefore too high a current the batteries will gas and boil and maybe even explode but the current they take in normal use is a direct function of the voltage difference and the resistance of the circuit. Incidentally the max charging current is usually recommended at something between battery capacity /8 and /4 ie 125 to 250 amps for your set up.

Nor does the current flow out of the alternator into the batteries and then into the inverter. The batteries and alternator are in parallel not in series. As the inverter takes current, the current in the system flows initially from the alternator which is at a higher voltage than the batteries ( it has to be to charge the batteries) but as the current builds up and the alternator voltage drops we get to a point where current starts to be drawn from the batteries. OK thats simplifying the system because there are all sorts of issues of the wiring resistances and things like battery internal resistance, alternator voltage regulator etc, which will determine the precise balance of current flows in the system but thats the basic idea.

 

[gus]

Cooling suggestion

If I may address the heat of the alternator and the requirement of cooling. Like you, I found my alternator was quite hot and was advised that normally on a vehicle there would be plenty of air circulating to keep it cool. In a boat, in an enclosed atmosphere there is not the same airflow. The fan blades on the alternator will pull air through the workings and the trick was to supply extra cool air. I subsequently fixed up some 4" foil ducting from one of the engine room air vents to the back of the alternator which allowed the alternator to run much cooler.