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moiuk

How hard can I drive my 95A alternator ?

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I have a 95A alternator on my Beta 43 engine and looking at a Lithium install so it will pull pretty much the full amount of current that I configure it to from the alternator.

 

I would like to pull as much current from it as possible to recharge the batteries and reduce the amount of time I need the engine running, but also want to not destroy the alternator in the process.

 

If I set it to pull 80 Amps for a constant 2 hours each day - would this be too much ? How would I know?

 

I can play with the current draw to test it out, but how will I know if the alternator is working too hard and will get damaged?  Is it as simple as how hot it gets? or are there other factors?

 

Any expert opinion to help me get this bit of my electrics right ?

 

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The first question to ask you in return is:-

What sort of belt is ion the alternator at the moment-

Vee (V-section) or,

Poly V - flat

 

 

If it's a small pulley - as is usual to get the alternator spinning fast enough to generate any current, then whatever belt is going to get quite warm and not wear very well.

A poly-V will work better.

Early 43's used V-belts, that was in the days when folks electrical demands were smaller...

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8 minutes ago, OldGoat said:

The first question to ask you in return is:-

What sort of belt is ion the alternator at the moment-

Vee (V-section) or,

Poly V - flat

 

 

If it's a small pulley - as is usual to get the alternator spinning fast enough to generate any current, then whatever belt is going to get quite warm and not wear very well.

A poly-V will work better.

Early 43's used V-belts, that was in the days when folks electrical demands were smaller...

I think it is a flat belt (I need to check when back at the boat tomorrow). Have attached a (bad) picture of it.

 

So - the main concern is the wear on the belt?

20190603_145109.jpg

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2 minutes ago, moiuk said:

I think it is a flat belt (I need to check when back at the boat tomorrow). Have attached a (bad) picture of it.

 

So - the main concern is the wear on the belt?

20190603_145109.jpg

That's a flat belt - so one objection removed.

However, there are more considerations which others may care to point out (for example - how well will your particular alternator cope with running at or near it's rated output for some time). I don't know, my kit is 24V and the alternators are designed for commercial vehicles - even so they get quite hot!                      

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I'm thinking of giving it a go at 80A and seeing how it copes, but trying to understand what signs I should look for if it's too much.. Of course if the belt snaps that's not a good sign, and if the alternator starts to smoke, also not good.  But hoping that there are more scientific approaches I could adopt to know I am pushing it too hard ?

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Measure its temperature with an infra red thermometer, over 130 s deg C on the outside is too much.

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26 minutes ago, hider said:

Measure its temperature with an infra red thermometer, over 130 s deg C on the outside is too much.

Remember there are 2 important factors for alternator temperature, firstly how hard it is working and secondly how will it is cooled.  So if you remove engine covers etc to measure the temp the cold air available to cool the alternator may be very different to when it is in normal running.  So best if you can fix a remote temp probe to the case of the alternator and monitor the temp with all covers in place.  Also the cooling will vary greatly with alternator speed as the effectiveness of the alternator fan is quite poor at idle, so again you should consider how to ensure no one ever charges at high load at low revs.

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2 hours ago, hider said:

Measure its temperature with an infra red thermometer, over 130 s deg C on the outside is too much.

Thanks for this - Have purchased an Infrared thermometer (looks like a great thing to have around regardless), and will try and figure out how to measure it without affecting the temperature too much (maybe I'll get a remorte temp probe too).

 

1 hour ago, Chewbacka said:

Remember there are 2 important factors for alternator temperature, firstly how hard it is working and secondly how will it is cooled.  So if you remove engine covers etc to measure the temp the cold air available to cool the alternator may be very different to when it is in normal running.  So best if you can fix a remote temp probe to the case of the alternator and monitor the temp with all covers in place.  Also the cooling will vary greatly with alternator speed as the effectiveness of the alternator fan is quite poor at idle, so again you should consider how to ensure no one ever charges at high load at low revs.

So if I am using the engine to charge (at 80A) whilst stopped, this is bad?  Will it perform better if I increase the revs whilst stationary? 

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22 minutes ago, moiuk said:

Will it perform better if I increase the revs whilst stationary? 

Yes, the cooling flow will be improved dramatically. 

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1 minute ago, WotEver said:

Yes, the cooling flow will be improved dramatically. 

If cooling is a major factor - seems logical to install a small fan down there pointed at the alternator if i wanted to drive it hard. (As an alternative to upgrading the whole alternator) ?   Any flaws with this ?

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6 minutes ago, moiuk said:

If cooling is a major factor - seems logical to install a small fan down there pointed at the alternator if i wanted to drive it hard. (As an alternative to upgrading the whole alternator) ?   Any flaws with this ?

No flaws at all, it was going to be my next suggestion. Note that alternator fans pull the air through from the back to the front, so consider that when placing the fan. 

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But without  engine space vent, preferably 2  in and out, the hot air will just be recirculated even if you have umpteen fans going. Worse if its a metal deck in a heatwave with the sun beating on it.

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24 minutes ago, moiuk said:

If cooling is a major factor - seems logical to install a small fan down there pointed at the alternator if i wanted to drive it hard. (As an alternative to upgrading the whole alternator) ?   Any flaws with this ?

To cool the alternator you need cool air, so a fan blowing cool air from (for example) outside the engine hole on to the alternator will help greatly to cool the alternator whereas a fan drawing air from over the engine exhaust will act as a fan heater and may make things worse.  These things are more complex than they first appear.

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4 minutes ago, bizzard said:

But without  engine space vent, preferably 2  in and out, the hot air will just be recirculated even if you have umpteen fans going. Worse if its a metal deck in a heatwave with the sun beating on it.

Fortunately, in my case I should only need to drive the alternator hard when it is cold.  I am expecting that my solar panels will give me all the charging I need during hot and sunny days, and it will be winter when I will need the alternator to do it's best for me..

 

4 minutes ago, Chewbacka said:

To cool the alternator you need cool air, so a fan blowing cool air from (for example) outside the engine hole on to the alternator will help greatly to cool the alternator whereas a fan drawing air from over the engine exhaust will act as a fan heater and may make things worse.  These things are more complex than they first appear.

Point taken, my engine bay has some good circulation,  so I'll position the fan(s) accordingly and take some temperature measurements.

 

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1 hour ago, moiuk said:

Have purchased an Infrared thermometer (looks like a great thing to have around regardless),

They frequently are...

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4 hours ago, Chewbacka said:

 Also the cooling will vary greatly with alternator speed as the effectiveness of the alternator fan is quite poor at idle, so again you should consider how to ensure no one ever charges at high load at low revs.

 

I'm confused on this point. Do some alternators allow variable charging at given revs? My alternator output varies according to revs so at idling output is low.

2 hours ago, moiuk said:

 

So if I am using the engine to charge (at 80A) whilst stopped, this is bad?  Will it perform better if I increase the revs whilst stationary? 

 

I don't understand how you could be charging at close to the alternator's maximum output unless you increase revs?

Edited by blackrose

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6 minutes ago, blackrose said:

 

I'm confused on this point. Do some alternators allow variable charging at given revs? My alternator output varies according to revs so at idling output is low.

 

I don't understand how you could be charging at close to the alternator's maximum output unless you increase revs?

Im no expert,  but have noticed that when I pull a lot of current from the alternator, the engine works harder automatically.  You can hear it rev up even if the throttle is on idle.

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Ok, mine might increase revs slightly but not nearly enough to increase the alternator output close to its max.

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Regarding ventilation in the engine 'ole,  I fitted a "clam shell vent" in my deckboard and mounted a computer fan to cool the alternator. I think this helped because if you think about it, the engine itself draws a lot of air in just to run so it will draw in cold air, the clamshell vent just makes it easier.

Phil

Edited by Phil Ambrose

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The perceived wisdom is that you should NOT run the engine at idle to charge the batteries but run at around 1200 rpm.

You can't force the alternator to output more power to some extent that's governed by the rotational speed. If you know what make / model it is, to can find graphs on the internet.

(On my boat - where I have a charge controller, if I run at tickover, the belt slips to such an extent that I switch off the controller for a while until the initial current subsides.

 

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10 hours ago, blackrose said:

Ok, mine might increase revs slightly but not nearly enough to increase the alternator output close to its max.

Two things - Beta specifically warn against battery charging at idle speeds as the vibrations risk damaging the engine.  Also the alternator will not output it's max current at idle, but it will still try to output as much as it can if the load is high, and with a low speed the alternator may not adequately cool in a hot engine space.  Up the revs and you will not only increase the alternator speed (so it's own fan runs faster and gives much better cooling) but also the engine running faster will use a lot more air pulling more cool air into the engine space and so dropping the ambient temperature.  Of course an engine at high revs AND high load (such as going up river) will generate a lot of heat, but if just battery charging it will not use a lot more fuel, but will pull in cool air.

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10 hours ago, blackrose said:

I'm confused on this point. Do some alternators allow variable charging at given revs? 

 

Not as far as I know, in fact I'd go as far as to say none in the type of alternator normally fitted in narrowboats.

 

This point arose however on the OP's other thread about installing a proprietary Victron lithium battery bank, where the Victron lithium controller includes exactly this function, presumably to head off streams of 'busted alternator' failures from overheating.

 

The problem being that peak rated alternator current doesn't happen for long when charging LA batts. After a few mins at peak rated output battery voltage rises a little and charge current starts slowly and progressively dropping from peak, so the alternator needs progressively less cooling. With lithium however, full rated alternator current will be sucked out of the alternator for hours on end (until charging is interrupted or there is some sort of current limiting controller fitted), for which the alternator cooling is not designed to cope.

 

 

Edited by Mike the Boilerman

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4 hours ago, Mike the Boilerman said:

 

Not as far as I know, in fact I'd go as far as to say none in the type of alternator normally fitted in narrowboats.

 

This point arose however on the OP's other thread about installing a proprietary Victron lithium battery bank, where the Victron lithium controller includes exactly this function, presumably to head off streams of 'busted alternator' failures from overheating.

 

The problem being that peak rated alternator current doesn't happen for long when charging LA batts. After a few mins at peak rated output battery voltage rises a little and charge current starts slowly and progressively dropping from peak, so the alternator needs progressively less cooling. With lithium however, full rated alternator current will be sucked out of the alternator for hours on end (until charging is interrupted or there is some sort of current limiting controller fitted), for which the alternator cooling is not designed to cope.

 

 

A much  better summary of my issue that I am trying to manage, thanks Mike.

 

The victron bms allow me to 'set' the constant current being sucked out of the alternator,  and I want to maximise this to reduce the amount of time I have the engine running. The lithium are being install at the end of June so I will be able to report back what I find. 

 

As you say, the alterna6 is not designed to run a peak for extended periods, and yet this is exactly what I will be wanting it to do. I'll monitor the temperature and belts carefully and adjust the  current pull till I find something that works.

 

Will also adjust the throttle to get that to the correct place as well.

 

In case it is of interest, my alternative solution was to upgrade the battery charger and buy a generator. A 100Amp battery charger is for some reason very expensive and so the alternator solution seems to be the way to go. 

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Engines consume large volumes air and with only one vent the engine space won't be much cooler when the engines running.

   During the war:) when diesel electric submarines got the emergency and did the ''eneny in sight thing, Dive Dive Dive'' and the last man in secured the water tight lid from the conning tower and the engineers were  caught napping and slow to stop the engines, the whole interior of the boat would be put into an almost immediate terrible vacuum which affected the crew horribly. They would almost double in size and almost burst with eyes and tongues popping out and lots of vomiting until the engines were shut down when compressed air would be released to restore normal air pressure and everyone shrank back to normal again and eyes and tongues when back in.  The air intakes on the engines were as big as dustbins.   There was a severe punishment for the engine room chaps for being too slow but I can't remember what it was.

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18 hours ago, WotEver said:

Yes, the cooling flow will be improved dramatically. 

You will not get full current (or anywhere near it at idle speed), so you are unlikely to cook the alternator in this way. However more cooling would be good if you want the alternator to last

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