How hard can I drive my 95A alternator ?

[Dr Bob]

On 10/06/2019 at 09:43, Dr Bob said:

Now, this week, once the sun goes in today, we wont see it again until the weekend and I will experiment and go to the next battery setting so likely to start with 60A going in decaying with the heat to 50A. I will keep a close watch on the temps and report back. I think that will be pushing it. I doubt these 90A alternators can work at more than 50% output continuously.

Moiuk,

The lack of solar this week has meant I have been running the engine a bit more and with all the rain we are staying put.

Today then, parked up, I ran the engine for an hour with the box managing the power output of the alterator set at a higher power. If you remember I had been seeing 90°C in the centre of the alternator top and 50°C on the casing by the diodes with a 50A output dropping to mid 40'sA when hot at 1200revs.

Today I was seeing 95°C and 60°C with a power of 62A out dropping to circa 57A when hot. This dropped to 37A on tickover. The 'box' managing the power is a Sterling AtoB which switches off three times an hour for 3 mins (to charge the engine battery but this is disconnected) so the alternator drops to 15-20A for the 3 mins and the alternator cools from 95 to 80°C in the 3 mins.

I think I would be happy with this for an hour with cool ambient temps ....ie today.....so ok during the winter when you are not moving much....but I dont think I would like to keep this going for 3 hours or more. The rain has started down again this pm so I will likely run for another hour this afternoon to get a net 110Ahrs in today plus a bit of solar (maybe 10-20Ahrs).

I will limit my charging to 40-50A when boating and then 50-60A when parked and can keep the revs up.

Let me know if you do better than this when you get your system installed.

[moiuk]

On 09/06/2019 at 18:16, OldGoat said:

FWIW Beta build engine power plants to be be price competitive while satisfying what they thought would be the average demand for their perceived customer base (and looking at the OP's engine bay) - were not too space hungry.

IMHO what they have fitted to your '43  will not take kindly to running at peak power regularly - especially if it's been tweaked to go the extra mile.

What you need is a lorry / bus type unit.

If you can find out what was fitted (ask Beta very politely - with the engine number- what the unit and if you're lucky you'll find the standard power curves on the net. IIRC they used to fit ISKRA alternators - mid range kit....

I have emailed Beta and see if they can help with this - good idea

 

 

[moiuk]

Found the power curve chart for my alternator.

 

Need to do a few tests to see if this is what happens in real life.  I have bonded both my 95a alternator and 45a alternator to charge my battery bank and am getting 40amp from both at 1000rpm which confused me as I expected more from the 95a alternator. However this power chart seems to match this. I'll try increasing the rpm next and see if I can get more out of the 95a alternator. 

 

 

[Alan de Enfield]

21 minutes ago, moiuk said:

Found the power curve chart for my alternator.

 

Need to do a few tests to see if this is what happens in real life.  I have bonded both my 95a alternator and 45a alternator to charge my battery bank and am getting 40amp from both at 1000rpm which confused me as I expected more from the 95a alternator. However this power chart seems to match this. I'll try increasing the rpm next and see if I can get more out of the 95a alternator. 

 

 

 

Basically - unless you 'thrash' your alternator at 6000 rpm you get a fraction of the rated output.

With the 'normal' 3:1 pulley ratios it shows that you need to run your engine at 2000 rpm to get somewhere near the rated output.

 

 

These are 'actuals' on my two engines / alternators. Both alternators are 70 amp.

 

Port Engine / Alternator

1000 RPM = 28 Amps

800 RPM = 21 Amps

 

14.2 volts at Alternator

 

Starboard Engine / Alternator

1000 RPM = 30 Amps

800 RPM = 22.5 Amps

 

14.0 volts at Alternator

 

The output will also obviously depend on the state of charge of the batteries - it is them that control the charging current - NOT - the alternator.

 

 

My alternators have a cut-in speed of 1200rpm and a max speed of 15,000 rpm.

Edited June 29, 2019 by Alan de Enfield

[moiuk]

This is really helpful  my battery bank is lithium, so it will pull everything it can get from the alternators.

 

Just tested it at 2000rpm and getting 100amp total from both alternators which is what I was originally expecting. 

 

I have ordered a clamp meter so I can measure them separately.

Edited June 29, 2019 by moiuk

[WotEver]

2 minutes ago, moiuk said:

Just tested it at 2000rpm and getting 100amp from both alternators which is what I was originally expecting. 

Keep an eye on their temperatures. 

[moiuk]

4 minutes ago, WotEver said:

Keep an eye on their temperatures. 

Will do. I am a bit worried about the smaller 45a alternator.

 

 

[nb Innisfree]

Innisfree had a large frame Leece Neville alternator, 24v 100A. When it was cold and batteries were low it could generate the full 100A at approx 1200 RPM engine speed (2400 RPM alt speed) when it was hot and batts full w/m would pull the same 100A but would need 1800 to 2000 RPM engine speed to keep up, Gibbo reckoned it was because of heat.

 

Never did get around to installing a fan to supply cool exterior air. 

 

Single A section V belt struggled but when doubled up they coped very well.