Charging on 24v Dynamo is wrong - ideas?

[Kvitstein]

Hi,

I have a 24v Leece neville dynamo that only puts out 26v at 500-650rpm (engine speed), and 28v at 900rpm+. This means she is not charging at low rpm which is a problem as this is a fishing vessel.

The dynamo has been taken out and tested, and found to be "ok". The person doing this indicated that it was likely that my batteries were dodgy, and dragging down the dynamos output. I however am not sure I buy that explanation. Most often its the dynamo thats naff dragging the batteries graudally down.

Does anyone here have an idea what the problem is? Does anyone buy the idea that changing batteries will suddenly increase charging voltage on my dynamo or wil these new batteries graudally be dragged down also?

Regards,

Kevin

 

[andyball]

we'd need to know the dynamo specs to know if that's wrong, or not.

I have a 12V and 24V alternator, and the 24 starts charging at almost double the engine speed of the 12V one - but there's nothing wrong with it.... the 24V model specs show that it's cutting in at the correct alternator rpm - which happens to be near twice that of the 12V.


I'd be happy if my 24V system charged at the same rpm's as yours - though I understand your problem with it.

 

[mainshiptom]

Dynmo's are known for bad performence in low revs this is why most people have switchd to aletrnators.

Tom

 

[Kvitstein]

Hi,

Think I might be confusing dynamo and alaternator. Mine is an alternator. Its no good that it starts charging at higher revs, as I use this engien a lot at low revs with electricity use...

Any suggestions?

Kevin

 

[spannerman]

Hi 'Whitestone' and welcome to the forum, I am based in Stavanger and work in the boat business.
If your alternator has been declared OK, then the problem is the low speed, its running basically at idle speed. It should charge at that speed but many alternators need to be run up to about 1500 rpm to wake them up and start charging, Volvos are well known for this. What you could do is fit a smaller pulley to the alternator which will increase its speed in relation to the engine and get you into the charging rev band.

 

[alb40]

Get the alternator tested at your local auto electrical sellers.

If it comes back as ok, then fit either a bigger pulley to the engine, or a small pulley on the alternator. This will increase its turning speed, and therefore charge at low engine rpms

 

[andyball]

The only solution - assuming that your alternator is behaving as the manufacturer intended ( check the specs) is to fit a smaller pulley on the alternator, thus increasing it's speed for the same engine revs. Or buy another alternator that does start charging at a lower rpm.

I found that 24V ones which begin charging at (alternator speed) 700rpm were rather expensive ( £300+, so I live with it.


Any good electrical/alternator supplier should be able to check the specs for your leece-neville and tell you if there's something better available.

to calculate alternator speed vs engine speed, you'll need to measure the sizes of the altern pulley and engine pulley.

 

[Kvitstein]

Hi Folks,

Good input - thanks. I have also written this on a Norwegian site and get similar replies, that i should change the discs that the pulleys run on to increase gearing. However, the disc on the dynamo is as small as it can be, and the disc on the engine is as large as it can be withhout the belt touching the bottom of the heat exchanger. So changing discs etc is not going to happen.

I might have to start looking at a new dynamo alltogether, but shall get teh specifications and contact leece Nevile directly to see if she is behaving as she should.

Its all rather irritating. Just as well I have seperate dynamo for the start batteries which works fine at this RPM.

Kevin