35A alternator- Upgrade to 55A or 90A alternator?

[TQA]

If you are using a standard automotive regulator you need to replace it with a 'smart' one.

Look for something that has at least three stages of charge AND a battery temp sensor.

I have a Balmar Max Charge but there are other makes.

 

[ianj99]

I hear what you are saying, but as I don't have high-load items such as an inverter or thruster, and windlass is supplied by engine battery only when the engine is running, maybe it is unlikely the charge current will ever exceed around 50A, and the new cable only being rated at 70A is obviously not an ideal situation to have, but I could reviewed the situation once the 50% discharge alternator charge rates have been established, and should the need arise I could change it then.

One thing I did wonder about was, if I had to put bigger rated cable in for the alternator, could I disregard the present direct alternator charge wire from alternator to battery , and use some left over 50mm2 from alternator to the engine battery side of the engine battery isolator. This would be a permanent link using the engine start supply cable as the alternator charge feed to engine battery. This would be a quite short distance and maybe solve the problem.

This wouldn’t cause any issues would it? - Disregard that idea as it would mean that alternator current would be protected by a250A engine start fuse, not a good idea!

None of this matters unless you are happy running the engine for at least 5 hours at a time.

(Assumed 330ah battery bank, charging from 40% to 85% needs about 200ah (allowing for the fact that charging is not 100% efficient) at 40amps = 5hours (from a 55amp minimum ideally 70amp alternator). To get closer to 100% will need many more hours.
You could speed charging up with a digital regulator and even larger alternator assuming the batteries could stand the high charging current.

 

[pvb]

...just how he's going to get 50 amps out of a 35 amp alternator puzzles me.

Do try to keep up at the back! He was asking about installing a 90A alternator.

 

[pvb]

If you are using a standard automotive regulator you need to replace it with a 'smart' one.

If the standard alternator is delivering 14.6v, there'll be very little improvement with a "smart" regulator.

 

[xeitosaphil]

If the standard alternator is delivering 14.6v, there'll be very little improvement with a "smart" regulator.

Having read the post replies back again, is it considered normal then if the constant current of 4.5A doesn't reduce and is considered to be float charge as suggested earlier in the threads.
This is what I was concerned about -the fact it could cook the batteries if it was allowed to continue.

I think that I will remove it and get it checked out, just for peace of mind.

One of the reasons for buying a new one was to have the assurance that all was working as it should and the backup of the guarantee, and the other reason was I thought that the original 35A wasn't really up to the 220A battery bank, and didn't allow for any further upgrades of batteries that might need to be charged.


If I do decide to go for a new alternator, I think that maybe a 70A alternator would be a good upgrade, but with the price of a 90A at such a good price the fact it may not be working to its rated capacity is something I can live with, and it certainly would not be overworked so should last a considerable amount of time.

 

[Plevier]

Float charge is not a valid concept for an engine driven alternator that only runs for a few hours. It's a cyclic discharge/recharge system.
Float means days rather than hours.
Nonetheless 14.6V is high for this, as I said before it's normally in the range 13.8-14.2V.
Maybe your alternator has temperature compensation and is upping its voltage in present conditions.
It's unlikely to cause problems unless you are motoring a hell of a lot.
At 13.8V the current when fully charged would typically be 0.5-1A with your 220Ah capacity.

 

[xeitosaphil]

Float charge is not a valid concept for an engine driven alternator that only runs for a few hours. It's a cyclic discharge/recharge system.
Float means days rather than hours.
Nonetheless 14.6V is high for this, as I said before it's normally in the range 13.8-14.2V.
Maybe your alternator has temperature compensation and is upping its voltage in present conditions.
It's unlikely to cause problems unless you are motoring a hell of a lot.
At 13.8V the current when fully charged would typically be 0.5-1A with your 220Ah capacity.

Thanks Troubadour for that information that is very re assuring, will have to check things out now, get it removed and get it tested. Unfortunately I will be away over the Easter holidays so it will have to wait till my return.

Thanks to everybody for your contributions to this thread, it has been most helpful.

 

[Plevier]

Adding a bit more detail it rather depends on battery type too.
13.8V was appropriate for batteries with a medium sort of antimony content in the grid alloy say 3-5%.
Later the trend in europe was to about 1.5% antimony and you can put the voltage up a bit as it gasses less, so there was a drift to 14V or 14.2V.
Now more and more people are using lead calcium - American practise - which is more tolerant again of a higher voltage. Virtually all the "leisure" batteries now seem to be lead calcium.
Manufacturers like lead calcium because it enables them to offer "maintenance free" with more confidence, calcium is a much less unpleasant less toxic material than antimony for pollution control on manufacturing and lead calcium batteries have longer shelf life because of lower self discharge.
Downside is calcium is not as good as antimony for cycling or for high temperature tolerance (don't believe the advertising!)
If you look at serious cycling batteries such as Trojan T-105 they tend still to be lead antimony, up to maybe 7%. Hence the higher float current, higher self discharge rate and higher gassing when fast charged.
Above all relates to wet batteries, other considerations for VRLA, different topic!