Alternator question

[gonesailing13]

Looking to replace the alternator on my engine. My house bank is four Trojan 105’s wired as 12v. Also have a 12v start battery. Not knowing much on charging systems my question is how many amp alternator do I need. No need to charge at a fast rate but something that will work on five or more hours of cruising.

 

[C lectric]

Re the alternator, What do you have now and the mfgr.?

 

[gonesailing13]

Re the alternator, What do you have now and the mfgr.?

Right now I have a ( 90 amp, not sure the tags are worn off ) Prestolite. It has a date of 1995

 

[twistedtree]

Is the existing alternator going bad? 90A doesn't sound bad for the use your describe.

 

[DavidM]

Most OEM alternators are internally regulated. As a result they don’t charge the last 20% or so very fast.

Your four Trojans wired in series/parallel result in 440 amp hours at 12V. Lead acid batteries can be charged at up to 25% of capacity or 110 amps in your case.

A 100A Balmar high output alternator with Balmar’s external regulator should work very well in your situation.

Wire it through a Blue Seas ACR to the house and starting batteries to isolate them.

Or if your existing system works ok for you, stick with it, but do add the ACR, to protect the batteries from both discharging.

David

 

[High Wire]

90 amp alternator should serve you well. Only needs a single V belt and are readily available at a reasonable price. Make sure you match up the mounting system to what you currently have. That will make the swap painless as possible.

 

[twistedtree]

Most OEM alternators are internally regulated. As a result they don’t charge the last 20% or so very fast.

Your four Trojans wired in series/parallel result in 440 amp hours at 12V. Lead acid batteries can be charged at up to 25% of capacity or 110 amps in your case.

A 100A Balmar high output alternator with Balmar’s external regulator should work very well in your situation.

Wire it through a Blue Seas ACR to the house and starting batteries to isolate them.

Or if your existing system works ok for you, stick with it, but do add the ACR, to protect the batteries from both discharging.

David

I like adding an external regulator, but can it be done with the existing alternator?

 

[DavidM]

An external regulator could be hooked up to your OEM alternator, but I wouldn’t do it. Most auto electrical shops can add terminals for an external regulator. But you will then probably be putting a heavy load on it that it is not designed to handle.

Balmar alternators have heavier windings and diodes as well as a cooling fan that pushes more air, so it is able to operate at higher loads.

Even so, I would also buy the alternator temperature sensor that cuts back on output when the alternator temperature gets too high.

David

 

[TBill36]

My experience is with Leece Neville 90 amp internally regulated alternators. Pretty sure very similar to Prestolite. When I pulled the 4 T105 bank down overnight and trying to recharge running the next day, the alternator cooked itself. They are designed to put out 90 amps for about 20 minutes. Ask much more of it and it will overheat and cook the windings.

 

[twistedtree]

My experience is with Leece Neville 90 amp internally regulated alternators. Pretty sure very similar to Prestolite. When I pulled the 4 T105 bank down overnight and trying to recharge running the next day, the alternator cooked itself. They are designed to put out 90 amps for about 20 minutes. Ask much more of it and it will overheat and cook the windings.

And that's why the temp sensor is so important.

 

[READY]

If looking down the road do you anticipate adding lithium or doing extended anchoring. If so you may want to plan for that with your upgrade. I second the Balmar with their external regulator and temp sensor. Fairly simple install. But if you go to a higher output (generally >90 amps I think) you will need to move away from just a single v belt.

 

[Davil1]

Marine How has a write-up on this subject.
In my previous boat replaced the original Yanmar alternator ( 50 amps) with a Balmar high output and was very happy with it, but at the time was cruising and needed the extra charging in less engine running time.

In my current boat, no longer doing extended cruising my needs are more limited and after considering replacing my original Westerbeke alternator, on reading Marine How decided the hassle was not worth it.

Instead, installed a "Smart" external charger/regulator that tricks the engine original alternator, I am quite satisfied as puts out a higher output while using the engine (sailboat).lets me charge the starter battery first quite fast, and once charged diverts the output to the house batteries.
A thought.

 

[O C Diver]

Leece Neville has been owned by Prestolite for quite a few years. Balmar doesn't make alternators, they're made by others manufacturers. The 200+ amp versions are or were made by Leece Neville.

If you plan to use an external regulator, consult a alternator rebuild shop on suitability. Most regulators aren't designed for continuous output at rated amperage. This is why many external regulators have temperature probes to reduce the output when the alternator gets too hot.

There are also commercial grade alternators that are continuous duty at rated output. I put a 220 amp Leece Neville commercial alternator on my engine for charging the house bank. This is an album with the pics:

Albums created by O C Diver

www.trawlerforum.com

Ted

 

[Jeff F]

An external regulator could be hooked up to your OEM alternator, but I wouldn’t do it. Most auto electrical shops can add terminals for an external regulator. But you will then probably be putting a heavy load on it that it is not designed to handle.

Balmar alternators have heavier windings and diodes as well as a cooling fan that pushes more air, so it is able to operate at higher loads.

Even so, I would also buy the alternator temperature sensor that cuts back on output when the alternator temperature gets too high.

David

I think with a temperature sensor and external regulator there is no reason not to use the OEM alternator as long as you're not expecting rated output.

Adding better regulation is never a negative IMO. If alternator life is a concern you can set a conservative temperature limit and accept the reduced output. Your alternator will thank you.

That said, the last couple of times I've converted to external regulation I've also swapped to a Balmar alternator at the same time, mostly because the package pricing makes it a small incremental cost.

 

[READY]

For warranty purposes I felt better about the alternator/regulator kit from Balmar. I was pleasantly surprises to find that an internal regulator is present so if the Balmar external smart regulator failed it is very simple to use the internal one. The details can be found in the Balmar installation manual. I purchased an XT-170 but don't know if this is on other models. My Ford Lehman already had the dual pulley installed somewhere during its 48 year history so it wasn't a lot of work.