Alternator Question

[sdemore]

OK guys, have another question for you. My original Motorola 37 amp alternator died. I took it in to the local alternator rebuild shop yesterday and they threw it up on the test jig. No output and the bearings sounded like hell. I asked how much to rebuild and the guy said it depended on what parts had to be replaced, but the replacement cost was $198, so it could be anything up to that.

I picked it up today and for $211 (with tax), I have a freshly painted, rebuilt, 37 amp alternator. The new regulator has an adjustment pot for output voltage.

Was that as dumb a repair as it feels? I could have bought a 55 amp for $20 more on the Moyer site? Is there an advantage to a lower output or keeping things original? The boat was designed for it and while I have added a GPS/depth sounder, I also went to LED lights, so it should be able to handle power needs.

I have a 2nd one sitting here that I was going to have rebuilt as a spare, but I don't think I want to do that now. I'm thinking buy a 55 amp for primary use and use this one as the spare.

What do you think?
Steve

[ndutton]

I think you answered your own question and I agree with your post-sortie analysis.

[JOHN COOKSON]

Is there an advantage to keeping things original?
Steve

IMO no.
A lot of new knowledge, products, procedures, upgrades, ect have come out over the years since the A4 was manufactured. The EI is a good example.

TRUE GRIT

[joe_db]

I hate to say this, but that was not a cost-effective repair
I didn't pay half that for my nice Balmar 65 amp alternator (http://www.moyermarineforum.com/foru...ghlight=balmar), you could have got a 50 amp unit for hardly any more money, and there are plenty of marinized 10si units on Fleabay for about half that as well.
Don't go paying $200 to fix the other one.
Speaking of alternators...Fleabay has more cheap Balmars going right now: https://www.ebay.com/itm/Balmar-81-5...RZ-OhU&vxp=mtr
That one is a 1" foot, so you will need a 1" spacer and a regulator to make it work.

[tenders]

I don't think it was SUCH a bad decision. The problem with the stock alternator is that it runs at a relatively low voltage and rarely put much of its capacity into the battery. An adjustable regulator is a good upgrade, allowing you to solve that. They may well have already adjusted it in the shop to solve it.

If you have LEDs and don't use a reefer or an inverter much on the hook, you may not really need more charging capacity. The bigger Balmar alternator is nice, but there's no need to beat yourself up over the difference between a $200 complete solution available at your convenience, and an $80 solution that will need some time and materials to get going.

I have a big alternator myself, but I'm on a mooring and use the inverter somewhat regularly. It was an opportunistic buy and required a trip to the alt shop...a good upgrade but not a turnkey solution.

[joe_db]

I have a 35(37?) and a 50 amp Motorola around my shed someplace. I used an external regulator to increase the charge voltage on them and it helped in the short term. Long term neither one of them stood up to the increased output, they would lose diodes one by one. When I had a local shop that would replace them cheap it was one thing, but they went out of business (from replacing diodes cheap maybe ) and that was no longer viable.

Don't beat yourself up, you have a working alternator now and did not before. It will be a great spare to have on hand if you get something else

[Administrator]

Hi, Steve:

How big is your battery bank(s)?

Bill

[tenders]

Hi, Steve:

How big is your battery bank(s)?

Bill

Yeah. That is a very key question. No need to be cutting cheese with a weapons-grade laser.

[edwardc]

Rule-of-thumb is that the alternator capacity, in amps, should be at least 25% of the battery bank capacity, in amp-hours. There's a good article on alternator capacity and charging requirements here:

http://stevedmarineconsulting.com/the-relationship-between-battery-bank-size-and-charge-capability/

[Marian Claire]

I have also read that there is a recommended max output based on battery bank size. That was my concern.

"Sizing the alternator

Your alternator should be sized appropriately to produce the highest amount of current your batteries can accept (their charge acceptance rate, which ranges from 25 to 40% of the battery bank’s total amp hour capacity). This gets the bank recharged as quickly as possible, minimizing the engine running time and the fuel needed to replenish the batteries. Thus, a boat with a 200Ah battery bank should be paired with an alternator that maxes-out at 50-80A."

Dan S/V Marian Claire

[joe_db]

That is assuming you have a really dumb regulator. Modern or even halfway modern regulators allow use of quite large alternators on smaller battery banks. Using the max capacity of the alternator itself to control charge rates is 1970s or older tech at best.
Also note the acceptance curves you get from battery manufacturers assumes an infinite current source
The C-208 I used to fly had a battery that was 28 AH and the generator was 200 amps!* This worked fine. It was set to 28 volts and the battery could not draw enough charge current at 28 volts to hurt itself. Kind of like for a boat you could hook up a 2,000 amp charger at 13.8 volts with no issue but one set to 15 volts would blow the place up. The ground power cart I drove around at BWI could supply 400 amps at 28 volts to the planes I connected it to and most of their batteries were about that size (28aH) too.

*yes it had a generator, not an alternator

_ EDIT
For one example, the ever popular 10si series alternators have all kinds of regulators available that range from perhaps lower than 13.8 on up through 14.8 and maybe beyond. A huge 120 amp 10si with a 13.8 volt regulator isn't going to overcharge anything, if anything it won't charge enough at that low setting.
If you don't want to cough up the $$$$ for a marine smart 3 stage regulator, Transpo makes a few regulators you can adjust yourself to the settings you want.

https://www.amazon.com/World-Power-Systems-Voltage-regulator/dp/B00OBTI5Q2/ref=sr_1_4?ie=UTF8&qid=1518726243&sr=8-4&keywords=transpo+regulator

This is one of them. You can search FleaBay and Amazon for Transpo regulator and find them. I use an older manually adjustable regulator and it was worked for 25 years as of now.

[sdemore]

Bill (and all),

I went to the boat today to install the alternator and see what the battery sizes were. Good news, the alternator was charging well. Couldn't leave it running because the raw water system is drained and I didn't want to drain it again.

Bad news, I forgot to look at the batteries. What I can tell you is that one is a deep discharge, probably 8 or 10 years old, that a friend donated from his boat (spare). I think it is big enough that it used to start his Mercruiser motor, but I don't know that it would any more. The 2nd battery is a standard lead acid borrowed from a spare car on blocks in my garage.

Both batteries are temporary, just to get through some of the winter projects (this is a complete project boat) and will be replaced this summer. I hope to be there again this weekend and will check them then.

[joe_db]

When you get your batteries sorted let us know. The charge settings that are great for one type will ruin another.

[sdemore]

OK, got to spend some time with the boat today and got the battery information.

This is temporary, as I will be replacing at least the automotive battery this year (have to put it back in the car!) and perhaps both of them.

Primary battery: Autocraft Marine deep cycle battery
Cold Cranking Amps @0 degrees - 550
Cranking amps @32 degrees - 685
Reserve Capacity - 140

2nd battery: Sears Diehard Automotive battery
Cold cranking amps @ 0 degrees - 690
Reserve capacity - 85

Steve

[tac]

Sadly, your battery information is incomplete. The two most important specs are the number of amp-hours (Ah - 90?, 110?, 120?), and the battery case size (Group Gr24? Gr 27?, Gr31?). Also the type of battery would be nice to know: flooded lead acid, sealed lead acid, AGM, or gel. The battery type differences aren’t minor. The optimal charging voltage can differ for each type.

If the case size is not shown on the battery, measure the height, width, and depth. That will give a rough idea of battery capacity in Ah. As for battery type, if the cell caps are removable (screw caps), it is likely flooded lead-acid. If not, see if any sticker says “AGM” or “Gel”.

To learn more about batteries and their charging and care, I suggest, before you buy new batteries, reading chapters 1 and 2 of Nigel Calder’s most excellent book, “Boatowner’s Mechanical and Electrical Manual”. After reading those two chapters I expect you’ll voraciously devour the rest of the book.

https://www.amazon.ca/Boatowners-Mechanical-Electrical-Manual-4/dp/0071790330

Like the Moyer A4 manual, Calder’s book is a must for any boat owner.