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I just upgraded my alternator on my 120 HP Lehman to a 150 amp ZENA alternator and a Balmar 612 smart regulator. I spent about 1/2 a BU total.

I just got back from 16 days in the Bahamas and a the solution was great. One thing I like about the ZENA alternator is high output at all RPM ranges. I can get 60+ amps at idle when leaving a harbor. I found out that in about 3 hours of moving I could recharge my 6 golf carts. I do not have a charger for my start bank, the genset does have a small (5-10 amp) alternator that keeps the start battery charged. You may want to consider putting a switch on one of the smaller alternators so you can enable it as a backup if your main alternator fails. I am personally against try to make two small alternator perform as one larger charging source (IMHO).

One thing I like about the ZENA alternator is that I can get 150 amps without a double pulley, and the frame size allowed me to use the existing mountings.

R. Smith
Edgewater, Florida

I'm unaccustomed to having any vendor remember a problem from weeks or months ago and tell me when it was fixed in production. You are truly unusual and superior.

I've installed studs (I'm not sure if that is the right name - but they are sort of long nuts), on one alternator with some washers for cooling. The lugs and wire remain warm, but not at all hot, to the touch and the unit works flawlessly. I'm inclined to leave it alone as-is since that circumvents the problem.

The other alternator was installed before I found a source of the studs, so it was just carefully installed. It also works flawlessly, but the wire and lug get hot - I can touch it but it is like a hot coffee cup. I gently tried to remove the nuts and install the 5/16" studs - but couldn't do it without turning the lug that goes into the alternator - I was afraid of internal damage so I stopped.

I'm out cruising now - but will return to S. Florida for a month or so during that time - and I'll send the alternator without the studs back for upgrade to the longer Silicon Bronze terminals. I checked - and while they aren't as strong as copper - Silicon Bronze conducts electricity about the same and has a lower coefficient of heat expansion (depending on the alloy), so overall they are probably better than copper for this application.

When I installed the studs, I put a very tiny quantity of conductive paste on the threads. No signs have emerged of the stuff dripping - and I test loosened the studs after a month and they have not corroded onto the threaded studs that produce from the alternator.

I agree with your consultant on the potential excessive heating caused by the AGM batteries. Also, I had to "depitch" the props with the AGM batteries and Zena alternators because when the units first start charging the load on the engine from the combined battery and alternators is more than the engine can produce - causing the engine to stall - a terrible thing to do to a diesel engine. I intend to reduce the maximum charging rate by reducing the excitation voltage from the regulator to the alternator - once my new prop is installed.

In the meantime, the maximum recorded output from the ZENA alternators is about 135 amps when only is running and a total of about 220 amps with both running into partially discharged batteries and no load. When running at full load (the house draws about 250 amps maximum), I produce about 180 amps from each Zena -- and heating becomes a problem.

I have upgraded one (of 4) cooling fans - am satisfied that cools the engine compartment and will upgrade the other three - producing about 350 cu. ft./min over the engine/alternator. There are no signs of heating damage at this point.

While my 900 AH bank of AGMs is large - it is really 2 banks of 450 Ah each split by about 40 feet of wire (round trip). So, even with "00" wire, the far away half of the batteries is not a major contributor to the load on the alternator (maybe 40 to 50 amps peak). Hard to visualize, but it seems to work OK

By the way, for a great story about you and ZENA alternators, check our shearwater-sailing website (CLICK HERE).

Stu Bell


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