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What Our Alternator Customers Report:

Have bought five over the years for Marine use -- all are still working and I'm getting another... Great alternator!

M Salatino
Green Cove Springs, FL

This is Ray Cayer from RI, I bought several Zena alternators this summer. The last one was a 250 amp with external rectifier/diode assembly. Everyone was very impressed with that equipment. It worked great and the owners are very pleased. The other two were the 150 amp models and they are on large fishing boats performing well every day. I will be ordering two more of the 150's here very shortly.

I believe that the ZENA is the best alternator available and the most reasonably priced,  that is why I sell it.

I just upgraded my alternator on my 120 HP Lehman to a 150 amp ZENA alternator and a Balmar 612 smart regulator.

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

Stu Bell

John and Tony,

Let me presume to introduce you both. John has been my advisor and supplier of Balmar alternators and regulators since the Shearwater was commissioned in 2000. He has help me many times recover from many problems - most of my
own making - and supplied parts and batteries urgently to get me going again
when needed.

Tony supplied my current alternator, a Zena 200 amp welding "generator" that is installed in place of one of the Balmars. Tony also worked hard through the sales process to ensure I could fit the new alternator into my space and wiring. He worked especially hard when the oversize wire connected to the positive terminal partially parted causing it to heat and destroy the connector.

Currently, the Zena alternator is supplying all our power needs on about 2 engine hours/day of running time - putting out about 160 amps at about 2500 engine rpm. This is about 70 to 80 amps more than the Balmar delivered under the same conditions.

Additional, during the three+ years of Balmar ownership, I've paid for 3 rebuilds, one by Lestek (over $500, one by ASR, about $250, and one by a place in PR for about $200. That brings the 3-year cost of ownership (excluding shipping and aggravation) of the Balmar to about $2000. The Zena has cost just about $500 so far and has a 3 year warranty that would have covered the repairs I had done on the Balmar.

John, It might be worthwhile if you and Tony "talked" a bit about your representing Zena in Florida. It seems to be a better-built alternator - slightly easier to install (a 3" saddle mount), and has a superior warranty. You could save your clients $500+ on day one, provide what seems to be a superior product, and eliminate their year repair/rebuild costs (for high-hour users) with the Zena warranty.

All the best,
Stuart Bell

You may (or may not!) recall that I had correspondence with you in 2010 when I bought your alternator & welding gear- sent to Sydney, Australia.

I built up my generator/welder onto an aluminium frame and also incorporated my own sophisticated alternator regulator (for battery charging). It is driven from a Yanmar L100 single cylinder 10HP engine.

After a lot of testing, I shipped it to France and installed it on my 111 year old Dutch barge.

It has been working very successfully ever since. In the 6 month cruising season, I use it every few days for a couple of hours to fully charge the 1,000AH AGM  battery bank at around 180amps. (It will deliver 220amps but the engine struggles at that level so I run a bit lower.

I have used the welder far more than I expected with improvements, repairs etc and it is a delight to use. I have never needed maximum welding amps.

All the best,

David Kerr

A Typical Question and Answer:


I'm interested in your serpentine kit and a high output Alternator for a Volvo D2 55 is the same as the Perkins 404c 22 engine, it seems Volvo D2 55 serpentine belt kit and 200 amp high out put alternator will fit my Perkins engine as the pulleys are the same on both engines.

I have an external regulator Balmar Model MC 612.

Can you please send me product details model reference numbers and availability plus a quote for these Products.

I look forward to your reply,

John Majewski


Sorry, but we don't make pulley kits for marine engines. There is just not enough volume to make the tooling and/or R&D investment worth while. Amortizing such an investment over the number of individual kits for a particular alternator and for a particular engine would make the kit cost about as much as the engine.

We've, almost certainly, got the high amp marine alternator that you need -- and any of our units will work with your existing regulator -- but it will probably not be a bolt-in replacement for your existing unit.

And, frankly, pulleys are just part of a proper marine alternator retrofit/installation.

In most cases, particularly for people wanting to move up to charging/generating equipment far beyond the capability of the tiny alternators that come stock on marine engines, bracketing for physically large alternators becomes a necessity.

Therefore, we recommend that mechanical savvy owners of marine engines simply do a little bit of simple bracketing (or contract with a good marine or automotive fabricator) -- and install the size alternator that they need on their engine (not just one that's the same size as their existing model) -- using simply fabricated components and/or off the shelf parts.

For example, bracketing and drive pulleys for a 250 amp alternator will be different than those needed for a 150 amp model. And, given the variety in marine equipment needs, and the wide range of personal preferences in the world of boat owners. Fitting the right alternator is key to a satisfactory experience.

A bit of a "soap box" speech:

In our opinion, the "gold standard" for such installations often comprises a large heavy duty alternator installed secondary to the engine's small stock alternator -- with the stock alternator dedicated to the starting battery and underway electrical loads (instrumentation, etc.) and with the high amp alternator dedicated to a large house bank made up of deep cycle batteries. A step up from this is the installation of multiple high amp alternators fitted to the engine -- optimizing charging current, balancing he mechanical load of large alternators on the engine bearings, and providing superior performance on rather slow turning marine power plants.

It's too bad that boat manufacturers do not simply require engine manufacturers to fit the largest possible charging system that the engine chosen for the vessel can support, while also providing a large enough battery bank to allow that charging system become part of an efficient and cost effective means to replace on-board electrical generators.


Tony Blazina
ZENA, Incorporated

Hello Tony,

I'm very impressed with your reply, normally no one bother to reply, even though you do not have all what I need as a kit. I take your point on manufacturing affordability and lack of foresight by marine engine manufactures. More important your rare give advice seems as you say follow the gold standard of two Alternators, in my case I have a water maker high pressure pump to balance out the a High output Alternator if I can ever find a way to set it up problem free. The problem is matching all the components, like you say bracketing for physically large alternators, when sourced from different suppliers they never matches up.

I will take note of your emails valuable advise. 

John Majewski

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