13.2 kW Alternators and Beyond


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On Dirona, we aim to always run the boat using a single power source. When we are plugged into shore, we aim to drive the entire boat off of shore-side power and never run the generator. This may sound easy, but in Europe you frequently won’t find more than a 16A shore power service and we have been at marinas where only a 10A service was available. We have engineered the boat’s shore side power supply system to be able to run off two shore services, so we can easily operate the boat on dual 10A or even dual 8A. As I write this, we are plugged into dual 16A shore service at Amsterdam City Marina. The dryer is on, the reverse cycle heat is on and the boat is comfortable and warm and the generator will never need to run.

When under way, we again use only a single power source. Here we use the main engine and we don’t ever run the generator when underway. We do this by using two 4.5KW alternators for a combined available power of 9kW. When underway, it’s common for us to two have two HVAC units running and, even when we are using the dryer or the oven, all the power is supplied by the main engine. Again making this work sounds easy but it takes very large alternators to deliver this much power and not all alternator specifications are created equally.

If you are interested in more detail on the eventual power system we settled on for Dirona to achieve these goals, there is more data at: A More Flexible Power System For Dirona. The most important part of this design for what we are discussing here is the use of high-output alternators to allow the main engine to support the full hotel loads of the boat. The goal is to be able to rely on the excess power available from the main engine rather than needing to run an auxiliary generator when underway.

Our previous boat had two 105A small-frame Delco alternators at 12V for a combined total of 2.4kW. On that smaller and simpler boat, this was perfectly adequate and would support our average loads quite well. However, it turns out that the 105A rating was an output that the alternators “could” produce under ideal circumstances.  They can easily do this for 30 to 90 seconds, after which they produce absolutely no power and smell terrible :-). Through trial and error and discussions with Delco, we eventually learned these alternators can produce about 77A continuously. Generally, as long as the alternator never exceeded 225F, it would run for years without problem. They were quite capable of 105A but the temperature went up so quickly that they could really only safely produce 105A for a portion of a single minute before they again needed field winding and bearing replacement.

A big part of the problem is these alternators were designed to charge automotive start batteries that rarely discharge deeply and are of limited capacity, so don’t take long to charge.  They weren’t designed for continuous-duty applications.  And, at least a small part of the problem is the 105A specification is a bit optimistic in any application. The spec really is more of a marketing tool than application design guidance.

When we specified the current boat, we wanted a power system that could produce continuously and opted for the Balmar 97EHD-190-24 alternator with a Balmar MC624 external regulator. This alternator produces a legitimate 190A and only derates to about 177A when hot (it’s normal for alternator efficiency to go down slightly with temperature). Initially we set up the alternator regulator to limit the alternator temp to the 225F that we found through trial and error was the reasonable limit on our previous small-frame automotive alternators. We ran like this for 6 months before we lifted the maximum temperature to 250F. We ran like this for 2 years or around 1,563 engine hours.

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At this point, we decided to add a second alternator of the same specification as part of A More Flexible Power System For Dirona. At the same time, we decided to run an interesting but potentially expensive experiment. We were very interested in how hot these alternators could run without negatively impacting service life.  And, now that we had two alternators installed, we were willing to run the risk that one alternator would fail. We removed the temperature limits and both alternators often were right around 300F when operating near the equator and charging at full load.

We fully expected this experiment would eventually end in a failed alternator, but replacing field windings and bearings isn’t that expensive and we felt it would be extremely interesting to have real data and know exactly what was possible rather than rely on expert opinion. This experiment effectively never ended.

There is now 10,200 hours on the boat and both alternators continue to reliably produce the nearly 4.5kW that they did when new and neither has ever shown a fault.  Just getting 9 years and over 10,000 hours from an alternator between services is impressive. Getting that service lifetime while running at temperatures that often range between 275F and 310F is truly impressive. These alternators continue to operate flawlessly and we often run them at max output for hours at a time with temperatures in the 300F range. We’re very impressed with the Balmar 97EHD-190-24 and recommend them frequently.

As much as I love these alternators we’re always on the lookout for higher output options. Last month while attending METSTRADE 2018 in Amsterdam, we came across Dixie Electric and got very interested in their Delstar Series 400 alternators. These are absolute beasts, putting out an incredible 550A at 24V. That’s 13.2 kW from a single alternator.  Amazing! In fact it did seem a bit hard to believe, but the deeper we dove with the Dixie Electric folks, the more clear it was that they had considerable experience and fully understood what it takes to keep an alternator running under continuous duty in difficult environmental conditions. The first thing to look for is how are they getting the heat out?  Then is the system capable of withstanding the high localized heat loads that will be present at these output levels even with very well thought through cooling design? Is the drive system capable of delivering the required HP without belt slippage or alternator bearing overload? The more we asked, the more impressed we got with the Dixie Electric design.

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These look very strong but who wants to be the guinea pig for even a very good design team to learn about the difficulties of building high-output alternators? In getting into the details, Dixie has seen most failure modes, talks openly about what they did about it, and how the designs have changed to mitigate these fault modes. They point to their large fleet of over the road buses and trucks, their primary market, as proof they have produced a reliable product that can deliver high amperage continuously in even unfavorable environmental conditions. Large buses and even trucks have increasingly large hotel loads as more and more accessories are added (HVAC is often one of the biggest consumers), so this market segment continues to buy ever larger alternators.

The bus and truck segment is the same use case that drove the development of the base alternator design we are currently using. We’ve been extremely impressed with the Balmar 97EHD-190-24 that we are using, and the Dixie DelStar Series 400 looks like a very interesting product that more than doubles the already high output we are currently using. 13.2 kW from a single alternator is amazing. In fact, even if you chose to run conservatively and derate to 10 kW, it’s still an impressive amount of power from a single alternator.

We were very impressed with the Dixie design, with their openness, and with all the answers we got on the 550A@24V Dixie DelStar Series 400. If we were buying an alternator today, we would talk to some fleet operators using Dixie and confirm the service life and warranty coverage they were getting was as advertised. If it passes that test, this looks like an excellent product.

And for those of you that like to really push the limits, the Dixie team now has the Series 900 under development and this unit will produce an incredible 880A@24V. We’re not sure we would buy that one at this point but nothing helps give us confidence in the Series 4000 product more than seeing how hard they are pushing the similar Series 900.

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3 comments on “13.2 kW Alternators and Beyond
  1. Howard Weston says:

    I apologize if this has already been asked, I noticed your lifetime engine hours has had an average load of 44%, very impressive. my question is, with your large alternator load, do you notice much extra fuel burn? Versus, running generator and adding hours. Thank you

    • The power required by the alternators is real but it appears to be lost in the noise. 9kw requires about 12hp. If you assume even a very large 40% loss to alternator inefficiencies, it still only requires 18hp when operating flat out. On a 266 hp engine, that’s a fairly small percentage of the overall output and, in the normal case, the alternators usually aren’t maxed out for long. The average draw is closer to 5 to 10 hp and it just gets lost in the noise.

      However, it is a computable number. 10hp on our engine requires just about exactly 0.5 gallons per hour.

      The second half of your question is which power source is more efficient. The generator is more efficient with the alternators releasing more energy to heat. The advantage of the alternators, 1) the main is already running and actually could use more load, 2) the generator would be operating for much of the time in a very low load situation, and 3) the generator hours mount fast if you use it 24×7 when underway which leads to more oil changes, more maintenance, etc. I prefer to run fewer engines and have less to service so chose to use the main engine to support the house loads when underway and only use the generator when on anchor.

  2. Eric Patterson says:

    Nice article! Did you measure decreased output at higher temps at similar speed? Also, that DixieDelStar is a sweet package. Wow, if the main could handle it and I could get the right battery that’s a nice option underway.

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