Re: [Amel] Battery Chargers and Inverters


I like the way you are thinking about this, Steve.  You have a great way of making it seem simpler again.  I'll let you know what I end up doing.

From: Steve Constantine <svsummerlove@...>
To: "amelyachtowners@..." <amelyachtowners@...>
Sent: Monday, February 25, 2013 5:05 PM
Subject: Re: [Amel] Battery Chargers and Inverters

Hi Kent,

There's no question a 100A charger or two will reduce the charge times.  The way I see it though, is if I'm running the genset for 1.5 hours anyway to do other things, what have I gained by shortening the charge time?  For example, if I'm drawing 30A from the genset, I'll charge the batteries in half an hour, but I won't be able to run anything else.  I'd then have to continue to run it for another hour after the batteries are charged to cook dinner in the microwave, wash the dishes, and run the water heater for my shower.

When I decided to buy an Amel, a lot of it had to do with buying into the Amel philosophy.  Unlike other boat brands and models that last a few years on the market, this one had been designed on a world cruise, and then refined and improved for 15 years after that.  They'd pretty much got it figured out.  I really liked their on-board power management system.  It has a 7KW genset big enough to support all the appliances for comfortable living aboard, an enormous battery bank, and an inverter wired for times when the genset doesn't make sense.  Then they added a fuel tank big enough to support it all over a long ocean passage.  If the genset fails, there's the main engine as back-up.  Why change or complicate it?  

A well-designed battery plant starts with your consumption requirements (AH per day), and backs into the total AH capacity of the batteries and charger size that's required to achieve them; not by figuring how many amp hours can be fit into the battery box, then deciding how many chargers are required to keep them lit.  Your requirement is the same as mine... 130AH (and I think a lot of other SMs as well).  With 420AH in your batteries, that's about 31% of your capacity in a 24 hour period.  To replenish 130AH on a single daily charge, you'd have to run your 60A and 65A chargers for approximately 1.5 hours, assuming you let the batteries discharge to 50% before you start to charge them, and take them up to 81%. 

Regarding using the existing wiring for the new charger/inverter, you're probably OK re-using the 220VAC output cables from the inverter, and the 220VAC input and 24VDC output cables to the charger as long as you don't go any bigger than 65A.  If you go with a 100A charger, you'll probably need larger output cables.  However, for the 24VDC inverter input it's crucial to have the cables sized large enough to prevent voltage drop.  You can't just pick up 24V from any convenient terminal unless it's also being fed by large enough cables itself.  Where is your Heart I/F currently mounted (engine room, nav station)?  The best installation is to run a dedicated pair of cables (pos and neg) directly to the inverter input from the main battery switches using crimp connectors installed with the CORRECT crimping tool.  You should also have a correctly sized fuse (not a breaker) mounted as close to the battery end as possible on the + cable.  The fuse is
to protect the wiring, and NOT the inverter.  On a 4KW inverter, that's probably in the region of a 300A fuse.  If you've ever seen a direct short of 24V @ 300A to ground, you'll understand why it's there.

Regarding running two chargers in parallel.  It's not easy to get multiple charging devices to load share over the entire charge cycle, unless they were designed for it.  Like gensets, they run more efficiently when they are cranking out close to their capacities.  They will both pour the coals to the batteries at the start of the charge when the batteries are low, but as the current is reduced, they'll probably start to run less efficiently than a single charger.  You could maybe monitor the charge and experiment with turning one off at different points until you find the right balance.

I hear you loud and clear on your reluctance to pay an electrician to learn about Amel wiring.  I've found the best way is to figure out everything I can, then pay him to confirm what I think I now know.  That said, there's a case to be made for his expertise in safe electrical procedures and the specialized tools you won't have to buy or rent.  I think the best compromise is to know exactly what you want him to install, have all the obstacles out of his way and all the parts ready to go before he starts, then pay for him to do it safely and correctly.


From: Kent Robertson>
To: "">
Sent: Monday, February 25, 2013 10:24 AM
Subject: Re: [Amel] Battery Chargers and Inverters

Steve, that's a great explanation of our systems. I was looking at a 2500 W inverter because that's what my old Heart Interface charger/inverter had. I was looking at 100A charger on advice of others who've said it reduces their charge times. The old one was 65A. My usage is similar to yours, about 130 AH per day. My 420 AH battery bank would be pretty low if I tried to charge only once a day, but if I had a larger bank I could probably do it. The batteries I have are group 27 and a little larger than the group 31's, I think.
What kind of stand-alone inverter do you have? The Magnum charger is the one closest to the 100A / 2500W inverter that I could find. If I could find a 2500W stand alone inverter, that's what I'd do. Would I be able to use the same wiring that I have from the old Heart Interface? I'd need a 220 input for the charger, a 24v output from the charger (both from the old wiring), a 24V input to the inverter (which I could take from the 24V studs on the foreword bulkhead in the engine room) and use the 220V output cables from the old Heart. Am I missing something here? The old Heart had a 65 A charger, so maybe larger wires to the battery bank if I got a 100A charger? I guess if I got another 65 A charger I could run that one and the Charles 60A together for 125A during the bulk charge.

It looks like I should probably find a good electrician to help me with this, but I hate paying someone for hours of figuring out how Amels are wired, and I've not had much luck finding anyone in Brunswick who seems to know anything about European wiring. Has anyone had a good experience with an electrician from Jacksonville or Savannah?
Thanks again for all your thoughts and help.
SM 243

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