DC DC starter battery charger on Amel 55 fuse sizes

Billy Newport

My generator wouldn't start last weekend so on poking around, the starter was weak. I could start the engine and then I could start the generator. On checking why the starter was weak, the DC-DC charger output side (#3 under the nav seat) was blown. It's a 15A fuse. So, no charger, dead battery, gen won't start. Ok.

Looking at the Victron manuals for an Orion 24/12/25 DC DC charger. It has a normal bulk output current of 25A with a peak output of 35A. Why have Amel installed a 15A fuse, it's even labeled 15A.

So, I left the boat this week and when I came back today, the 15A fuse I replaced is blown again. I discussed with BillR and for now, I've replaced both fuses with a 20A and a 40A (don't have a 35A). Now, given what I can figure out, I don't know how this ever worked but clearly the boat is 4 years old and has 20k nm on it. I've sent an email to Denis, the old owner asking what gives.

Do the alternators on the gen OR engine charge the starter battery? Is it just the DC-DC charging it?

The cables are 10 gauge wire. I can't see how long they are. 24V @ 20A is no problem for 10 awg. 12V at 25A is good at 10 feet long with 1% V drop.

Amel 55#56

Clive Chapman

I know nothing about Amel specific electrics, but a fuse can also protect the wiring. Is it possible the cabling is only rated at 15A? The danger with uprating the fuse is you could create a fire risk because the wiring now effectively becomes the fuse (sorry if this is teaching you what you already know). 

Billy Newport

I thought about that but then why use a 25A charger, the whole thing would be pointless. The charger puts out 25A, the wiring supports 15A, use a 15A fuse and pop...

The unknown on my side is how long is that wire. I'll try trace it better today.

Joerg Esdorn

The electrical plans confirm this is a 15A fuse.  I would contact Stephane at Pochon and ask him your question.  Pochon designs all the electrical systems for Amel.  Stephane is the client relations guy for all Amel owners.  stephane@...

Good Luck!

Joerg Esdorn
A55 #53 Kincsem
Vigo, Spain

John Clanton

Joerg’s advice is the first thing I thought of when reading the original post.

The fuse size is not the problem. As in all things Amel, there is logic in why that particular fuse is 15 amps, even though it is not obvious to the rest of us.

Once resolved, please post the underlying problem as well as the logic that does not seem obvious.

Fair Winds,

SV Devereux
A55, No.65


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Ken Powers SV Aquarius <ken@...>

Was the Orion charger an upgrade?  Check the battery.  The start battery should not be discharged just because the start-battery-charger goes down.  Unless there is a short somewhere.
1A. Replace the fuse with a 15amp fuse.
1.  Check there is no short or leakage in the start circuit for the Genset.
2.  Check there is no short or leakage in the start circuit for the Engine.
3.  Try a different battery for the start circuit.
4.  Check to see if there is a short in the key switch for the engine start.
5.  If, nothing fixed the problem, there is probably something wrong within the Orion Charger. 

I don't believe that the start battery should be supplying current to anything with the engine off and the genset off.  Even if your charger went dead for 10 engine starts, your battery should be able to handle it.

Just my thoughts.. 
Hope you find the problem.

Ken on Aquarius SM2K #262

Billy Newport

I emailed Stephane and got the following response back.

"Good Morning Billy,

I am Ioera from POCHON PRO design office.


On AMEL55, the standard inverter DC/DC is a MAGIC 24/12-20 (MasterVolt).

When this device works in chargins mode (3-step mode) the output charge current is 16A.


This explains the fuse value of 15A.


I stay at your disposal for any further information.


Best regards.




Bureau d’Etude POCHON PRO"

So, the victron seems to be an after market upgrade which basically never worked as it blows the 15A fuse very quickly. I'm looking for a replacement charger then to fix the issue.


Joerg Esdorn

Looks like you've found the problem, Billy.  My understanding is that the Amel 55 initially did not have this DC to DC charger, with the engine alternator being the sole charging source for the starter battery.  This resulted in the starter batteries going bad when boats weren't moving for long periods - the specs for the AGM say that the self discharge rate is 3% per month. So you also might have a sulfated starter battery because it has been deep discharged many times and never been charged to 100% by the engine.  Good luck with fixing your issue!  Cheers Joerg

Joerg Esdorn
A55 #53 Kincsem

Billy Newport

To conclude this.
I called Cay Electronics, my local Mastervolt dealer/installer. They didn't have the Magic 24/12/20 DCDC charger but recommended a Victron 24/12/25 instead. I mention I have one of those but the wiring @ 10 awg worried me given 15A vs 25A. They indicated 10 awg is fine for 25A, it's a voltage drop problem vs a safety/fire risk. 10 awg at 25A would be between 5 and 10% voltage drop which they think is fine for a charger so they would change the fuses to 15A (24V side) and 25A (12V side). I'll do this and see how it goes.