Installing an on board charger help needed.

[RandyBC]

I have a Charles 40A SP5000 charger that was removed from my sailboat when I installed an inverter. I want to install it on my Trophy 2352 to keep the batteries charged when at a marina and when in the shop. Heck, I have it sitting there and I think it would be perfect for my fishing boat.

I had a question.

I would like to be able to plug it in to 30A power which is the most widely available at the marinas in our area. That means installing a 30A input receptacle on the boat. The charger itself has the following specs:

AC input amps: 9A
DC output amps: 40

Can I use the 30A input without blowing the breaker which will probably be a 10A?

 

[KD4UPL]

Re: Installing an on board charger help needed.

If I understand you correctly, you would place a 10A breaker between the shore inlet and the charger? That would work but it's really close to the 9 amps the unit draws. I would probably recommend a 15A breaker instead.
Don't worry about the fact that the shore power is 30A. That's it's maximum capacity. It will only supply what you draw. It's not like voltage, which sort of "forces itself" on whatever is connected to it.
I'm not sure how to explain it exactly so it makes sense. I'm a master electrician so it all makes sense in my head but it doesn't always translate.

 

[RandyBC]

Re: Installing an on board charger help needed.

Great answer, that is what I thought and was hoping was the case. The charger came off a boat with 30A input so I was pretty sure I would be ok but your helpful answer confirms that! Thanks so much!

Its not imperative to my installation but how does the charger bring a low current of 9A and turn it into a relatively high current of 40A?

 

[stevecur]

Re: Installing an on board charger help needed.

The output is 40 amp DC. About any charger will work fine on 15 amp breaker. A car charger that does 130+ amp boost for jump starting has no trouble on 15 amp.

 

[KD4UPL]

Re: Installing an on board charger help needed.

Its not imperative to my installation but how does the charger bring a low current of 9A and turn it into a relatively high current of 40A?

What you need to look at is overall power, or watts. The input to the charger is 120v at maybe 8A which is 960 watts. It's probably around 80% efficient so it should be able to put out around 768 watts. 768 watts/ 14.8 volts = 52 amps. Obviously, I don't know the exact draw or efficiency of your charger but you get the idea.

 

[glenn property of pam]

Re: Installing an on board charger help needed.

breakers protect wires so the 30 amp supply available at the dock may be to high for the cable going to the boat and in the case of a short the cable may melt before the breaker trips.
The charger is rated at 9amps and that is all the charger will draw so it doesnt matter if you plugged it in to a 100 amp circuit it will only use 9amps of it.
either reduce the available ampage (breaker) at the dock or use a 30 amp cable then reduce the ampage (breaker) at the boat. a plug in 30 amp to 15 amp breaker/gfci will work fine.
on a side note: all shore power wiring on the boat must meet marine wiring standards

 

[RandyBC]

Re: Installing an on board charger help needed.

I plan on using a 15amp breaker and 12 g wire on the AC side and 6g wire on the DC side with 50 amp fuses near the batteries. All wires will be marine grade. What other standards do I need to be aware of?