Charger / Inverter

[95yj]

I have a 23' express cruiser. In addition to using electrical when moored near offshore, I will have the boat moored in a slip and will be using a minimal amount of electrical. A few 12 volt lights, the radio,maybe a fan and at 120vac a laptop or small tv. I have shore power available, but there is nothing set up in the boat for it.

Instead of spending $600 - $1000 on a marine inverter / charger I was wondering about some other options. I have a Schumacher fully automatic 10 amp charger with settings for maintenance free and deep cycle. I would be wanting to use it more as a generator when using 12 volt items while docked. Would it be acceptable to permanently mount this in the boat? I would not leave it plugged in continuously when away from the boat.

Secondly is the function of an inverter vs. shore power. When out of the slip, I would want to be able to power a few small low wattage items. Same when in the slip. I would like to wire an outlet in the cuddy to 120vac. A switch in one position would power the charger and the outlet from shore power. In the other position, the outlet would be powered from the inverter. The inverter could be a decent quality, inexpensive shelf model.

I'm looking for suggestions along with reasons I can or cannot do what I'm planning. Also other considerations like the 120vac outlet type and wiring in a saltwater marine environment. Same with the shore vs. onboard power switch.

 

[Silvertip]

Re: Charger / Inverter

There is one potential and deadly problem with your plan. Without an isolation transformer in the AC system you leave yourself wide open to shock from improperly installed shore power. That's why those big inverters get expensive. It shouldn't happen but it can. I used to see it all the time at campgrounds -- especially the Mom & Pop types where Pop was a better mechanic than an electrician. Reversed polarity and improper grounding can kill you. If it were mine, I would install a "marine" smart charger with two banks. One for the engine start battery, and one for a second auxiliary. Add a battery switch or isolator to allow running accessories from the auxiliary without draining the start battery. You simply plug into shore power to provide all the 12V power you need. The small inverter (minus the AC outlet idea) would apparently meet your AC needs. There is no need to switch the AC to the charger because it's smart and can be left on indefinitely.

 

[95yj]

Re: Charger / Inverter

FIrst thanks for the information Silvertip. Also found another problem with my proposed charger. There's a disclaimer on it about internal relay and switch circuits that produce arcs and sparks. Not a good combination inside the hull of an I/O boat.

Combining this post with my other regarding a battery switch, let me sum up what I believe you have recommended:

Shore power comes into an outlet that only powers a two bank marine smart charger. Each bank is wired separately to each of the two batteries. Off,1,2,both switch is installed between the two batteries. All 12 volt circuits are powered from the common on the switch enabling operation from either battery. When boat engine is running, switch is in both position to charge both batteries. Switch is in 1 position to start boat from regular battery. Switch is in 2 position to power all accessories including 120vac from inverter from deep cycle battery when engine is off whether on shore power or not. Bilge pump is wired directly to deep cycle battery.

What happens with a two bank charger when plugged into shore power if the battery switch is switched to both effectively connecting both banks of the charging circuit? I realize the switch should be switched to 1, 2 or off, but what happens upon incorrect sequence of plugging in verses throwing switch?

Can you recommend a decent inexpensive two bank charger?

How big an issue is galvanic corrosion if plugged into shore power only every so often? I do not plan on using shore power unless I am with the boat and indeed I actually plan on storing the boat at the marina out of the water instead of in the slip during most weeks.

 

[Silvertip]

Re: Charger / Inverter

There is no problem with switching the battery switch whether or not shore power is connected to the charger. You are correct with the single AC connection to the on-board charger. You are also correct in its operation. The outputs of the two bank charger connect directly to the batteries so they can be supplying power while you are consuming power. Modern two bank chargers have isolated outputs so you can parallel them or series them if you needed 24V. You can buy one, two, and three bank chargers right here on iBoats. Guest is just one brand but there are others. I use Guest chargers and have had zero problems with them. My walleye boat is layed up for the winter but the charger is connected as we speak and will remain connected until ice out. I would suggest that 10A per bank is sufficient. I'm a fresh water guy but someone will come along with saltwater experience if you post a separate question regarding galvanic protection. Doing it this way creates a safe system, keeps it simple, and its versatile. If you do end up needing some high power AC accessories, then its probably time to look more seriously at adding an AC system.

 

[Dunaruna]

Re: Charger / Inverter

[colour=blue]Salt water is worse but galvanic corrosion & electroysis is also an issue in fresh water (I've seen alloy toons eaten away in 3 months due to the following) and the biggest culprit is the boat next door (leaking grounds) or bad/leaking grounds on the mooring. A really badly installed gen set (once again, the boat next door) will also cause problems.

You mentioned a laptop, be careful when purchasing a 'cheap' inverter, some laptops will only operate with true sinewave inverters - AKA, expensive.