DC power through shorepower

[Shack]

I want to burn DC lights and radios while in port, but wish to spare the amps in my batts. I do have shorepower.

I could link my DC system to my shore power via a battery charger or transformer.

Simplest would be to just plug a battery charger into the AC recepticle and plug the DC end into the cigarette lighter. More involved solution would be to hardwire a transformer in between the AC panel and a battery switch.

Anyone have any recommendations?

Thanks.

[PBzeer]

I have mine set up so that my charger is connected not to the batteries themselves, but to the common lead from my selector switch. This means the charger is running the DC system when I'm plugged into shorepower.

[Shack]

PB,

I have an available terminal on an extra BATT SW that, I suppose, I could do something similar as you did.

Here's my config (inherited ):

MAIN BATT Switch:
pos1 to Battery #1
pos2 to the 2nd BATT SW

2nd BATT Switch:
pos1 to Battery #2
pos2 to nothing

I leave the MAIN BATT Switch on "Both" to pull from both batts so long as 2nd BATT SW is in "pos1" or "both".

I think that I could just hook in a Battery Charger to the pos2 of the 2nd BATT SW and treat it as a 3rd Battery.

HERE IS MY CONCERN.
If I were to position the above switches so that my batteries were isolated (not in the system) would the battery charger sense a "dead battery" and put out a harmful amount of current? Am I gonna blow CB's?

Thanks,
Matt

[hellosailor]

Matt, I'd be reluctant to use a common charger as a DC power supply (with no batteries involved) only because they may run higher voltage than your DC devices really want to see.

On the other hand, how smart is your charger? If you have a charger which is going to put out less than 1/10th of the rated capacity of your batteries, they can pretty much float on that forever without being used. In which case, I'd leave that charger running and let the DC devices run from that battery while it was being charged. Odds are the charger will supply all loads and the batteries will never notice a thing.

"Odds" depending on things like how smart the charger is, of course.

If you don't plan to do anything with battery switch #2, I'd disconnect it and move the 2nd battery bank over to switch #1, position #2. Just in the spirit of cleaning stuff up.

[Shack]

HelloSailor,
I have my eyes some chargers. I'd like to install one permanently so that I easily flip a switch or two and power-up my DC for those work days on the boat where I have the radio going all day long and lights at night.
So far, the reviews on the "Guest" products a West Marine are pretty sorry.

I was hoping not to spend $300+ on a charge for this either.

Good point with the clean-up of the second BATT SW. But right now it all works (bird in hand?). One of the last owners put the switch in and conected it to a DC outlet, and I kept in there in case it came in handy to add something else later . . . maybe a battery charger?

-Shack

[sailingdog]

Shack-

My setup is the same or pretty close to the way that PBzeer has his setup. The batteries act to level out the voltage changes from the charger quite a bit... and also having them connected this way is a good way to top off the batteries, which is usually not done as often as it should be.

I'd avoid setting up the charger as the "third" battery. It adds unnecessary complexity to your electrical setup, and really doesn't add value to it IMHO. I'd also agree with Hellosailor about simplifying your electrical system as much as possible... the more you have there...the harder it is to trouble shoot.

BTW, I'd go with Xantrex, which is a much better design than the Guest chargers are IMHO.

[Shack]

Thanks Dog and all else,
This is the one thing I like about this forum. Its almost like sitting at the pub or tiki bar. All I need is a Guinness . . .

. . . that is easily being rectified.

Thanks again,
Shack

[labatt]

Sorry... just to ask a stupid newbie question (as I'm learning)... is this statement correct? When hooked to shore power, you are still powering your DC appliances and other DC devices using the batteries, while your charger is charging the batteries using the AC charger.

[PBzeer]

labatt - depends on how you have the charger wired into the system. To expand a bit further on mine, I'm running a 20 amp Truecharge charger (smart charger). The lead goes to a fuse block, then a terminal to which the common (both) from the battery switch is connected, as well as the windlass, distribution panel, and starter motor leads.

In this configuration, the charger "senses" the load when using DC power and supplies the needed amps. This means that even in the OFF position on the battery switch, my DC is still "hot". It's important to remember that when working on the DC, as the charger must be turned off, not just the batteries (at switch or by disconnecting). Hope that gives you a clearer picture.

Shack - check on sailnet, Defenders or Jack Rabbit for a charger. West is the last place to buy something of that nature, pricewise.

http://www.defender.com/
http://www.jrenergy.com/(m1h0ms55g15...)/default.aspx

[sailingdog]

Originally Posted by labatt

Sorry... just to ask a stupid newbie question (as I'm learning)... is this statement correct? When hooked to shore power, you are still powering your DC appliances and other DC devices using the batteries, while your charger is charging the batteries using the AC charger.

Technically, if the shorepower is live, then no, I'm not running the DC appliances off of the batteries... I am running them off of the charger, which is also charging the batteries while I am doing it.

However, this is only true until I get the electrical load on my DC-system up to 20 amps, at which point, I am using more juice than the charger can provide, and will be drawing on both my batteries—to supply the current in excess of 20 amps, and the charger...and my batteries will no longer be charging at that point. I've never reached that point, as my electrical needs are relatively light...and I've gone to mostly LED-based lights, and use other measures to minimize my electrical loads.