12v Power Supply verses using batteries

[Lucky Dog]

I have removed the partly rusty rats nest of wires encased in wasp nests. Rebuilding everything. On paper I have planned to use a 12 volt power supply when tethered to shore power. This reduces the cycling on the house batteries. To my surprise the marine box stores doesn’t carry 12 volt supplies. I have found industry standard products that are less expensive than the batteries. It does complicate the wiring, but it can be done.

My question; How many of you use a power supply?

Thanks

ml

 

[TRMN8R]

I have removed the partly rusty rats nest of wires encased in wasp nests. Rebuilding everything. On paper I have planned to use a 12 volt power supply when tethered to shore power. This reduces the cycling on the house batteries. To my surprise the marine box stores doesn’t carry 12 volt supplies. I have found industry standard products that are less expensive than the batteries. It does complicate the wiring, but it can be done.

My question; How many of you use a power supply?

Thanks

ml

Not quite sure what it is you're trying to accomplish. You can switch off the batteries from the charging source, at least I can, to reduce cycling. If you're just trying to build a line source to low voltage converter, after you're all said and done, with the work and expense of it all, is it really worth it? If you're 'rebuilding' then why not lay in AC shore power with a couple outlets to use dockside? A Marinco inlet, with ABYC approved switch, simple 3 circuit Blue Sea (or otherwise) panel, some ABYC approved AC wiring (maybe an electrician friend can help with the layout, etc), and you'll probably be at the same dollars wouldn't you think?

 

[treilley]

I think what ml is trying to avoid is running down his batteries while running 12v devices while at the slip. He then needs to recharge the batteries.

I have the same setup although I am not at a slip so I just run my charger when plugged into shore power and using 12v devices.

He is looking for a reverse inverter(is there such a thing? Would that be a transformer?). 120vac to 12vdc.

 

[Maine Sail]

There's really no need

There's really no need to do that. With a well built and properly sized 3 stage battery charger you can run your 12V devices and not discharge the bank. The newer three stage chargers, with float mode, can be left on nearly continuously and not cook the batteries.

Most 120V to 12V power supplies are limited in the amps they can put out and get very expensive very quickly. With a good charger you should never even get close to a 95% depth of discharge even when using 12v items while charging.

The battery charger is usually sized according to the type and size of the battery bank it is charging. Buying a "cheap" charger is generally a really bad idea, since it will often shorten the life of the batteries with it's lack of float mode or multi-stage charging.

What you need is a good smart charger. This means that the charger will go through the bulk, absorption and float phases of charging and step the voltage and amperage up/down as the charge level on the battery changes.

You did no describe or state how many amp hours your battery bank is or what type they are. The general rule of thumb for sizing is that the battery charger should be roughly 20-25% in amperage capacity of the 20-hour amp-hour rating of the battery bank. For instance, if you have a house bank of two 12 volt batteries, that would have a capacity of say 200 amp-hours, you'd want about a 50 amp charger, give or take.

It gets more confusing if you are using AGM batteries. These batteries have a much higher current acceptance rate meaning they can accept and take an entire 200 amps or more in an hour. If you have AGM's you might want a larger charger to utilize their higher current acceptance rate in the bulk phase or first phase of charge

You'll want a battery charger that can be set for the specific voltage requirements of the battery type you are using whether it be, wet, Gel or AGM. Not setting a charger up correctly can actually shorten the life of the banks.

I really like the Iota brad of chargers, sold mostly through "off the grid" companies. The 30 amp charger is about $127.00, the 45 amp unit $142.00 and the 55 amp is $167.00. Well built and reasonably priced.

Iota Chargers (LINK)

 

[Lucky Dog]

Electrical needs/desires

If you don't ask, you won't know, so....

Planning the Charger/inverter - freedom-hf1800 by Xantrex
and gel batteries.

I did not understand that a charger could keep up with those loads.

I am trying to create a system that a "helpful" guest doesn't fry something out. One switch that controls the electrical circuits.

I have included the work sheet i did following Don Casey's book to determine battery amps. The shore power would be less and microwave time more.

thanks and you guys are great.

ml

 

[rwthomas1]

I am rarely on a dock however when I am, and plugged into shore power, the Xantrex TrueCharge 20 amp battery charger has easily kept up with the demands of running the AB reefer system, lights, etc. and tops the batteries off full. Xantrex makes a really cool inverter/charger that is the same size/shape as a group 31 battery http://www.xantrex.com/web/id/243/p/1/pt/7/product.asp The way I see it a small charger should keep up easily with house loads. Reefer and a few lights is 10amps/hour tops. Even my old charger is capable of 20 amps/hour? If you are plugged in for a long time, like most dock dwellers, then the charger has DAYS in most cases to charge the bank? Or am I missing something? RT

 

[Maine Sail]

On shore power

On shore power you would not be running a lot of the stuff on that list like running lights, plotter, AP etc. and the microwave and coffee maker should be run off shore power when dock side not an inverter.

Your real concern is when you try and use 233 amps per day while out cruising. Putting 233 amps per day, back in, when away from the dock, is NOT an easy task and will require MUCH $$$ in battery bank and alternator/solar/wind or generator.

If you figure an 80% max re-charge rate when away from the dock, it takes HOURS AND HOURS to ever get back to 100%, you'll need a minimum bank size of about 600 amp-hours for just one days consumption. For two days you'll need to double that. To do this you'll also need one heck of a honking alternator and a battery bank designed to accept a very high rate of charge, like AGM's ($$$$$), so you don't need to become a trawler and need to run your motor constantly.

What you really should get, before you do anything, is a battery monitor like the Victron or the Link series from Zantrex so you have real consumption numbers to work off of and a better understanding of how a battery accepts current and what the charge characteristics really look like.

I've yet to meet very many boaters who hit it spot on with a Don Casey energy budget calculator. You may even be off by as much as 40 or 50% in your favor which is not uncommon.

I would be very, very surprised if you even burned 20-30 amps DC per day while at the dock provided the AC stuff is running off AC and the DC off of DC.