How to charge 2 batteries

[Rock Hall]

My guest shore charger died this year. It was designed to charge 2 different banks of batteries. I also have a Perko 2 battery switch. 2 new Deep Cycle batteries.

I have a new charger, the automotive type, that is automatic 12/8/2 amps. I would like to mount this in place of the Guest charger. Can I do this? The Guest has 2 outputs for the batteries. I havent figured out exactly how this is wired, but I think the charge leads go into the battery switch. Can I use this arrangement safely and effectively?

This is an '89 Searay with a Mercruiser.

Any help is appreciated.

Mark

 

[Barnacle_Bill]

Re: How to charge 2 batteries

Not a good idea. Automotive chargers are not sealed against water and sparks. Plus they won't take the abuse a charger gets in a boat from waves.

 

[Silvertip]

Re: How to charge 2 batteries

A little more info please! You said you have two deep cycle batteries and you have a Mercruiser I/O. Are you implying that one of the deep cycles is being used as a starting battery? Unless its labeled "Dual Purpose" that's not a recommended application for a deep cycle. Yes -- people do it but deep cycles should be oversized by about 15 - 20% when used for starting purposes. As for using your charger, the simplest way is to connect it to one of the batteries. Set the Perko switch to BOTH and both batteries will charge. I'm with the others however. That charger will not last in a marine environment, nor is it safe.

 

[QuadManiac]

Re: How to charge 2 batteries

Not a good idea to charge two batteries with one charger source, simultaneously, UNLESS they are the same brand, type and age, and are used for the same purposes with equal use. Otherwise, one battery will aways overcharge and the other will always undercharge invariably leading to premature failure of both.

Best is to charge each independently with one charger or to get a charger with multiple outputs, so both batteries will be charged correctly, and will provide you with best performance and the longest possible life.

Good luck!

 

[Silvertip]

Re: How to charge 2 batteries

Got to disagree on the charging parallel packs with a single charger but the topic is not worth debating as there are simply too many of those systems performing perfectly well with dissimilar brands, varying ages, and varying sizes. I do agree however that the same types of batteries should be used in the pack. The current crop of smart chargers do a great job of handling this situation.

 

[bruceb58]

Re: How to charge 2 batteries

It is ok to parallel charge two batteries of different size. As long as they are the same type battery chemistry you are fine.

 

[Rock Hall]

Re: How to charge 2 batteries

Here's some more info

Both batteries were purchased and installed at the beginning of the season. They are group 29 Deep Cycle. I was going to buy a seperate starting battery and still might, but my engine is pretty new, in good shape and I rarely have to crank it more than 2 sec to start.

I guess what I was really asking is if this could be done without an isolator.

To some it up, there seems to be enough of you that feel that the system would be unsafe and the charger probably wouldnt survive, that I think I'll scrap the idea. I thought I had found a way to use a nice feature rich automotive charger in my boat and do it cheap.

I think I'll just buy the ProSport 8 amp here from Iboats and do the job right. Iboat's price is a lot lower than everyone elses.

I have this bad habit of trying to devise a way to do something without spending lots of money.

The other project I'm looking into is an Inverter. Does anyone have any experience with a non-marine inverter? Good or bad?

Thanks for all the suggestions.

Mark

 

[Silvertip]

Re: How to charge 2 batteries

Again, if you are thinking permanent installation you are looking at the same situation as with the charger. Marine electronics are sealed for two reasons. Sparks and moisture protection. You know the old adage -- electricity and water don't mix. Consider the safety of your guests. What do you need to run that requires 110 AC?

 

[Rock Hall]

Re: How to charge 2 batteries

My engine room is pretty dry. I've never had any thing down there get wet. I've heard of other people using regular inverters in their boats, I hoped to get some feedback.

I have a TV that acts up on DC when the voltage isnt over 12v. Not much tolerance for voltage fluctuation.

Probably a quick and simple help to my problems would be a 3rd starting battery. Then I can run the 2 deep cycles in parallel and shouldnt have to worry about the voltage dropping for quite some time.

Thanks for the info.

Mark

 

[QuadManiac]

Re: How to charge 2 batteries

It is ok to parallel charge two batteries of different size. As long as they are the same type battery chemistry you are fine.

If you wish to have a discussion on physics and electro-chemistry as it relates to batteries and why this is NOT the most favorable way to charge them, I'll be glad to write a 10 page treatise.

They WILL work just fine, as evidenced by the many that do it this way, but life expectancy WILL be reduced, as defined by the science.

Rock, in your case, with nearly identical batteries, I would have no reservations. However, what Silvertip says about marine vs garage hardware is the issue to be concerned about.

This is an issues especially when it comes to inverters. In one of my recent job duties, I attempted, under contract to the Army, to find a commercial, off the shelf inverter that could be purchased in quantity and sent into the war zone quickly. One of the tests that we performed was safety in the presence of moisture. Quite a few exhibited very dangerous voltages at the case when even slightly wet. I would be very careful when using commercial 110VAC electronics in a marine environment.

Good Luck!

 

[Rock Hall]

Re: How to charge 2 batteries

Quad,

Thanks for the advise. I think for now I will add a third battery and get a small portable inverter to use in the cabin when I run the T.V. and take it home with me when I'm done.

Mark

 

[Silvertip]

Re: How to charge 2 batteries

Quad -- there is undoubtedly a gazillion pages of wet, dry, and gel battery theory on the web so save yourself the trouble. This charging technique has been used on virtually every vehicle and boat on the planet for years with no ill effects within the limits that have already been discussed. However, I like to read so have at it.

 

[Rock Hall]

Re: How to charge 2 batteries

With a Perko 2 battery switch, are both batteries charged all the time or only the one that is selected? I would think there would have to be some kind of an isolator somewhere.

I'm interested in how this works with a shore power charger and an alternator.

 

[QuadManiac]

Re: How to charge 2 batteries

Quad -- there is undoubtedly a gazillion pages of wet, dry, and gel battery theory on the web so save yourself the trouble. This charging technique has been used on virtually every vehicle and boat on the planet for years with no ill effects within the limits that have already been discussed. However, I like to read so have at it.

This is a point that I can't argue Tip, it IS done almost universally... But just as universally, people have to replace their batteries when they fail. A good percentage of those people feel that they SHOULD have seen more life out of their batteries before failure.

I've simply been trying to descirbe one way in which they CAN.

Nuff said.

 

[QuadManiac]

Re: How to charge 2 batteries

Quad -- there is undoubtedly a gazillion pages of wet, dry, and gel battery theory on the web so save yourself the trouble. This charging technique has been used on virtually every vehicle and boat on the planet for years with no ill effects within the limits that have already been discussed. However, I like to read so have at it.

This is a point that I can't argue Tip, it IS done almost universally... But just as universally, people have to replace their batteries when they fail. A good percentage of those people feel that they SHOULD have seen more life out of their batteries before failure.

I've simply been trying to descirbe one way in which they CAN. Configure your batteries any way you choose. My respect for you will remain intact.

Nuff said.

 

[Big Keepers]

Re: How to charge 2 batteries

With a Perko 2 battery switch, are both batteries charged all the time or only the one that is selected? I would think there would have to be some kind of an isolator somewhere.

I'm interested in how this works with a shore power charger and an alternator.

I'd scrap that Perko 2 battery switch and use the Blue Sea add-a-battery system. I've posted the info on it a few times on these boards. My way gives you a battery strictly for starting the motor and a battery strictly for powering up 12V DC accessories. The system comes with a link that monitors both batteries as the motor is running and applies the alternator's charge to the battery that needs it most. The switch is on or its off. In an emergency there is a combine both option that connects both batteries to give you enough amps to crank the motor and get it started. It also has a starting isolator in it so when you crank the motor there is no surge backwards that can harm your electronics.

With the Perko on/off/both switch, unless its on both I'd say only the battery selected is getting juice.

 

[bruceb58]

Re: How to charge 2 batteries

If you wish to have a discussion on physics and electro-chemistry as it relates to batteries and why this is NOT the most favorable way to charge them, I'll be glad to write a 10 page treatise.

They WILL work just fine, as evidenced by the many that do it this way, but life expectancy WILL be reduced, as defined by the science!

I have done a lot of work with batteries with past jobs(I am also an electrical engineer). If you are talking about getting the last 5% out of batteries, then you have a point. The problem is that you can buy two identical batteries off the shelf and they will have slightly varying charge characteristics. For a miltary environment, this can be critical...for a marine environment...not worth losing sleep over.

 

[QuadManiac]

Re: How to charge 2 batteries

Bruce, you are probably right there... I spent WAY too much time making sure that soldiers didn't screw up their HMMWV's readiness by dong something stupid with their electrical system. Quite typical was hooking up a 12V inverter to one battery in thier 24V system to run their Mr Coffee machine, or a small refrigerator, lol. Then they wondered why they kept having starting issues.

 

[bruceb58]

Re: How to charge 2 batteries

Have to agree with you on that! My first engineering job 25 years ago was military. We had to make sure when we wrote any manuals to keep as many words under 3 syllables as possible