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Old 08-06-2014, 08:34 PM   #1
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Question 12V Power Supply for 12V Systems

Esteemed and all knowing members,

I have been pondering a simple question:

Why wouldn't a 12v 24 amp power supply work in place of the battery bank when connected to "shore" power?

At present we have two 12v house batteries in parallel and still have 12v power weakness (voltage goes below 12v) after several hours with the "usual" neon lights operating.

I'm planning to replace most of the neon & incandescent lights with LEDs, but I also wondered why I couldn't use a big 12v power supply running on AC when connected to shore power.

Your thoughts and suggenstions are MOST welcome.
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Old 08-06-2014, 09:09 PM   #2
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Most coaches have a converter/charger which does as you describe....it replaces whatever electricity is coming out of the batteries (up to a max limit). Your lights should not be dim when connected to shore power...the batteries should read above 13.1 volts generally.
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Old 08-06-2014, 09:33 PM   #3
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Check that your converter/charger is working by measuring voltage at the batteries when plugged in to shore power. As pasdad1 said, you should have more than 13.1 v when on the converter/charger. If you're not seeing those numbers or above, your converter/charger needs replacing or work. (Check for circuit breakers tripped right on the box the converter/charger is in.

Also, I doubt if you have neon lights, you probably have fluorescent lights. You could reduce amperage need by changing both over to LED lights. Search on iRV2 for threads about converting fluorescent tubes to LED's using very inexpensive components from Ebay.
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Old 08-07-2014, 07:54 PM   #4
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I've had the Xantrex inverter/charger worked on once already - due to a lightening strike. However It doesn't seem to be able to keep the batteries above 12.6v. When I get home I'll call them and see what I may have to do.

Boondockingk and running the 120VAC systems from the battries really isn't in the cards. If I want 120VAC I'll rug the Onan genset.

SO... again What would be the problems using a beefy AC->12VDC power supply instead of using the batteries?

Should I set up a transfer switch?

Is all I really need is a good battery charger for deep cycle batteries? (in place if the Xantrex)
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Old 08-07-2014, 08:19 PM   #5
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Originally Posted by JJH3rd View Post
I've had the Xantrex inverter/charger worked on once already - due to a lightening strike. However It doesn't seem to be able to keep the batteries above 12.6v. When I get home I'll call them and see what I may have to do.

Boondockingk and running the 120VAC systems from the battries really isn't in the cards. If I want 120VAC I'll rug the Onan genset.

SO... again What would be the problems using a beefy AC->12VDC power supply instead of using the batteries?

Should I set up a transfer switch?

Is all I really need is a good battery charger for deep cycle batteries? (in place if the Xantrex)

What model Xantrex do you have....maybe it is a setup parameter that needs changing.
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Old 08-07-2014, 08:35 PM   #6
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In a nutshell the Xantrex is a big 12 V DC power supply. A bit more monitoring and a bit less filtering than a bench supply because the batteries partly replace the filter caps. You can replace it with a power supply but then you will have to manually monitor and adjust the charging voltage. In your case it sounds like the Xantrex is not working or not working correctly. The other alternative is that you are drawing more current than the Xantrex can supply. If that is the case you also need to know that and either reduce current usage or increase the size of the Xantrex.

As far as sizing I would expect the Xantrex is capable of 40-60 A @ 12V nominal, really somewhere between 13.6 and 14 V or so. I just looked at the Xantrex web site. I'd check what model I had then look at the charging current capacity. You are exceeding that number to drain the batteries while the charger is on.
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Old 08-08-2014, 08:31 AM   #7
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Sage advice, as always - thanks for talking me down from he metaphorical cliff.

Here is the information on the Xantrex:
Model 81-1010-12 built 10/11/04

I had it "repaired" after a lightening strike a couple of years ago, and also had a bad cell in one of the house batteries so the bad cell was masking the charging problem. Put new batteries in the coach last year but have been using an external battery charger to keep them charged.

I'm in East Stroudsburg PA right now and will be home Sunday. I'll start talking to the Xantrex tech support Monday and see what develops.

Getting the Xantrex out of the coach is just a little less painful than a tooth extraction.


Thanks guys.
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Old 08-08-2014, 10:04 AM   #8
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I found your model on the Xantrex website. It's a "freedom 458" inverter/charger

The inverter side has 1000W capacity and the charger side is a 50 amp 3-stage.
It has a 10v low battery cut-out.....meaning if it detects voltage lower than 10, the charger shuts off completely. It also says it has temperature sensitive charging....so you might want to find if the thermal sensor is hooked up and where it's located. If the thermal sensor reports high temperatures, it cuts back the charging.

You would also want to check that it's battery type setting is set for "wet", as that sounds like the type of batteries you have.

You could have one or more bad cells in your batteries.....might need to take them out and have them individually load tested.

Or it's possible the Xantrex is malfunctioning....a call to their tech support will probably guide you through more extensive troubleshooting.
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Old 08-09-2014, 07:51 AM   #9
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If you can charge the batteries OK with an external charger the problem is not the batteries. It really sounds like there is a charger problem. If you look at their site there is a remote panel available for that inverter/charger if you are interested and do not have it.

FWIW I have repaired stuff like that in the past. Usually it is not worth the cost of repair because the transformers get unstable. Replacing the fried active components gets them working but they fail under load. Most of the cost is in the transformer(s). Few places can test under load compared to the number that can do the simple get it working repair.
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Old 08-09-2014, 08:22 AM   #10
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If you can charge the batteries OK with an external charger the problem is not the batteries.

Very few automotive type chargers are 3 stage type chargers, designed to properly charge or maintain deep cycle batteries. So this is why I didn't put my faith in your statement. It's all too easy to simply connect one of these auto chargers, and think "....all is well .... " when it's not. Also depending upon the charger used, could have boiled water out of the batteries.
My only point is without more information, or testing, hard to rule out that the batteries aren't still part of the problem.
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Old 08-09-2014, 08:59 AM   #11
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I've got the 1500 watt version of the same inverter you have. When operating normally, it should indeed keep the voltage of your batteries above 13V.
While a battery charger should work, like other posters have said, it's going to have to be monitored. I've got a 35A charger in my workshop and it needs to be started each time it's used because it cuts off when it's done charging the batteries.

I think you have three options:

1. Replace the Xantrex 458 with a new one. This is the simplest solution and the easiest to install, which is probably worth some money right there... Also, no drop in RV value or functionality.

2. Remove the Inverter and replace it with an RV converter. A converter is a battery charger/house power supply that is the RV specific version of what you're suggesting. Don't cheap out, get one that has a three stage charger. This is probably the cheapest option, since a decent 45A converter ( like this one - Amazon.com: Progressive Dynamics (PD9245CV) 45 Amp Power Converter with Charge Wizard: Automotive ) is under $160. You will have to re-wire the 120V supply that went to your existing Inverter/Charger, though, since it passed through the power to some or all of your outlets in your RV. You will probably have to rewire some of the 12V wiring that went to Inverter, as well as remove the remote control panel for the old inverter.
This option will lower the value and functionality of your RV.

3. Replace the Xantrex with a better true sine wave inverter. Frankly, the 458's leave something to be desired with their power production and you can do better. Tripp-lite makes a 1000W unit that seems to retail for $700 and Magnum energy makes a 2000W unit ( you may need to upgrade the 12V wiring ) that doesn't seem to be much more expensive than a new replacement 458. Again, you'll have to change out the control panel, but that might be easy, depending on how it's wired.
This option will increase the value of your RV slightly and your electronics might be happier.

Just hooking up a battery charger is a janky solution that should only be used temporarily until you can fix the issue correctly.
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Old 08-10-2014, 10:06 AM   #12
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Very few automotive type chargers are 3 stage type chargers, designed to properly charge or maintain deep cycle batteries. So this is why I didn't put my faith in your statement. It's all too easy to simply connect one of these auto chargers, and think "....all is well .... " when it's not. Also depending upon the charger used, could have boiled water out of the batteries.
My only point is without more information, or testing, hard to rule out that the batteries aren't still part of the problem.
You do not understand 3 stage chargers. If the batteries come up to full charge with a single stage charger like an automotive charger the batteries are fine. All the problems you list will look like bad batteries not a bad charger. He said in the beginning that they batteries work with the single stage charger. The issue with single stage vs 3 stage chargers is that the single stage will in theory shorten battery life by not cutting back the charging current as the battery recharges then drop to a trickle to maintain when at or close to full charge. Reality is that most chargers are constant voltage so the charging current drops as the charge increases but they do not have a float mode so the will boil the batteries dry over time.

Another indication is that he can charge his battery bank with the single stage charger and use the unit for a day or whatever. If his charger was putting out rated current he would beed to be drawing 50 A from the charger plus significantly more current to bleed the batteries down while plugged in. If he is using something like 75 to 100 A when stopped and plugged in it's not the Xantrex but then he should know what is going on. He would also have a run time of a couple of hours on his battery pack with the single stage charger.

If he confesses he just put in a house style 120 VAC refrigerator on two 12V deep cycle batteries I'll buy that it is not the charger but unless he has done something like that his power usage should be what was there before and manageable for an overnight with the battery pack.

The basic issue always comes back to where is the power going. If he is running on AC his DC draw should be a couple of controller/sensor boards and a couple of lamp bulbs. Maybe 20 A? He is using well over 50 A if the Xantrex is working and the batteries are running down instead of charging.
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Old 08-10-2014, 10:39 AM   #13
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12v power supply for 12v systems

Quote:
My only point is without more information, or testing, hard to rule out that the batteries aren't still part of the problem.
I'm sticking to this, because I believe it's true. Maybe in the very beginning, the one stage charger was getting by.....

Quote:
Put new batteries in the coach last year but have been using an external battery charger to keep them charged.
So, apparently the OP said he has been running with the external charger for a YEAR now! In a YEARS time, it's very possible the batteries have been damaged.


Quote:
At present we have two 12v house batteries in parallel and still have 12v power weakness (voltage goes below 12v) after several hours with the "usual" neon lights operating.
This doesn't sound like good batteries to me. He says "below 12v" well, how far below 12?
We don't know. The Xantrex will shut off at 10v. I said in an earlier post the Xantrex very well be malfunctioning. But I don't believe the batteries are trustworthy at this point either (with the information at hand)
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Old 08-10-2014, 01:18 PM   #14
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A bit on 3 stage v/s 1 or 2 stage converter/chargers.

A single stage puts out a constant voltage, WITH good regulation that should be about 13.6 volts,, At this voltage a battery will never actually reach full charge,, But will get dang close (Say 95% or better) given time, lots and lots of time... OK if you are on a powered site most of the time and no power fails but.. If boondocking not so good.

Some single stage units are a tad lacking in voltage control and will boil your batteries dry in as little as 2 weeks (Magnetek mostly)

now, enter the multi-stage units.. Parallex 7300T is a 2 stage (The 7300 no T is a single with decent regulation).

This has a timed BOOST mode that puts out a slightly higher voltage to start charging faster... Useful if you have to re-charge with a generator as it cuts down on Genny run time.

And the 3 stage units (Too many to list)

These use both voltage and current regulation and sensing,, When you first "Plug 'em in" with batteries that are less than full they go into BOOST also called BULK mode. Very rapidly charging the batteries (IDeally around 30 percent of their 20 hour capacity) to around 90 percent.. Then the current drops like a rock as they continue to SLOWLY charge that last 10 percent... Then once the batteries are "Fat and happy" (Fully charged) they drop to float mode. (13.6) so as to maintain.

Some of them also offer equalization (A brief overcharge) and de-sulfication (Sometimes the same thing, sometimes advanced beyond this post) to improve battery life.

The Progressive Dynamics Wizard does a brief Overcharge (Equalization style) every 20 hours if in float mode. Takes about a year to "Boil the batteries dry" if properly sized.
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