12V Power Supply for 12V Systems

[mel s]

Originally Posted by JJH3rd

Boondocking 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)

JJH3rd
Where are you going to get the 120VAC to run a "beefy AC->12VDC power supply"?
If you have 120VAC shore or genset power just run the 120VAC systems with that, like the rest of us.
Mel
'96 Safari

[pasdad1]

Originally Posted by mel s

JJH3rd
Where are you going to get the 120VAC to run a "beefy AC->12VDC power supply"?
If you have 120VAC shore or genset power just run the 120VAC systems with that, like the rest of us.
Mel
'96 Safari

I believe the OP intent was to say, if he always has shore power or generator, why does he have to worry about the upkeep of a battery to power all the 12 volt items in RV.

If it were wired this way, then the coach owner would have to use a flashlight to see in the coach at night while driving, or anytime the generator wasn't running.....but I suspect most people wouldn't put up with that limitation, which is why I've never seen one wired that way.

[JJH3rd]

More fuel for the fire:

Xantrex tech said that I should see 13v -> 14v accross the batteries if the charger functioin is working. I will check tomorrow and post the results.

Thanks for the links to alternatives.

[JJH3rd]

Notes from the "field"

OK I got out to the MH with my multimeter & here's what I found.

1) the ground cable to one of the two batteries was so loose that I could pull it off by hand. This means that "probably" I've only had one of the two 12v batteries supplying power to the MH. This is a good answer to the question "Why did the voltage drop and lights dim after just an hour or so?"

2)
.........Xantrex | Battery
-------------------------------------------------
.............13.5v | 12.5v
-------------------------------------------------
.Positive post | Negative Post | 13.5v
-------------------------------------------------
Negative Post | Positive post | 12.5v

The Xantrex battery charge light is on.

The voltage across the 12v terminals on the Xantrex is 13.5v.
The voltage across the battery is 12.5v (it had been on charger for half hour & went from 10.5 to 12.5v)
The voltage from the Xantex positive post to the battery's negative post is 13.5v.
The voltage from the Xantrex negative post to the Battery's positive post is 12.5v

So...

My current plan of action is to

1) fix the battery terminal for the negative post for the 2nd battery and see if it will hold a charge > 12v.

2) track down, & replace if necessary the cable from the Xantrex positive post to the battery's positive post.

BTW the battery charger is an old (+30 years) Schauer 10 amp tractor & truck charger (big, heavy transformer) that is a multi stage charger (at least two) that can be (& has been) used to maintain the charge on batteries.

[pasdad1]

Originally Posted by JJH3rd

BTW the battery charger is an old (+30 years) Schauer 10 amp tractor & truck charger (big, heavy transformer) that is a multi stage charger (at least two) that can be (& has been) used to maintain the charge on batteries.

What makes you think it's a multi-stage charger? Chargers from that era were only 1 stage, either fixed current, or more likely, fixed voltage.....you see the amp meter move from 10 amps towards zero as the battery charges, only because as the voltage in the battery increases, less current can be "pushed in" by the charger. Using this type of charger long term will boil the batteries.....not good :(

[BFlinn181]

You mentioned the battery, "had been on charger for half hour & went from 10.5 to 12.5v" What you measured was a 'surface charge' before the electrons had been absorbed into the lead plates. To get an accurate measure on state of charge, after disconnecting the charger the battery needs to 'rest' for at least 3 hours to level out the charge.

[JJH3rd]

Evening of the first day report:

It looks like the battery with the loose connection has a dead cell.

I found the voltage drop in the positive line - its the DC fuse. It "shouldn't" drop more that tiny fraction of a volt but right now there's a 1 volt differential across it. I've got a replacement on the way.

I got out the wire brush and a box of baking soda and really cleaned and "freshened up" the post and lugs the fit together at that point.

I'm charging that battery overnight and will see if it will hold a charge after it rests.

So the outstanding question right now is do I have one or two bad batteries?

More to come.

[bukzin]

Originally Posted by JJH3rd

Evening of the first day report:

It looks like the battery with the loose connection has a dead cell.

I found the voltage drop in the positive line - its the DC fuse. It "shouldn't" drop more that tiny fraction of a volt but right now there's a 1 volt differential across it. I've got a replacement on the way.

I got out the wire brush and a box of baking soda and really cleaned and "freshened up" the post and lugs the fit together at that point.

I'm charging that battery overnight and will see if it will hold a charge after it rests.

So the outstanding question right now is do I have one or two bad batteries?

More to come.

Many battery shops will load test your batts for free. If bad you can get
a little credit towards new ones.

My local shop also installs for free.

Costco also sell good batteries and good prices.

[JJH3rd]

Remember my voltage measurements table:
.........Xantrex | Battery
-------------------------------------------------
.............13.5v | 12.5v
-------------------------------------------------
.Positive post | Negative Post | 13.5v
-------------------------------------------------
Negative Post | Positive post | 12.5v

I found that the voltage going into the 200Amp fuse between the Xantrex and the house batteries was 1 volt higher than what came out the other side of the fuse. I ordered a new fuse and in the meantime used some #10 wire to "jumper" across the fuse holder. I now see "no" voltage loss between the Xanterx and the house battery.

I will get a new battery from Camping World next week because the one that failed is less that 18 months old.

SO... When I replace the 200Amp "T" fuse, I expect to see no voltage drop which will mean that the Xantrex "should" be able to keep both house batteries fully charged.

Sidebar -

The box of LED replacement lights arrived today. My plan is to replace the "most used" incandescent and florescent lights with LEDs. That should really help the battery drain (as well as finding I had a resistor instead of a fuse in the battery charging circuit).