12V Power Supply Install...Quirky Voltage Readings--FIXED

RZRBUG

Some time ago, I installed a cut-off switch for my battery that's mounted on top of the battery holder lid.  Since I have no power supply on the outside of my trailer, I decided to install a 12V power supply on the front of the LP/battery housing.  I first connected the 12V power supply leads to the same posts that the battery cables were connected to at the cut-off switch.  When I turned the switch on, power came on to the T@B, but there was no power to the 12V power supply.  I don't understand that, but it was no problem, really, as I disconnected the leads of the 12V supply from the cut-off switch and connected them directly to the battery terminals.  Bingo, power to the 12V supply.  I checked this by plugging in the digital voltage meter that has the 12V (cigarette lighter plug) on it.  The voltage read 12.5V.  That reading is a little low, so I hooked up to shore power to top off the battery.

Now for the quirky part.  After letting the battery charge a while, I again checked the reading on the voltage meter, and it still read 12.5V.  I then took the voltage meter inside the trailer and plugged it into the 12V supply there and got a reading of 13.6V, which is about the maximum charge for the battery.  I then took the meter back to the power supply I had just installed and plugged it in.  The reading was 12.5V.  So, I turned the battery disconnect switch to "On," and the voltage reading on the meter jumped to 13.6V.

Since the wires to the new power supply were now connected directly to the battery terminals, why should it make any difference on whether the battery cut-off switch is on or off?  And which is the correct reading, the 12.5V or the 13.6V?

Verna

13.6V if you're plugged into shore power...at least that's what I've always had.  This is the voltage coming to the 12V sockets from the converter.

The 12.5V is what the actual voltage is from the battery without any external source connected (making an assumption based on the voltage from my current and the previous battery in my Silver Shadow). 

Did you still have the shore power connected, Larry when you were getting the 13.6V with the battery disconnect switch set to on?

I'm just going by what I get on my battery.  13.6V if I have shore power connected, 13.0V if I have the trickle charger connected to the battery, and a max of 13.0V if the meter is plugged into the 12V socket in the galley, without any external power source connected to the battery.  

RZRBUG

Thanks, Verna.  Yes, shore power was connected when I got the higher reading.  Influence of the converter sort of makes sense, now that I think about it, but it sure threw me for a loop when it happened.  I have since gone back and checked the voltage both inside (old power supply) and outside (new power supply) with no shore power connected and they both read 12.5V.  I had wrongly assumed, I guess, that the battery had actually charged to 13.6V when I checked it previously with shore power connected, but that apparently is not the case.  Truthfully, that doesn't make since either as it is a 12V battery.  The maximum battery charge then is somewhere around 12.5V without shore power connected?

BTW, you (and Mike) will be happy to know that the ARB has been ordered.  We all knew that would be the end result, didn't we?

Verna

You'll love the ARB, Larry!! No more yucky icy cooler water!!! Oh, and in splicing a new quick disconnect last night, I did find the ARB wiring is 8 gauge. That should help with your shopping for suitable wiring for your socket.

In answer to your question, it seems strange, but the 12V battery can be charged up to around 13V. I checked mine last night before I answered you. 13.0V with the Battery Tender Jr plugged into it, and 13.0 if I unplugged the Battery Tender Jr. The only thing plugged in is the meter in the galley...I'm not sure if the converter takes a bit of the charge away every day....The battery is a new 100 ah AGM
battery and it loses the charge very slowly if not connected to the trickle charger.

Michigan_Mike

Technically speaking Larry, the electric converter converts the 120 VAC 60 Hz from the outlet to 120 VDC after it passes through Diode Rectifier #1, the Capacitor then filters the ripple voltage. This 120 VDC voltage is then fed to an Electronic Switching Circuit that converts it back to AC and increases the frequency from the original 60 Hz to 3,500 HZ. This high frequency AC voltage is then fed to a step-down transformer where the output voltage is reduced to approximately 13.6 volts AC and Diode Rectifier #2 converts the AC to 13.6 Volts DC and the Capacitor filters out the ripple.   >:)

You're gonna love that ARB too!   

DurangoTaB

Verna...why did you choose a 100Ah AGM battery (and what brand)? I'm thinking of replacing our (brand new) wimpy 56Ah wet acid battery for boondocking.

Verna

DurangoTaB said:

Verna...why did you choose a 100Ah AGM battery (and what brand)? I'm thinking of replacing our (brand new) wimpy 56Ah wet acid battery for boondocking.

JD, my neighbor is a mechanic, and a service writer, and says that he feels the best battery is the Interstate brand of battery.  So, I talked to the guy at Interstate and got the prices from him for 75, 100 and 150 ah AGM batteries.  (I only had a 35 ah AGM battery in mine.)  Then on the Teardrop Radio show with John from Zamp Solar, I asked him what size would be appropriate for the 80 watt Zamp Solar Panel that I had.  He said that anything over 100 ah would be overkill for the 80 watt Solar Panel.  So, he saved me $50 and I went with the 100 ah, not the 150 ah.  As far as the AGM, that is for an inside location, such as my galley where my battery is located under the counter.  You can save yourself some more money if your battery is located on the tongue of your T@B, because the AGM is more expensive, and is unnecessary if located "outside". 

Does that help?

Lisa33

Both Verna and Mike give great info. I think I just read that Interstate makes the Costco batteries. Might be worth checking out if you're a member. The 12v "full charge" numbers have always been confusing to me, too. 12.5 is indeed a full charge, but that reading can vary based on lots of factors including whether it is under load or not (something running off of it like a light or the refridge, etc), ambient air temperature and whether it has been very recently charged (inflated number called a surface charge). I wish it were more straightforward, but it just isn't. Over time you get a feel for it in your own circumstances, but it can be confusing for sure! Lisa

DurangoTaB

Thanks Verna! Most helpful...and I also have the 80watt Zamp solar panel, currently ;-) hooked up in our bright sun and charging at about 2-3amps.

Verna

It used to be confusing to me, too, Lisa, until I had to verify the operation of "48V" battery strings in the telephone company central offices.  When you added up the voltage for the string of batteries, it was 52.8V DC, and it had to be within a few tenths of a volt within that or you had to perform more tests.  So, yes, there can be variations between batteries filled with the same amount of liquid sitting right next to each other, manufactured at the same factory, in the same month and year. 

And, yes, I've gotten used to what my battery reads, and I do a double take if there is just one tenth of a variation. 

With the knowledge that I gained, I know now that the original battery in my SS was actually dead when I got her.  It had been sitting at the factory unused and uncharged for at least 18 months when my dealer got it.  It measured 10.5V when I got it home.  Sure it charged up to 13.0V on the battery charger, but I never really trusted that battery for more than a few hours.  I knew that I had to get a new battery for all of the boondocking I hope to do (you know, the "save my money" type of camping!!) I hope to do out west this summer and this winter.

RZRBUG

So, the quirky voltage readings weren't so quirky after all.  I have a camping friend who is a retired electrical engineer, and I'm sure he could have explained all of this to me, but his explanations usually shoot over my head as soon as he opens his mouth. )  I worked for the same company he did for years as a communications specialist, and I was always struggling to translate his technical jargon into common English.

The good thing is that apparently everything is pretty much normal.  Now if the new 12V power supply will just run the ARB...

Oh, one other question:  When I fuse the ARB, should the fuse be installed before the 12V supply, or between the 12V supply and the battery?

Verna

Larry, I'm not sure what your 12V power supply is.  Do you have a link?

But, without knowing exactly what it is, I would put the fuse at the battery to protect that investment. 

RZRBUG

Verna, I don't think I understand your question.  The 12V supply (cigarette lighter type plug in) is wired directly to the trailer battery.  I plan to plug the ARB directly into it with the cord supplied with the ARB.  What do you mean by "link"?

Verna

OK, Larry...I call that the "12V socket".  I thought you had a different type of 12V apparatus that you were using and I didn't understand, so I wanted a "link" to where you bought it so I could see a picture of what you were talking about.

Soooo, I understand you now!!!

OK, put the fuse as near to the battery positive side (+ side) as you can.  I have less than 12" of wiring between the fuse and the battery positive side.  I'm using the same type of quick disconnect plug that is used for the 80W Zamp Solar Panel or for the Battery Tender (they use the same type of quick disconnect plugs).

RZRBUG

OK.  Thanks.  I already have a fuse assembly ready to be wired in.  I will do that before I plug in the ARB and test it out.  It's supposed to be here Thursday.  I have some of the quick disconnects that you mention, but the "socket" seemed to be easier to anchor to the cover.

RZRBUG

OK, it's back to the drawing board.  The ARB came today, and of course, I tested it out immediately.  It works fine in the house and works fine plugged into the 12V socket inside the T@B.  It won't do anything plugged into the 12V socket I installed on the battery/LP cover.  This outside socket has the same voltage reading as the inside one, 12.5V when not hooked up to the TV, 13.8V when hooked to the TV with the motor running.

Now, what do I do?

Michigan_Mike

Flip the wires around on the battery/LP cover and see if that helps......  There's no reason it shouldn't work and the ground wire is obviously in the wrong position.   I had the same issue when I hooked up a cigarette lighter receptacle to the extension cord for my ARB as white is normally "always'' the ground wire, but mine was probably made in China.   

That should do the trick!  

RZRBUG

Thanks for the info, Mike.  That could be the problem, but I have ordered an ARB branded wiring harness that they make specifically to run the refrigerator.  It is supposed to be labeled as to neg and pos to prevent such mistakes.  The wiring is larger and is engineered to prevent voltage drops.  I will wait until it arrives and install, then see what happens.  Should have done that to start with, I suppose.  Will let you know how that turns out.

Verna

Larry, what gauge of wiring did you use for your homemade harness?  Just curious. 

Lisa33

I'm thinking along the same lines as Verna. Perhaps the gauge of the wire is insufficient. I had (minor) problems with using 12v extension cords for that reason. ARB recommends 10 gauge wire.

Verna

I was hoping to use a "Y" 12V socket on the rear of the console in the Escape.  Nope, it wouldn't work.  It's gauge was too small and wouldn't power up the ARB.

RZRBUG

You guys probably hit the nail on the head.  I used 12 gauge wire, but the run was only 12-15 inches, so I did not think there would be much voltage drop in that short of a run.  The socket I installed, however, probably had 14 gauge, and I cut the wires pretty short to the socket before splicing.  It was not labeled, but just by looking at it, I'm thinking that is probably what it was, and it may have even been 16.  I have a gadget I could have measured it with, but didn't.  I'm pretty confident that the wiring harness I have ordered will do the trick since the refrigerator operates on the socket already installed inside the T@B, and the new harness is made by ARB specifically for the refrigerator.  If it doesn't work, I'll be back jumping up and down...but not very high. )

RZRBUG

The new socket and wiring made by ARB came today.  I installed it, plugged the refrigerator in, turned it on, and.....BINGO.  Started right up.  The new socket is not the cigarette lighter type, but a special one made by ARB.  So, I still don't have an outside power source, but I can take care of that later.  Important thing is that the ARB is working.

I did discover that one of the screws holding down the battery/LP cover had stripped, but that will be an easy fix.  No cracks nor splits in the cover.  As my dear Mom is want to say, "It's always something."

Michigan_Mike

I cut off the socket that came with the ARB extension cord and spliced on an exterior, marine grade cigarette style receptacle on mine and it works fine.  Glad things worked out Larry and agree, there is always something to fix and repair but that's what make life interesting.  

Verna

So glad it's working, Larry.  Now for no soggy cooler food, and no more looking for ice every day.

RZRBUG

Happy, Happy, Happy. )

I plan to install the socket that wouldn't work for the ARB for an auxiliary 12V outside power supply.  Don't know what I'll need if for, but I already have it made up and it will be there if I ever need it.