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Old 06-25-2015, 01:18 PM   #1
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Voltage from the 7-Pin?

Who here has measured the 12V from their 7-pin trailer connector?

My dad and I were talking about some potential battery problems I may or may not be having (kind of a long story, but the punchline is I'm not sure my battery is charging correctly) and he asked a question I hadn't considered: "Did you measure the 12V from the 7-Pin?" Well, of course not, why would I do that? SMH

So last night I grabbed my trusty volt meter and a map of the pins and went to measure the 12V lead (the one designed to charge your battery under way) and found it to be 14.4 volts. Truck was started and running at idle.

This threw me for a bit of a loop; I expected it to measure about 13.2 or so.

So how many of you have measured yours? What are/were your readings?
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Old 06-25-2015, 01:55 PM   #2
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14.4 at the battery on a running engine means a perfectly functioning charging system.


I would also expect that when the RV's charger is in "Bulk Charge" mode.
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Old 06-25-2015, 01:58 PM   #3
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Want real fun?


Connect an un-damped analog meter directly to the output of the alternator.


Watch the needle flick and rock!
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Old 06-25-2015, 02:05 PM   #4
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Quote:
Originally Posted by mike837go View Post
14.4 at the battery on a running engine means a perfectly functioning charging system.


I would also expect that when the RV's charger is in "Bulk Charge" mode.
Not at the battery on the truck, this is measured on pins 1 & 4 at the bumper of the truck. I went in and checked the DIC in the truck's instrument panel, and it said 14V (no tenths on that gauge, and yes it is a numerical readout, not the "idiot light" type). I always assumed it would be around 13.2 (trickle charge) at the bumper; I haven't had the opportunity to check if the 12V at the 7-pin is correlated to the vehicle's on-board battery charging voltage...

Note: the voltage as measured at the battery terminals on my trailer with the charger in "bulk" mode is 14.2; output from the charger at that stage is supposed to be 14.4 according to the manual.
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Old 06-25-2015, 02:16 PM   #5
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Quote:
Originally Posted by Camper_bob View Post
Who here has measured the 12V from their 7-pin trailer connector?

My dad and I were talking about some potential battery problems I may or may not be having (kind of a long story, but the punchline is I'm not sure my battery is charging correctly) and he asked a question I hadn't considered: "Did you measure the 12V from the 7-Pin?" Well, of course not, why would I do that? SMH

So last night I grabbed my trusty volt meter and a map of the pins and went to measure the 12V lead (the one designed to charge your battery under way) and found it to be 14.4 volts. Truck was started and running at idle.

This threw me for a bit of a loop; I expected it to measure about 13.2 or so.

So how many of you have measured yours? What are/were your readings?
Your truck charging system is working just fine.

have you checked the specific gravity in you battery? Make sure you battery is full of electrolyte (top off with battery acid, not distilled water), charge overnight, then check each cell's specific gravity (the meters, and battery acid can be bought at any auto parts store).
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Old 06-25-2015, 02:18 PM   #6
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Originally Posted by Camper_bob View Post
Not at the battery on the truck, this is measured on pins 1 & 4 at the bumper of the truck. I went in and checked the DIC in the truck's instrument panel, and it said 14V (no tenths on that gauge, and yes it is a numerical readout, not the "idiot light" type). I always assumed it would be around 13.2 (trickle charge) at the bumper; I haven't had the opportunity to check if the 12V at the 7-pin is correlated to the vehicle's on-board battery charging voltage...

Note: the voltage as measured at the battery terminals on my trailer with the charger in "bulk" mode is 14.2; output from the charger at that stage is supposed to be 14.4 according to the manual.
1) You'll have to dig into some serious technical manuals to find out if the manufacturer decided to send a trickle charge to the breakaway battery or just threw a resistor in the line to protect the truck's electrics. If it is just a resistor, you will get full electrical system voltage when there is no load.

2) The factory instrument panel in any mass produced car/truck/van/suv etc. is inherently suspect. If it is accurate, it will show 14V when your DVM shows 13.5 to 14.4. Also the instrument panel is reading the voltage behind the dash somewhere.

3) If the RV has been on shore power for more than a day, the converter will have switched to float mode and dropped to a trickle charge.

Overall, don't worry about any differences under .5 of a volt. Temperature changes in the batteries and the components of the charging systems will give you that.
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Old 06-25-2015, 02:37 PM   #7
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Originally Posted by tjpolsin View Post
Your truck charging system is working just fine.

have you checked the specific gravity in you battery? Make sure you battery is full of electrolyte (top off with battery acid, not distilled water), charge overnight, then check each cell's specific gravity (the meters, and battery acid can be bought at any auto parts store).
Haven't gotten that far yet. So, here's why I'm doing all this:

DW said the battery was "dead" when she was trying to set the stab jacks in the driveway after a trip. It was the only time she did anything involving the trailer the whole weekend without me being present (I was inside napping with my son

So I don't know what exactly happened, and I couldn't replicate the problem she described. She is not very technical at all, and so diagnosing a problem based on her description of what happened (especially with her assumptions about what is causing the problem) is dodgy at best!

The trailer had sat in the driveway for approximately 3 hours hooked up to the truck after a 2.5 hr drive home. The only item running in the trailer on top of the typical drain items was the fridge. So the battery should have had plenty of juice to run the jacks.

The only time the trailer is off shore power is when it is being towed down the road connected to the truck. The battery comes home with me while the trailer is in storage and is stored on a float charger in my garage that has been repeatedly verified to be putting out 13.2V. I have always topped off the cells with distilled water since I have owned it (never takes much since it doesn't get enough voltage for "boil off"). My first test was the charge controller in the trailer and it seems to be working perfectly (voltage tested normal at all three stages of charge at the terminals on the battery), so the only thing left to check from a charging standpoint was the truck. I have verified to my satisfaction that the truck is putting out the proper voltage (I guess 14.4 is not abnormal?).

So now I'm left with only 2 conclusions that I know of: 1) DW isn't describing a dead battery, but another problem that has nothing to do with the battery or 2) I have a bad cell in the battery and/or it's not holding a charge.

I can check to see if it's holding a charge at home because it's in the garage. I'll just take it off the float charger when I get home from work and put the volt meter on it after dinner (I know it's not a load test, but it's all I've got right now). I don't know when I'll get a chance to acquire a specific gravity tester or battery acid. I don't even know if they're needed at this point...
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Old 06-25-2015, 02:52 PM   #8
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"So I don't know what exactly happened, and I couldn't replicate the problem she described. She is not very technical at all, and so diagnosing a problem based on her description of what happened (especially with her assumptions about what is causing the problem) is dodgy at best!"


Stop trying to find a problem that may not exist.


It's possible that the fridge killed the battery in the hour or two between getting home and plugging in?


I'm trained as an electronics technician and I am currently a systems admin and applications programmer for a single office.


1st rule of fixing a problem: Have the customer demonstrate the problem!
Otherwise you are chasing your tail.


My life is filled with non-technical folk (Mom, SWMBO, all but 1 of my coworkers, not so much with my dad, but he turned 84 this year...) and I make sure I see what is going on.


Programs fail all the time. Me: "What was the error message?" Coworker "I dunno, I hit enter to clear it". When I check the logs, the user tried 4 time and got the same message.


When SHMBO has a problem with the TV or cable box I just have to get both ON at the same time.


So, the best you can do is got to the DW and say "Honey, I know you had a problem. But I can't seem to find it. Next time, show me what you are doing and then I'll be able to tell how the RV didn't work." At no time blame her for not operating something properly. She could have pressed the wrong button, you have no idea.


Blame the RV. But next time the stabilizers have to be deployed/retracted, watch how she does it. That may reveal what went wrong before.
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Old 06-25-2015, 04:38 PM   #9
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Quote:
Originally Posted by mike837go View Post
"So I don't know what exactly happened, and I couldn't replicate the problem she described. She is not very technical at all, and so diagnosing a problem based on her description of what happened (especially with her assumptions about what is causing the problem) is dodgy at best!"


Stop trying to find a problem that may not exist.


It's possible that the fridge killed the battery in the hour or two between getting home and plugging in?


I'm trained as an electronics technician and I am currently a systems admin and applications programmer for a single office.


1st rule of fixing a problem: Have the customer demonstrate the problem!
Otherwise you are chasing your tail.


My life is filled with non-technical folk (Mom, SWMBO, all but 1 of my coworkers, not so much with my dad, but he turned 84 this year...) and I make sure I see what is going on.


Programs fail all the time. Me: "What was the error message?" Coworker "I dunno, I hit enter to clear it". When I check the logs, the user tried 4 time and got the same message.


When SHMBO has a problem with the TV or cable box I just have to get both ON at the same time.


So, the best you can do is got to the DW and say "Honey, I know you had a problem. But I can't seem to find it. Next time, show me what you are doing and then I'll be able to tell how the RV didn't work." At no time blame her for not operating something properly. She could have pressed the wrong button, you have no idea.


Blame the RV. But next time the stabilizers have to be deployed/retracted, watch how she does it. That may reveal what went wrong before.
I guess it's possible the fridge killed the battery, but not plausible. 12V only runs the electronics, so not much draw there. I forgot that the antenna booster was also on at the time, but I would still expect the battery to last more than 2-3 hours even with that and more being powered up in the camper.

You're absolutely right; I have no interest in chasing my tail. And 9/10, she can demonstrate the problem. But so far I'm not out anything. I tested the things that were easy to test and were my first "suspects", if the problem was as she described (and honestly these should be checked periodically anyway; if nothing else, I've learned a thing or two). I have only yet to test the holding ability of the battery before I give up and chalk it up to "Ok honey, I'll take a look next time it happens".

I know WAY better than to "blame" DW for these things, even if it IS her fault, and she knows when I'm patronizing her and doesn't stand for that either. LOL!

Can't wait to get out there again!
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Old 06-25-2015, 08:02 PM   #10
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Better luck next time when the intermittent problem shows itself again.

Enjoy more camping and your family!
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