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Old 10-29-2008, 05:46 PM   #1
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Need electrical system expert advice

I’ve got some strange electrical issues that I’m hoping you electrical experts can help me with- or at least give me some ideas that I can raise with J/C…

We’re talking about a new 2008, that I took possession of in late 2007.

Dead, and quickly drained batteries (while boondocking) had me thinking there was a problem right off - but I couldn’t be sure, since the coach was being used 90% of the time plugged into 30A shore power…. and it seemed to perform OK on shore power… (except when it melted the head of the power cable at a campground utility box- I chalked that up to a bad electrical service)

So after freshly charged batteries had gone dead, while sitting in my driveway overnight- I decided to install a Trimetric 2020, and attempt to identify if, and on what circuit, there might be a short… and also get a better idea of what was happening charge-wise.

Got around to installing the 2020, along with a 100A shunt. The distribution bar next to the charger/converter had only one ~4AWG black wire… so I tapped that for the shunt… and on the opposite distribution bar, I connected the Trimetrics fused positive wire to the stud that connected to the coverters + hookup (Bogart tech support said that should be OK, although they recommend going directly to the battery stud)

Readings on the 2020 look respectable:
-.05 kill switch ‘off’
-1.60 water pump cycling
-4.80 furnace fan blowing
-11.70 all interior lights

At the time I installed the 2020- The trailer was winterized, and in storage- I didn’t have any shore power… plugged the chevy burb in at the umbilical cord, and idled the engine…

This is where it gets interesting

The 2020 showed -.09A and 12.9V no charge.
Checked the burbs 7-way, showed ~14V (the P3 brake controller also showed ~14.00V)

Let idle for about five minutes.. no change in Trimetric reading.

Then- while I’m scratching my head, staring at the Trimetric, my helper ‘accidentally’ hits the brakes in the burb, activating the actibrake hydraulic pump in the trailer—suddenly the amp readout jumps from -.09 to 1.12 and shows charge

After a couple of minutes, the amps drop to -.19 (we’re still hooked up, with burb idling)

We repeated this sequence (hitting brakes, showing charge… then a few minutes later showing a drain) several times


Sorry for the lengthy post.. any help would be greatly appreciated...

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Old 10-29-2008, 06:46 PM   #2
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Joe,

Intriguing. Are you using the Suburban battery to power the Actibrake, or did you wire it to the trailer battery?
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Old 10-29-2008, 06:55 PM   #3
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Originally Posted by markdoane View Post
Joe,

Intriguing. Are you using the Suburban battery to power the Actibrake, or did you wire it to the trailer battery?
hey mark,
it's gotta be wired to the trailer batts... when I bled the brakes (on the a/s), I could cycle the pump by pulling the breakaway switch- and that was disconnected from the burb
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Old 10-29-2008, 07:10 PM   #4
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My conjecture

Your dead batteries could be the result of bad batteries or a big parasitic load you have not yet found. Disconnect the batteries and see if they discharge on their own.

Your converter might have stepped up it's charging activity when your assistant hit the brakes because the increase in current caused by every single brake light coming on AND the brake controller powering the brakes caused a momentary voltage drop in the charge line which fooled the converter into thinking it needed to come on to combat a power hog.

Even though the surge was brief, the converter might have been programmed to stay on the job to make sure everything was okay.

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Old 10-29-2008, 07:22 PM   #5
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Your dead batteries could be the result of bad batteries or a big parasitic load you have not yet found. Disconnect the batteries and see if they discharge on their own.

Tom
Tom,

but wouldn't any parasitic draw show on the 2020?
would that kind of behavior, by the converter, indicate a bad unit?

Joe
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Old 10-29-2008, 07:24 PM   #6
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hey mark,
it's gotta be wired to the trailer batts... when I bled the brakes (on the a/s), I could cycle the pump by pulling the breakaway switch- and that was disconnected from the burb
It has to be wired to the trailer battery for the breakaway function to work, but the instruction sheet says the primary power connection is to the tow vehicle.

Is it possible that the relay on the actibrake is causing power from the tow vehicle to try to charge the battery, when the brakes are activated?
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Old 10-29-2008, 07:31 PM   #7
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Originally Posted by markdoane View Post
It has to be wired to the trailer battery for the breakaway function to work, but the instruction sheet says the primary power connection is to the tow vehicle.

Is it possible that the relay on the actibrake is causing power from the tow vehicle to try to charge the battery, when the brakes are activated?

like if the brake control wire was shorted with the power wire in the tow vehicle harness or umbilical?
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Old 10-29-2008, 07:58 PM   #8
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No, I don't think it would be a short.

I think the Actibrake has two sources of power to the pump. It may have a relay that takes power from the tow vehicle if the umbilical is connected, and if the umbilical is disconnected is takes power from the trailer battery.

I'm kinda shooting in the dark here. I'm guessing the main power source is the tow vehicle because it uses a #12 wire, and the back-up breakaway power is only a #16 wire.

I'm sure it's a lot more complex than I imagine, but if the blue wire tells the pump to turn on, it might close the power relay and send 14 volts from the tow vehicle to the trailer battery.

I also think Tom is on the right track thinking that the power flow from the tow vehicle needs to exceed some threshold value before the power comes on.
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Old 10-29-2008, 09:41 PM   #9
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http://www.airforums.com/forums/f439...g-30369-2.html

this post could answer be the answer to your problem, caused from the electric to hydrolic pump, lots of reading.
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Old 10-29-2008, 10:02 PM   #10
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Perhaps another datapoint: put a meter across your positive bus and negative bus, and compare with the trimetric reading. Repeat with umbilical connected.

Do the readings match with the trimetric?

Cheers,
-jd.
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Old 10-29-2008, 10:36 PM   #11
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Don't know about the later models but when the breakaway is pulled power to the brakes is from the trailer battery and when the brakes are applied power comes from the TV brake controller.

I suspect you need to verify the battery (charge line) from the TV is connected to pin #4 of the 7 way connector (black 10 gage wire) and the #4 pin on the Airstream side goes to the battery this sounds like a miss wiring on one end.

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Old 10-29-2008, 11:31 PM   #12
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possible?

Hi, sounds like another one of the wonderful G.M. tow vehicles connected to an Airstream with disc brakes sindrome. Check for the dummy fuse [instead of a real fuse] that G.M. uses in their fuse panel that is needed for the charge wire in your seven pin connector. Seems that this has become a common problem with this set up.
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Old 10-30-2008, 06:21 AM   #13
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Quote:
Originally Posted by letsgo123 View Post
http://www.airforums.com/forums/f439...g-30369-2.html

this post could answer be the answer to your problem, caused from the electric to hydrolic pump, lots of reading.
whew... just read
looks like after much aggravation, it turns out to be a missing AUX/POWER underhood fuse?

the fuse is definitely in, and I'm reading +14V at the suburbans 7-way...

</electrically challenged newbie thinking out-load> it's simply a bad actibrake controller... 'soaking' up any charge from the suburban?
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Old 10-30-2008, 06:27 AM   #14
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Don't know about the later models but when the breakaway is pulled power to the brakes is from the trailer battery and when the brakes are applied power comes from the TV brake controller.

I suspect you need to verify the battery (charge line) from the TV is connected to pin #4 of the 7 way connector (black 10 gage wire) and the #4 pin on the Airstream side goes to the battery this sounds like a miss wiring on one end.

Garry
what position is 4 on the a/s umbilical?
my suburban 7-way is giving me +14v at the '2' and '7' o'clock positions... (alignment notch at '12')
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Old 10-30-2008, 08:13 AM   #15
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the 12+ and ground are reversed on my tow vehicle vs. the airstream owners manual
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Old 10-30-2008, 08:43 AM   #16
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Try this for the connector pin out


Marksrv.com 7 way wiring diagram page

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Old 10-30-2008, 09:28 AM   #17
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the 12+ and ground are reversed on my tow vehicle vs. the airstream owners manual
If that's the case, it would certainly draw down the coach (and tv) batteries fast, pretty much a dead short.
I just scanned through this thread without reading it all, but have you unplugged the umbilical, and checked to make sure the + and - match on both truck and trailer through the connection?
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Old 10-30-2008, 09:56 AM   #18
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Quote:
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Let idle for about five minutes.. no change in Trimetric reading.

Then- while I’m scratching my head, staring at the Trimetric, my helper ‘accidentally’ hits the brakes in the burb, activating the actibrake hydraulic pump in the trailer—suddenly the amp readout jumps from -.09 to 1.12 and shows charge

After a couple of minutes, the amps drop to -.19 (we’re still hooked up, with burb idling)

We repeated this sequence (hitting brakes, showing charge… then a few minutes later showing a drain) several times


Sorry for the lengthy post.. any help would be greatly appreciated...
Would like to mention that Airstream changed the wiring in July 2008.

"New Style Hydraulic Braking Pump - Active Technologies has eliminated the need to run the vehicle charge line through the pumps circuitry. Airstream now wires the charge line to the house batteries through the bus bar located on the interior of the unit."

Would not explain the batteries in your trailer running down, but would explain why you only had charge when the brakes were applied.
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Old 11-01-2008, 11:41 AM   #19
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Verified wiring.
Contrary to my last post, the +12v, ground, ‘blue’ feed, all wired properly…
Neat- I’m trying to reconcile your post with what the actibrake wiring diagram shows… not sure I understand…

Reconnected suburban to trailer… but this time I followed the ‘recalibration’ procedure (as outlined in a/s and actibrake manual), which entails holding the manual brake lever to ‘max’ for 5 sec, after each time you connect umbilical…

Trimetric reads ~1.2A charge
Every two minutes or so, the Trimetric will show the charge drop into a -.07 draw for just a second or two, then immediately swing back to around a 0.6A charge… climbing slowly… until it dropped back to a draw, and repeated the cycle…
I monitored this behavior for about ten minutes while I idled the truck

I also noticed, that when I pushed on my truck brake to activate the trailer brakes, the Trimetric would register a –1.3A draw, while the pump was cycling…
So essentially, instead of getting a fresh charge while logging my 10 hours of travel, I’m slowly draining the trailer batteries… unless of course, I don’t use my brakes…


Regardless of whether this 'yo-yo' charging effect is normal... is an amp-and-a-half all I can expect to get through my trailer/truck umbilical?

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Old 11-01-2008, 06:35 PM   #20
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Joe,

Intriguing. Are you using the Suburban battery to power the Actibrake, or did you wire it to the trailer battery?
The actibrake should be wired to both. TV when attached and house when not.
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