UHaul Converter - Peering Inside - Fiberglass RV


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Old 09-21-2012, 02:37 PM   #1
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UHaul Converter - Peering Inside

Let me preface this discussion by stating that I'm a mechanical engineer and any errors made are from ignorance, as opposed to malice.

I've wondered if I should replace my old converter on my CT UHaul. I rarely camp with electricity, so I am curious to see how much of a battery boiler this converter is. Today I decided to take it apart and see what is inside.

It appears that it has a split output when plugged in. One circuit isolates the battery and charges it and one circuit powers all the trailer accessories off the transformer's DC output, independent of the battery.

With no battery connected, the charging circuit output is 12.44 volts and the accessories circuit is at 13.47 volts.

With a small jumper pack battery connected at 12.8 v, the charging circuit jumps up to 14.24 volts and the accessory circuit remains fairly steady at 13.41 volts.

Given that a fully charged battery is about 12.7 volts, I would think that the charger circuit output should be closer to a float voltage, like 13.4 volts. There is a small electronic circuit board that appears to regulate charging voltage (circa 1985).

Any thoughts or insight from those of you with more experience?
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IMG_3849.JPG   IMG_3848.JPG  

IMG_3852.JPG   IMG_3854.JPG  

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Old 09-21-2012, 03:39 PM   #2
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I would just go to some place like WallyWorld and purchase one of those batteries that has a 3 year free replacement warranty the not worry about boiling it.
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Old 09-21-2012, 04:13 PM   #3
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Tom, I'm not a BSEE and would look foolish playing one here, but here are the three levels of charging voltage of a Progressive Dynamics "smart" charger (PD 9245) with which I replaced the converter end of my Newmark electrical sevice.

Assuming a discharge to 12.4V level, "Boost" (desulfation mode) charges at 14.4V and takes the battery to 90% of full charge in roughly four hrs. "Normal" mode kicks in at 13.6V for another 30+ hrs. at which time the charging current is reduced to the 13.2V of "Storage" (float) and maintained until battery use and discharge triggers "Normal" mode once more. In addition, there is an "equalization" mode which provides 14.4V for 15 minutes at 21 hr. intervals. My multimeter consistently gives me readings .06V under the stated current for each stage which suggests that PD's specs are accurate. The 14.2 voltage reading which you are getting is very close to the agitation or desulfation level for the PD which would make a layman such as myself think that the converter is probably an electrolyte boiler. This seems to be the going skinny on "older" converters.

FYI, I wired with 6awg welding cable to battery (17' run) and to distribution panel from split bolt taps on the main line (about 18"). The contactor on the original rig which presumably handled the "isolation" of outputs is not needed w/ the PD9245.

jack
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Old 09-21-2012, 04:17 PM   #4
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I kept the fuse panel and threw away the rest of it. To answer the original question: I have no idea how it really works, mine seemed to kill the battery rather than charge it. I just installed a PD 4045 converter but have not tried it yet. Before that I was just using an 1150 truck battery and recharging it with a 10 amp automotive charger. The truck battery is staying in place. For our 3 month snowbird trip this winter most everywhere has electric, but the camper was out 3 weeks this summer with no electric available and the battery never went dead being used for lights only.
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Old 09-21-2012, 04:45 PM   #5
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Thanks for the replies thus far.

Right now I'm thinking that I may just add a toggle switch to over ride the charging when it is plugged in.

All accessories will be running off the converter and if the battery is low, I can flip the switch to let it charge.

If the battery is charged (off the solar panel), I can just let the converter run the accessories and leave the battery isolated.

I don't have much confidence that the electronic circuit shown in the photo above is adequate to protect the battery.

Incidentally I was dreading unbolting it from the floor, but someone (bless their hearts) attached it with stainless steel bolts, which just threaded out.
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Old 09-21-2012, 05:09 PM   #6
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Bob, I thought the 4045 was a combination distribution panel/converter. Did you have room for that and the old fuse panel. The 9245 is converter only but was an easy bolton to the case of the Newmark.

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Old 09-21-2012, 05:58 PM   #7
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http://www.appliedgmc.com/images/PD9200_Manual.pdf

Wiring schematic for PD 9245. No isolation of charge function from power function that I can see there. Batt and fuse panel are in parallel. Hard for me to believe it's that simple but there it is!

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Old 09-22-2012, 02:03 PM   #8
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Just to finish this thread - I decided to replace the jumper wire between the charger terminal and the battery terminal in the charger with a toggle switch.

I rarely camp with electricity, but when I do, I can just flip the switch and let the DC converter power the trailer without worrying about the battery boiling.

The solar panel generally keeps the battery topped off nicely. Should I need to charge the battery off 110 volts, I can flip the switch back to the charge position.

If I decide to upgrade in the future, it will be easy to install an intelligent charger / converter in place of the current converter, though I think I'd move it up under the furnace and run heavy wires back to a fuse panel mounted in the same area as the converter is now.
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Old 09-25-2012, 11:31 PM   #9
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Reading this (pretty much indecipherable) discussion illustrates to me, just what men must be hearing when women are in a deep discussion about Tulle, Toile, or Crinolines, and whether taupe cushions will go better with cerulean or salmon curtains..... Women really are from venus!
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Old 09-26-2012, 05:48 AM   #10
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No kidding! By Tom's final post I too was suffering from vererean strabismus. It's all about complementarity, nuts and their bolts.

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Old 09-26-2012, 07:23 AM   #11
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Quote:
Originally Posted by Pam Garlow View Post
Reading this (pretty much indecipherable) discussion illustrates to me, just what men must be hearing when women are in a deep discussion about Tulle, Toile, or Crinolines, and whether taupe cushions will go better with cerulean or salmon curtains..... Women really are from venus!
Pam, what I said (in Male Martian), was that I'm too cheap to install a modern converter.
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Old 09-26-2012, 08:10 AM   #12
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The parsimonious solution to the single charge rate battery boiling converter is monitoring and an off switch. Works for me.

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Old 01-14-2013, 04:30 PM   #13
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Tom,

I don't currently have a battery installed. (The one I was going to use ended up being toast.) I will be getting one soon hopefully. I was reading all the manuals and looking at the wiring diagrams and have pulled out the 120v outlet box in mine trying to see how it's all wired together.

One thing that isn't clear to me, does the 120v outlet work at all when just running off the battery? (I know if I had a battery this would be answered in about 2 secs.) It doesn't look like to me from the wiring diagrams that the converter would do this.

PO had wired a 120v mini Fridge directly into the 120v outlet and I'm assuming that the fridge won't work without it being plugged into shore power. (which I guess means taking a cooler on a long road trip)
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Old 01-14-2013, 05:17 PM   #14
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Quote:
Originally Posted by knighth001 View Post
Tom,

I don't currently have a battery installed. (The one I was going to use ended up being toast.) I will be getting one soon hopefully. I was reading all the manuals and looking at the wiring diagrams and have pulled out the 120v outlet box in mine trying to see how it's all wired together.
I'm assuming you still have the 110 volt cord that pulls out the door on the left side.

Quote:
One thing that isn't clear to me, does the 120v outlet work at all when just running off the battery? (I know if I had a battery this would be answered in about 2 secs.) It doesn't look like to me from the wiring diagrams that the converter would do this.
No, when you are not plugged in, all you have is 12 volts (or so) off the battery (when you install it).

Quote:
PO had wired a 120v mini Fridge directly into the 120v outlet and I'm assuming that the fridge won't work without it being plugged into shore power. (which I guess means taking a cooler on a long road trip)
I think you've got it right. You could put contained ice in the refrigerator and use it as an ice box

By the way, I decided to leap into the 21st century and bought a smart charger, which I'll replace the above dissected box with.

http://www.ebay.com/itm/Inteli-power...4967c4&vxp=mtr
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