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Old 02-15-2008, 08:55 AM   #1
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Univolt Replacement

I have a 1973 29 ft Ambassador that I am replacing the Univolt with a 9200 Inteli-Power and new fues box. The old Univolt is under the stove just above the battery box. This is where all of the cables/wires come out of the floor and wall. Is this the normal place for the Univolt? I plan to build a platform for the Inteli-Power and fuse box. I have a bunch of wires to reconnect.
Thanks for any advice.
TShep
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Old 02-15-2008, 09:04 AM   #2
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The normal place for the univolt is basically wherever Airstream decided to put it in a particular model. If yours is directly above the battery box, that's great. That will mean less large wires to go to the battery. When you take the Univolt out, don't throw it away until you remove the fuse panel, you will need it for the new unit. If you don't have a switch for the converter, it would be a good idea to wire one in so you can turn it off at will.
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Old 02-15-2008, 09:32 AM   #3
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Battery wire guage

When you wire the batteries, do not fall for the common falicy that the wire has to look like starter wires in a car. A starter motor can draw 700 amps--you will never draw that under any circumstance in a trailer. You can fuse your batteries at 25 or 40 amps, depending on your loads (pumps, lights, fans, stereo) and wire accordingly. Generally speaking, #10 wire is big enough to go from the battery to the fuse block. You may have momentary surges that approach the limit from things like a tongue jack, but these are very short duration. I dare say #12 is big enough (with a 25 amp fuse), but the safety Nazis will poo-poo that, so I use either #10 or #8, whatever's handy.

The worst current situation is when the trailer battery is completely dead. There will be a high in-rush current for a few seconds, but this quickly comes back to less than 40 amps. Besides, your converter will shut down if the load exceeds its output capability. The ony other source of current would be the charge line from the tow vehicle, but it's usually fused with a thermal fuse which will reset periodically (you'll hear it clicking on and off until the intial charge has gotten to the point where the charge current is "low"). Make sure you have this thermal fuse between the tow vehicle charge line and the trailer--if you don't have any fuse, you can damage the wiring in the trailer and tow vehicle, if you have a melting type fuse, you'll never get a dead trailer battery charged (from the two vehicle).

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Old 02-15-2008, 09:35 AM   #4
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Nice choice on a converter/charger. You will need a DC distribution panel of some sort. I am currently changing out all of my ac/dc and converter. What I am using is an IOTA on the DC an AC side. You can find these here. IDP-12 DC Distribution Panel from IOTA Engineering
They have a very nice look, and are simple to install. Nice upgrade from the old tube fuses. The fuses have more contact area and are easier to find anywhere. The 12v housing also has red leds that light up if a fuse blows.
You can order online from various dealers. If you want to go that route, let me know and I can order one for you. (we do rv parts)

I don't really know why you would need a switch for the converter. It only works when connected to shore power and is used to supply 12v for battery charging and the 12v appliances. It is as simple to just unplug it if ever needed for replacement or maintance.

Zep is the man. Ditto on his advice also. Another tip. Don't reverse the positive and negitave leads. This is bad for some converters. But the 9200 you would only have to replace the fuse.

Good luck!
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Old 02-16-2008, 09:43 AM   #5
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Smile Hi All,

Well I finaly instaled my intel charger with a monitor. What a joy. No more 60 cycle hum and when the charger it is off the batterys are not hot anymore.
My instalation was simple becouse the fuze block was not on the univolt. It is mounted on the wall behind the couch.
Does anyone know what the third black wire is for on the univolt. I think it is for the indicator when it is hooked up to shore power but what is the voltage output? If anyone has a shematic for control panel for 1985 Sov. Please send it to me.
Regards from Russell In cloudy and cool Tucson Az.
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Old 02-16-2008, 12:58 PM   #6
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Changed my converter and used a simple fuse panel from West Marine, had to add in line fuses for ckts over 30 amps, the panel rating. Works great and I got rid of the glass fuses.
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Old 02-16-2008, 01:09 PM   #7
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Quote:
Originally Posted by RUSSELL
...
Does anyone know what the third black wire is for on the univolt. I think it is for the indicator when it is hooked up to shore power but what is the voltage output? ...
I believe you are correct about the purpose of the wire. Mine was 12 volts.

There is a control panel schematic here for 1975. It might be similar.
http://www.airforums.com/forums/f37/...ams-38170.html

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Old 02-16-2008, 03:41 PM   #8
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Smile Hi Zep,

Thanks for the info. and shematics. Will try to hook up 12 volts and see if the shore power indicator works.
Regards fromm Russsell in sunny and warm Tucson Az.
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Old 02-16-2008, 06:47 PM   #9
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Tshep. That is likely where the original univolt was. I've seen it there on many models. I know it was there on my 76.
The wire between the battery and fuse board needs to be at least 8 AWG and preferable 6. Zep made a safety comment and rather than get into that, just assume that 60 Amps will travel that wire and it very well might. A 25 amp fuse is not big enough either.
Performance is also important because of the voltage drop. Under rated cable will cause the converter to see a lower voltage and the automatic mode change of the converter will be affected. I've seen it a thousand times on units with the Intel-Power, WFCO and others. Manufactures are usually responsible because they skimp on wire size to save money. The consumer is left with the crappy performance.
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Old 02-16-2008, 11:17 PM   #10
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This is a very interesting discussion. Here's a semi-official table of copper wire characteristics from the Web (these are continuous ratings):

AWG Ohms Current Fusing
1000ft Carrying Current
4 0.2533 59.6 -
6 0.4028 37.5 668
8 0.6405 23.6 472
10 1.018 14.8 333
12 1.619 9.3 235


Household codes specify that #12 wire can be fused at 20 amps. What's going on here? At 20 amps, 1 foot of #12 wire would dissipate (using the old school favorite, P =I squared R) 0.64 watts. Yes, you could feel it get warm....a little. The 9.3 amperage is conservative, to say the least. That's about 0.14 watts per foot. If you're familiar with 1/4 watt carbon resistors, they're about 0.15" in diameter and 0.3" long. They get hot, but they don't melt.

If you look at your individual circuits in Vintage Airstreams, they are #14 stranded wire and are fused at 15 amps. The tow vehicle charge line is fused with a thermal automatically reseting breaker at 25 amps--yes, I have occasionally observed this fuse clicking off and on, especially when using the electric tongue jack with no battery in the trailer. I offer this as one data point about maximum currents.

If you consider voltage drop rather than maximum current/thermal issues, then it's wire length that matters. Let's take a Sovereign, at 28' of shell length, you might have 40' of wire between the battery and converter (worst case, devices at opposite ends, same side, but wire run is on the other side). At 50 amps in a #10 wire over 40' you'd lose 2 volts. That's bad bad bad. But at 25 amps for 4' (a more representative case, I think), it's 0.1 volts, which is more representative of typical maximums. The first case is obviously unacceptable for a 3-mode converter like all the of the modern ones, but the second case is perfectly acceptable.

I think you have to make your design fit your situation. If you've got long wire runs between the battery(ies) and your converter and if you have 40 or 60 amp converters, then you need big wire. But typical installations don't need to blindly opt for the worst case, biggest wire scenario.

It's a matter of philosophy--if you go for the big wire and the big fuses, you'll be safe and you'll never blow a fuse unless something goes wrong. If you go for moderate sized wire and appropriately smaller fuses, you may blow a main fuse once in a blue moon, even if nothing is wrong. But either approach is safe.

I go for the smaller fuse scenario (and smaller wires, usually) because it gives me an early indication of problems. If I blow one battery fuse and not the other, it might be telling me that I've got a bad cell or a battery imbalance problem. etc. My opinion is that big fuses only tell you that you dropped your screwdriver across some exposed terminal and ground (which I have done more than once). Not real helpful.

Is the real answer "big wire, small fuses?" You decide.

Maybe this is a discussion that reflects a boon docking attitude versus the always-gotta-be-plugged-in-and-if-I'm-not-I've-got-an-1100-Watt-inverter attitude. Hoo Boy, now we're talkin' 100 amps...

Don't have a clue... Peace.

Zep

PS--did I get my math right, Mr Charles Shaw?
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Old 02-16-2008, 11:28 PM   #11
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There are several places to figure your wire size for amps/volts/length/etc and will give you your figures to make sure your in range for NEC standards. I am including a link for one of them. Or you can get your calculator out and do the math. The link below will allow you to enter the voltage your working with and other considerations. Good wiring to all.

American Wire Gauge table and AWG Electrical Current Load Limits
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Old 02-17-2008, 01:06 AM   #12
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I like the lead-in pargraph to the table. I also like the chassis amp limit--it provides a good idea of what a short run wire should be able to carry. Thanks, very helpful.

And yes, good wiring to all.

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Old 02-17-2008, 03:04 AM   #13
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Are we talking about AC or DC? I was refering to the original post and am clearly off topic if it changed from DC to AC. Household and DC have not so much in common.
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Old 02-17-2008, 09:32 AM   #14
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Quote:
Originally Posted by 68 Overlander
Are we talking about AC or DC? I was refering to the original post and am clearly off topic if it changed from DC to AC. Household and DC have not so much in common.
Electrons don't know if they are coming from an AC or DC source. The wire size will be determined by the voltage, Amps, and length of cable. You will have more voltage drop the longer the cable is. The problem comes when you have to long of a cable that is not sized right. Then the amps increase and you have heat, when it reaches a certain point, it melts and BOOM, or fire.

You can put any voltage thru any wire, but you can not put any amperage thru any wire. For instance, telephone wire is 24 gage and you pump an average of 48 volts thru it and have spikes up to 120 volts for ring voltage but the amps are very low milliamps. Same thing with your water pump in your RV. It is 12 volts, and draws 5-7 amps thru that 14 gage wire, everything is fine.

Your problem comes when the demand for amps (either AC or DC) is greater than the wire will carry. Then you blow a fuse or melt down.

When you figure wire gage, current type does not matter. Your amperage is the key. The wire you work with should be rated at 600 volts and 70 degrees C. You need to know your amps and length to size properly.

Also, someone said that the 60 amp converter could pull 60 amps. I have a lot of DC stuff, but don't think I can total 60 amp draw with everything on unless I have a short or massive voltage drop.

Hey guys, are we getting off topic? Should we start another wiring post?
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