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malconium 04-23-2007 01:15 PM

Probably not the original converter?
I am restoring a 1973 31' Airstream and I am starting to put the electrical system back together. I have generally been thinking that I would need to buy a new converter. I thought I would take a closer look at the one that was in the unit when I bought it because I had a vague recollection that it did not look like the original. Looking more closely I found that it did not seem to fit the original space and that it had an old price tag on it. So it seems like it was replaced somewhere along the line.

The converter-charger is a Magnetek model TU-750-6 and the price tag said that it sold for $205.66 when it was new. So I have a few questions that I would like some help with:

1.) How old would this unit be anyway?

2.) Is this a good product - if it is still working properly?

3.) How do I tell if it still works properly? I could easily enough hook it up and test the voltage at the output side. It says, though, that it has built in overload protection but how could I tell that the overload feature is still working?

4.) Is this something that a qualified RV shop can do a thorough check on?

5.) Should I add anything in the way of a charge protection gadget to this type of unit? If so specifically what gadget?



Wabbiteer 04-23-2007 03:10 PM

There should be a date code printed in same ink on exterior shell case - My Airstream was man'f 9/72 and its' converted is stamped 05 72...

Technology has vastly improved. Intelli-power makes a nice unit...

malconium 04-24-2007 09:30 PM

Basically I am trying to find out how much newer than the original converter the after market unit that is in my Airstream is. I also need to know if it is working and whether or not it would be an OK unit to use at least for the time being. The price tag was over $200 and I don't want to toss it arbitrarily.

I checked with a large RV repair shop near me to see what they would charge to test the unit if I bring it in. They told me that their service charge is $94 per hour an that there is a 1/2 hour minimum. That means it would cost me $47 to have them put the thing on the tester and give me an assessment. Somehow that seems pretty steep to me. I can understand that part of the charge has to go toward paying for the equipment but how long could it take to hook up a converter and read off the results? I am guessing that a really slow technician would take maybe 10 minutes. As I indicated in my earlier post I do have a volt meter that I could attach myself to see if it is putting out the voltage. What I am uncertain about how to check is the overload circuitry or the functionality of any filtering circuits.

So I have a few more questions:

1.) Does anyone have any simple checks that I could do myself?

2.) Are testers for checking this sort of thing expensive?

3.) Is there anything that I can add to the charging circuitry if I use this converter that would help stabalize and filter the power?



Wabbiteer 04-25-2007 01:30 AM

You haven't found a date code?

The uni-volt requires a battery load to complete filtering circuit - don't run it w/o one, the transformer can be damaged and it is cumulative; you don't know history and a few minutes could make for a interesting moment.

Best way to check is add battery and watch the battery voltage - I believe the owners manual has specs. IIRC it outputs 18VAC for that works out to 12VDC for utilities; There are three capacitors that might be oversized but retail on them could be harsh. I strongly recommend you get rid of the uni-volt, it wastes alot of power and is hard on batteries...

lewster 04-25-2007 07:20 AM


IMHO, regardless of whether the unit operates to spec or not, you still have an older unit with no charge control. By that, I mean 3-stage automatic battery charging. This is a must to maintain your batteries properly for long battery life and proper charging. The Univolts and other converters of their era can cook a battery if left on indefinitely.

A new 3-stage converter will 'read' the battery voltage and alter the charging voltages as needed to protect your battery and maintain them at their peak charge level with no overcharging.

They are well worth the money in saved batteries!:D

overlander63 04-25-2007 07:41 AM

If you don't want to pay the "big bucks" for a brand new Intellipower (although they are very good), maybe you could find a new take-out from a late model Airstream or SOB. It would be a fraction of what a brand-new unit would cost, and much better than what you have. I got one for our coach from a forums member that had upgraded his, and it has worked flawlessly. In fact, you may be able to check with your friendly RV service techs (like the one above) to see if they have any take-outs you could acquire.

Wabbiteer 04-25-2007 09:22 AM

1 Attachment(s)
Ferro-resonance transformer definition per Wikipedia :

"By arranging particular magnetic properties of a transformer core, and installing a resonant tank circuit (a capacitor and an additional winding), a transformer can be arranged to automatically keep the secondary winding voltage constant regardless (within some limits) of any variance in the primary supply without additional circuitry or manual adjustment. CVA transformers run hotter than standard power transformers, for the regulating action is dependent on core saturation, which reduces efficiency somewhat."

Don't let the combined design of the unit hold a place for it in your trailer.

It is easy and desireable to salvage the 12 volt distribution panel off the unit for re-use as the fuse panels contruction is HEAVY DUTY and almost irreplaceable in todays market. I used a rotary aluminum oxide abrasive disk to slice through the sheet metal cover-frame assembly to keep it stock; I have a Blue Sea Systems 12V panel that will eventually replace the uni-volt fuse panel but am saving the electrical as finishing touches to the rehab...

Wabbiteer 04-25-2007 10:07 AM

Additional Wikipedianese:


".. the transformer typically gives off a lot of heat, these units are typically large, bulky, and inefficient."

"While this used to be the dominant type of UPS, they are no longer used for common applications. Power factor correcting equipment found in newer computer systems interacts with the transformer, causing potentially damaging oscillations, and the transformer itself can create distortions which yield power less acceptable than poor quality line AC. These units are still used in some industrial settings, but have mostly disappeared from use with general computer equipment."
Yet more reasons to donate the transformer to the local salvage yard...

lewster 04-25-2007 08:08 PM

That's why all of the F/R converters required a battery as a filter........and they STILL didn't work well!:lol:

malconium 04-25-2007 08:18 PM

Somehow I must not have asked part of my question adequately so let me try again...

The converter that I have is obviously not the original one for the reasons I stated. So we are not talking about replacing an original 1973 vintage converter which I agree would be a good idea if that was what I actually had.

The unit may or may not be an old one and that is part of what I am asking about. How do I tell whether the one that I do have is ancient technology or perhaps that I have lucked out and have a reasonable model that would be fine for my needs?

Can anyone ihelp me dentify the manufacturers model that I listed in my first post in this thread and help me determine whether or not it might be worth keeping? The part number is not a current product number for Magnetek so I so far have not able to find it listed when I searched for it on the Internet.



malconium 04-25-2007 08:26 PM

What is the best choice for a new one?
So if I do decide that I need to replace my current converter what is the best choice for my age of unit? It currently has a 30 amp power system. How about some recommended model numbers and recomendations as to where to buy one?



lewster 04-25-2007 08:30 PM

A 55 amp will do nicely. I replaced the Progressive Dinamics unit that was stock in my '06 19CCD with a WFCO with 3-stage battery charging. A FORUM member, 68 Overlander, is in this business. Give Randy a PM and he'll answer all of your questions. Nice guy too! BestConverter - Inteli-Power Converters, Inverters, Solar Chargers :D

Excella CM 04-25-2007 09:11 PM

The fact that is labeled "magnetek" is reason enough to toss it.

Pacerized 04-26-2007 12:39 AM

I just ordered the Parallax 4455tc. I originally was going to go with the intelicharger, or WFCO, but went with Randy's advise on the Parallex. I think you'd be better off with any of the 3 starting at around $179. The Parallex has more charging stages, and adjust based on battery temperature from a sensor cable. The other 3 stage chargers change output based on a timer. It seemed to be worth the difference in price to me.
If you've checked the output of the univolt with a multi meter, and it works you could just stick with it. I did last year, but decided to upgrade this year after overcharging one of my batteries which I think I'll have to replace.

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