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Converter/inverter idea


86rader

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My 87 Sunrader has the POS magnetek boat anchor. It no longer just cooks batteries, it has completely failed. I could use one of the more modern units, but I have a different idea. I have a number of APC Smart UPSes kicking around. I have been watching yt videos of folks that take these things, hook larger external batteries to them and use them as inverters. Seems to me that such a unit could serve dual purposes. It could work as an inverter when unplugged and a converter to keep the house batteries charged when plugged in. There is just one catch. The 750 uses a pair of 12VDC batteries in series for a total of 24VDC. This makes recharging the house batteries from the alternator a bit tricky. I was thinking that by adding a second inverter to make 120vac from the truck 12vdc, you could charge it that way. Of course such a system wouldn't be very efficient. Another issue would be tapping into that 24VDC bank for 12VDC. I guess you could set it up so that coach 12v system loads used one battery or the other.

Any thoughts?

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Well I don't know exactly what those APC things are but it looks like they cost way more than a regular RV power center. Wondering why your considering a less efficient system that costs more instead of the real deal.

Linda S

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Because I have a half dozen or so sitting in my basement.

These UPSes are used to power computers used on the TSA's xray systems. My day job, when I am not piddling around with old RVs is to maintain this equipment. For reasons that escape me, my company has decided to replace these UPSes when they fail rather than change the battery. Your tax dollars at work, I guess!

These small onboard batteries, (2) 7Ah 12VDC, are sufficient to keep these computers running long enough to power  themselves off. I have watched a number of YT videos where similar minded cheapskates have wired in a pair of deep cycle 12V batteries which will allow these units to run for extended periods.

I need to play around with this idea a little. It would be nice if these UPSes ran off a 12 V battery. Does anyone know of a more efficient way to achieve truck electrical system charging of a 24VDC battery than 12VDC>120VAC>24VDC via the UPS' charging system? And please don't say use a step up transformer as one youtuber claimed he was doing. Didn't even finish watching that video. About the only thing 12VDC can be transformed into with a transformer is smoke. I suspect he was using some sort of solid state DC converter and just figured it was a "transformer".

 

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On 5/26/2017 at 7:01 AM, 86rader said:

Because I have a half dozen or so sitting in my basement.

These UPSes are used to power computers used on the TSA's xray systems. My day job, when I am not piddling around with old RVs is to maintain this equipment. For reasons that escape me, my company has decided to replace these UPSes when they fail rather than change the battery. Your tax dollars at work, I guess!

These small onboard batteries, (2) 7Ah 12VDC, are sufficient to keep these computers running long enough to power  themselves off. I have watched a number of YT videos where similar minded cheapskates have wired in a pair of deep cycle 12V batteries which will allow these units to run for extended periods.

I need to play around with this idea a little. It would be nice if these UPSes ran off a 12 V battery. Does anyone know of a more efficient way to achieve truck electrical system charging of a 24VDC battery than 12VDC>120VAC>24VDC via the UPS' charging system? And please don't say use a step up transformer as one youtuber claimed he was doing. Didn't even finish watching that video. About the only thing 12VDC can be transformed into with a transformer is smoke. I suspect he was using some sort of solid state DC converter and just figured it was a "transformer".

 

Unless it's a pretty small UPS it probably is 24 volt (a pair of 12 volt 7 amp batteries series wired)  Yes it is true a transformer can not work on DC. To me it would be counter productive to dismantle an old UPS to make an inverter, a great deal of the electronics is devoted to charging and switching. Granted you can probably a good one at the dump more often than not they were thrown out because the batteries were bad.

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Picky point: Decades ago when studying for a ham radio license, I was taught that a transformer can pass DC IF the voltage is not constant, such as cycling between +3v and +15v.  It is true that if the voltage is CONSTANT which is usual for DC then a transformer cannot work.

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10 hours ago, BobBeery said:

Picky point: Decades ago when studying for a ham radio license, I was taught that a transformer can pass DC IF the voltage is not constant, such as cycling between +3v and +15v.  It is true that if the voltage is CONSTANT which is usual for DC then a transformer cannot work.

In order for it to work the DC would have to pass the zero voltage line (positive/negative) but if it does it 's no longer is DC. Case in point old DC generators were pulsed DC, + zero, + zero not + -. The frequency is not important but the wave has to drop below zero. Dropping below zero collapses the field in the transformer primary winding's making it pass to the secondary winding's. Many years ago there was a debate over power transmission (Edison vers Westinghouse) Westinghouse won because he produced AC voltage allowing the use of transformers to step up/step down voltages this allowed smaller wire and far longer distances eliminating the need to have dozens of generating sites when one would do for a large area. 

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Mmmm, so how does a ignition coil work?? 12v dc in and 35,000v dc out

I may be showing my antiquity but I remember old car radios. Vacuum tubes and they used a mechanical vibrator that feed pulsed DC to a transformer to make the various voltages to make the radio work. 

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Maineah, I am not certain, but I do believe simply changing voltage at a quick enough rate is sufficient to have it induce a current on the secondary. For instance, you could have a sinewave signal that varied from +5 to +20 on the primary and I do believe it would be seen on the secondary. If I remember my basic electrical theory, it is the change in voltage, that you need, not necessarily a change in direction. Of course, for practical purposes, we are talking about actual alternating current as that is what is produced by an alternator.

BTW, I saw your old Nova Star this past weekend. You left it in very capable hands. Larry and Joanie took what was already a pretty darn nice rig and made it into an absolute work of art. Didn't think you could make 30 year old fiberglass shine like that. I will be parked next to it at the Maine Toyin, I better get the buffer out so mine doesn't look too bad.

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If it is a sine wave it is AC. When you look at a AC wave form on a scope it goes from + to - not just + to zero if you look at a wave form from a DC source it is a flat line.    An Alternator is an AC generator it is 3 phase AC with 6 diodes to produce DC it uses DC to magnetize the rotating field by varying the field voltage you can regulate the output. WME's comment on a ign coil is a simple answer it is the field collapsing when the voltage is removed yes it will produce high voltage but it has to be turned on and off very much like an alternating wave form does. The same holds true for the old car radios vibrators they went from + to - to produce AC for the plate transformer. 

 Yes they have done a fantastic job with my old Nova Star did he tell you how he made the fiber glass shine? If not I'll spill the beans Zep floor wax 8 coats of it. Larry restores old tractors so he knows what he is doing.

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Yes, he did. A lot of work. He is a very talented guy. Have you seen the interior since Joanie's reupholstering job? Absolutely amazing. They make quite a team. Any chance you can make the Maine Toy In?

I am going to give it the Zep treatment after I finish getting years worth of mildew off. Larry did say, make sure it is absolutely clean because once you cover it with the zep, it is there for eternity.

 

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12 hours ago, 86rader said:

I am going to give it the Zep treatment after I finish getting years worth of mildew off. Larry did say, make sure it is absolutely clean because once you cover it with the Zep, it is there for eternity.

Obviously an exaggeration. What the Zep (and similar products) does is leave a 'skin' on the surface, sealing it AND any dirt/marks/defects in for all to see. If, after application, you decide you can't live with the flaw, you'll have to remove the 'skin' to get to what's underneath with a product like this:-

fbf6575c-58be-4424-a5fe-573cf655cfd9_100

http://www.homedepot.com/p/ZEP-128-oz-Heavy-Duty-Floor-Stripper-ZULFFS128/203144888

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10 hours ago, 86rader said:

Yes, he did. A lot of work. He is a very talented guy. Have you seen the interior since Joanie's reupholstering job? Absolutely amazing. They make quite a team. Any chance you can make the Maine Toy In?

I am going to give it the Zep treatment after I finish getting years worth of mildew off. Larry did say, make sure it is absolutely clean because once you cover it with the zep, it is there for eternity.

 

Yes I have seen her work I like the old jeans. Yeah I probably could when is it?

 

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Yes I concur on the Zep! I posted pictures of Grannie last year after the Zep treatment. Amazing! I only used 4 coats. Well worth the effort!!

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+2 for Zep. The first 2 coats won't look to good, #3 is better and # 4 starts to look good. I used 5 on the sides and 6 on the front. 6 starts to reach the point of diminishing returns.

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No idea. but mine made it through a harsh WY winter and looks great. 

Next year maybe just a recoat or 2. A full redo would involve using ZEP remover and then reapply the new ZEP. The major PIA of using ZEP is the prep work to use it the first time on a 20 year old RV, the redo should  :rolleyes: be easier.

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Mine also is holding up very well but only 1 year so far. When I took my rig in for under coating the guy asked me if I Zepped Grannie. He said his neighbor applied Zep to his RV and when he sold it 7 years later it still shined! I agree with WME,  it's a pain to prepare the surface but the results are Amazing!!

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