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Old 02-24-2011, 06:11 AM   #1
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1976 31' Sovereign
Springfield , South Carolina
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Posts: 213
Original AS Converter Question

76 Sovereign I got had original converter. PO told me the converter was shot and would not charge on board battery. Since the wall mount for it had collapsed and it was dropped down on the pump I pulled it out and tore out the original mounting which by no means was designed well enough to hold such a heavy unit.

I replaced it with a IOTA Power Converter/Charger and a Battery Minder and I could not be more pleased. Every time I walk in trailer I look at minder and it is sitting there at 13.4-13.7 volts warm or cold as I leave AS plugged into shore line all the time.

I have a buddy who is electronic tech have a look at old unit and he calls me and tells me he drilled out the rivets and started to check it out and found data on inside of unit it was 11.2V and this is exactly what it puts out. He explained in order to charge a battery the voltage must be slightly higher than battery is rated for which normally 13.5-13.8V and thusly a charger needs to be circa 15 volts. He also said the data on inside said it was a 70 amp unit.

I checked my small NAPA trickle charger I have on backhoe to keep up dual batteries and it is 15.2V and does nicely.

I was just wondering why AS did not install a higher volt unit so battery would charge? I guess I will just use this as a power supply for ham radio as this is useless for the AS. One thing for sure, it will not go back in as the IOTA is great and I have it mounted to a bulk head on other end of kitchen counter workspace up out of the way when I rebuilt underside of storage area and redecked it with 3/8" plywood and 2X2 reinforcing supported in middle by 2X4 pocket holed to deck in several places. I weigh 230 and now that shelf will hold me while I do push ups on it and doubled my undercounter space which now goes all the way to the hull wall.

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Old 02-24-2011, 08:30 AM   #2
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You may find that the output of the converter is not pure DC but rather a waveform that has peaks in excess of 13 volts.

As a result, it will actually charge the battery, even though a meter will show a lower voltage.

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Old 02-24-2011, 09:10 AM   #3
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Yes, and a converter that old will probably have bad filter capacitors, causing the problem that Jammer discribes.

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Old 02-24-2011, 12:09 PM   #4
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It may not have filter caps at all. If it is the type with an SCR there are no capacitors. Typically the secondary of the transformer in the univolt is 19 volts peak to peak, when rectified by the full wave bridge. 19 volts AC peak to peak will produce about 13.4 volts of unfiltered DC. 19 x .707 = 13.4. When you calculate the .3 volt drop if the diodes a germanium or .7 volts if the diodes are silicon you are looking at between 12.7 and 13.1 volts DC peak. The unfiltered output of the rectifier will look like mmmmm. Picture all of the M's as a string of half circles all strung together. If there are filter capacitors the output will be smoothed out and look like -------.
However the voltage will be lower than the peaks in the full wave DC, the capacitors tend to smooth out the peaks and valleys in the unfiltered DC, thus the average is lower than the peaks and higher than the valleys.
The univolt would have to put out 21 volts on the secondary of the transformer to produce a DC charge voltage of 14.6 volts; typical of the charge circuit in your TV.
If the univolts primary to secondary voltage ratio is 120/19 that's a 6.31 to 1.
If the input voltage is 110 volts not 120 volts the secondary output of the transformer would be lower by about 9 %. Resulting in an even lower charge voltage.
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Old 02-25-2011, 04:22 AM   #5
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1976 31' Sovereign
Springfield , South Carolina
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Does anyone have a schematic for the AS converter? The data he found on inside said 11.2V which is what is has.

The only other change I made was place the IOTA on the bedroom bulkhead and got new wire to make the long run ( 5FT?) and it does charge the battery just fine.

My buddy has a couple of discharged car batts and he hooked it up to them to see if it would do better under load but haven't got a report on that yet.
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