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Old 06-28-2022, 07:05 PM   #1
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120 volt to 12 volt converter

I have and intellpower 9100 model pd9145a Which is a 45 amp @725 watt converter 105-130 input output 13.6vdc I found on Amazon the only converter close is a Recpro that's 45 amps but it's only 650 watts but they have a 55 amp @800 watts my question would the 55 amp @800 watts be to much for my 2003 Fleetwood storm motorhome
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Old 06-28-2022, 07:57 PM   #2
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Wiring size is the issue...not the watts

45A ---- probably 8ga used

55A ---- should be 6ga
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Old 06-28-2022, 08:00 PM   #3
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Ok thanks
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Old 06-29-2022, 04:08 AM   #4
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Originally Posted by Gary2220 View Post
,,, my question would the 55 amp @800 watts be to much for my 2003 Fleetwood storm motorhome
No it would not. The listed numbers are the capacity of the converter to support demands which would be the DC devices installed in your coach plus what the batteries would demand during recharge. Going with a slightly larger capacity hurts nothing but your budget if the cost is higher than the original.

If you want to stick with a 45 amp model - https://www.amazon.com/Progressive-D...s%2C131&sr=8-5. I'm on year 10 with a 9200 Series 60 amp model which is a few dollars less than a 45 amp.
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Old 06-29-2022, 06:24 AM   #5
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You need more information to know for sure if 55A is "too much".

Batteries have a charge current rating, for flooded like GC2's it's typically 13% of the rated Ah, so assuming 220Ah is 28.6A. So even a 45A converter would be overcharging a pair of GC2's in some circumstances. If it's 4 GC2's the max charge rate would be 57.2A, so then a 55A converter would be "just right".

It can be reasonably assumed that if the converter is charging the batteries, there will be other loads present which divert some of the charge current. So in those cases, even a converter that's "too big" may be "just right" when simultaneously charging and operating loads.

Most people don't pay attention to battery charge rates and go with the notion that "more is better" and will merrily cram as many amps into them as possible to speed up charging. This works for the bulk part of the charge phase but the absorb phase is a function of time and won't change, so the total charge time will be reduced but not by a huge percentage. The damage to the battery is cumulative, so charging hard "once in a while" you're probably OK but if it's done every single cycle hundreds of times and at high currents, battery service life will diminish.

The supply cable can impact peak charge current significantly. So even if you install a 55A converter it won't supply 55A if the supply cable gauge is small, or there's a long run. In that case it doesn't really hurt anything other than you bought a bigger converter that won't perform any better than a smaller one.

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Old 06-29-2022, 07:32 AM   #6
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You need more information to know for sure if 55A is "too much".

Batteries have a charge current rating, for flooded like GC2's it's typically 13% of the rated Ah, so assuming 220Ah is 28.6A. So even a 45A converter would be overcharging a pair of GC2's in some circumstances. If it's 4 GC2's the max charge rate would be 57.2A, so then a 55A converter would be "just right".

It can be reasonably assumed that if the converter is charging the batteries, there will be other loads present which divert some of the charge current. So in those cases, even a converter that's "too big" may be "just right" when simultaneously charging and operating loads.

Most people don't pay attention to battery charge rates and go with the notion that "more is better" and will merrily cram as many amps into them as possible to speed up charging. This works for the bulk part of the charge phase but the absorb phase is a function of time and won't change, so the total charge time will be reduced but not by a huge percentage. The damage to the battery is cumulative, so charging hard "once in a while" you're probably OK but if it's done every single cycle hundreds of times and at high currents, battery service life will diminish.

The supply cable can impact peak charge current significantly. So even if you install a 55A converter it won't supply 55A if the supply cable gauge is small, or there's a long run. In that case it doesn't really hurt anything other than you bought a bigger converter that won't perform any better than a smaller one.

Mark B.
Albuquerque, NM
Charge current into a battery is determined by the internal resistance of the battery (along with any resistance in the length of the cable and connection points) and the applied voltage from the charger. For a given voltage, only a certain amount of current will flow. If the setup, considering the factors mentioned above will allow 30 amps of current to flow, it would not matter if the charger has the capability to provide 45 amps, 75 amps, 100 amps or any number above the 30 amp number....it simply does not matter. I = current E = voltage R = resistance. Therefore, I is equal to "E" divided by "R".

Look at it like this.....You have a 120 volt light bulb rated at 100W being fed from a 15 amp breaker in the breaker panel. The wattage of 100 will cause .833 amps to flow. Then you decide to feed that same 100W, 120 volt light from a breaker that is capable of providing 20 amps. Do you think the light will pull more current just because the source is capable of providing more amps.....or will the current remain the same as the original .833 amps?
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Old 06-30-2022, 07:42 AM   #7
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If the setup, considering the factors mentioned above will allow 30 amps of current to flow, it would not matter if the charger has the capability to provide 45 amps, 75 amps, 100 amps or any number above the 30 amp number....it simply does not matter. I = current E = voltage R = resistance. Therefore, I is equal to "E" divided by "R".
True, but what if the factors allow higher currents to flow? Batteries do have internal resistance but it's not constant, based on the size, type, state of charge and integrity of the battery. The external conditions are fixed but the battery is a variable. If one measures a given setup over all operating conditions and indeed the battery impedance sets the rate, then I agree a larger converter won't force more charge current. But until you do measure it, system impedance can't be assumed.

My RV has a pair of costco GC2's and a 45A rated converter. Into "dead" batteries I have measured sustained currents of 45A plus for well over an hour. So it's definitely possible a "typical" setup could hit the current limit rate of the converter.

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Old 06-30-2022, 09:43 AM   #8
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Old-Biscuit has given the best answer. Trust him. It is as simple as that.

You have a 40 amp converter and it is enough for you. You need a least a 40 amp converter to replace it.

There is no problem with increasing the capacity of the replacement converter except for the 12 volt positive and negative wire size from the converter to the battery and to the fuse panel.

A higher capacity converter may charge your battery bank faster. Larger battery banks can absorb more current if it is available.

Higher capacity converters need larger 12 volt cables and fuse.

The Intelli-Power is a precision converter/charger line up. They will not harm your batteries or damage 12 volt equipment.
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Old 06-30-2022, 09:51 AM   #9
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A 650 watt converter would draw 5.5 amps at 120 volts.
A 800 watt converter would draw 6.6 amps at 120 volts.
The 120 volt circuit breaker supplying 120 volts to your converter in your RV would be at least 15 amps.

The small difference is not significant for the 120 volt supply.
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Old 06-30-2022, 12:14 PM   #10
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All the advice above is technically correct but seems to me to be excessively cautious for this simple situation. The upgraded charger isn't going to overwhelm your battery(s) - it will let the batteries take current (amps) at whatever rate it is comfortable with (absorption charging). And the 55A rating is combined 12v house supply + charging - it's not force feeding 55A to the batteries all the time. I see no practical problem at all with this upgrade.


That said, I see a couple of 45A converter/chargers on Amazon, including the excellent Progressive Dynamics 9245. Granted the PD is more $$ than Recpro, but it's a top-line unit. Or choose the lower-priced Powermax PM4 45A and save some money.
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Old 07-01-2022, 05:13 AM   #11
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Thanks everyone
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Old 07-01-2022, 10:00 AM   #12
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Set your mind at ease

Gary,
The PO of my bounder installed a PD9180 to charge a pair of T105 GCB's. The charge state of the batteries controls the amount of amps. I leave it plugged in a lot when at home, no damage to the batteries and no overcharging not even much water usage ( I add a little every few months).
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