Need help designing a solar charging system - Fiberglass RV


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Old 07-02-2015, 12:15 PM   #1
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Need help designing a solar charging system

In order to accurately determine my needs for a solar system, I need to know the current draw of the appliances I use in our 13' Scamp.

Can anyone tell me the draw of these items:
Dometic RM2193 3 way refrigerator (On 12 volt, not propane, although I don't foresee actually running it on 12v)
Suburban NT-16SEQ Furnace

Bonus!
I called Fan-Tastic Vent about our model 4000R. They supplied this data on current draw:
High 3.00 amps
Med 2.20 amps
Low 1.86 amps
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Old 07-02-2015, 12:41 PM   #2
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Dometic RM2193 = 10 amps (actually 9.8)
NT-16 furnaces = 3.8 amps (as measured on mine)
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Old 07-02-2015, 12:45 PM   #3
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You can run the device while the power is measured with a volt-ohm meter set on amps. Attach one lead to positive on device, and other lead to positive at battery source to power device. Amperage will vary as device requirements change (e.g.: low, medium, high).
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Old 07-02-2015, 01:13 PM   #4
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Just a quick note. Those Fantastic fan numbers can be deceiving. The fan motor may be drawing the nominal amps the company indicated, but regardless of speed, the fan will be drawing that 3 amps or so, the balance being burned up in resistance coils, ie, heat.

Many of us here have replaced the original speed control with a pulse width modulated speed control (about 6 bucks online) which controls the fan speed by rapidly turning the power on and off.

If a battery monitor is part of your solar installation, you can use the PWM controller to dial in the speed you need for comfort and see exactly the amps are being used. At night, in my small trailer, I am using about .5 amps.........no amps wasted on heat.
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Old 07-02-2015, 01:31 PM   #5
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Measuring amps

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You can run the device while the power is measured with a volt-ohm meter set on amps. Attach one lead to positive on device, and other lead to positive at battery source to power device. Amperage will vary as device requirements change (e.g.: low, medium, high).
But be careful.... Most hand held multimeters are fused at 10 amps for current, some even less, and you can blow the internal fuse if you exceed that value. Much better to use a AC/DC Amp Clamp/Multimeter, Such as the Sears Craftsman 400A, one of the best electrical tools in my tool box.
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Old 07-02-2015, 08:01 PM   #6
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Bob, thanks for the information. I use the free multimeters from Harbor Freight, but when the last of them gets fried I'll opt for one like yours.
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Old 07-02-2015, 09:13 PM   #7
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Amp draw is not the only issue with solar . Charge voltages are also a consideration
My Renogy solar suitcase has a boost charge voltage level of 14.6 VDC & an equalization voltage level of 14.8 to 15.0 VDC. Both of these parameters match. up with the charge level voltages recommended by the battery manufacturer .
Unfortunately the equipment in my trailer is rated for -< 13.8 VDC .
(Fan ,LED lights ,water pump ,radio, furnace Etc.) I called the tech dept of the equipment supplers / manufacturers to verify the max voltage.
I wondered why the factory converter / battery charger on my Casita was single stage with a. maximum output of 13.8 VDC . Now I know !!
The answer I received to cure this problem was to disconnect the trailer's equipment from the bsttery when charging with solar . Makes it hard to keep the beer cold with the refrigerator off.
Some of the newer 3 stage charger / converters have the same issue.
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Old 07-02-2015, 09:30 PM   #8
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[QUOTE=steve dunham;532618]Amp draw is not the only issue with solar . Charge voltages are also a consideration
My Renogy solar suitcase has a boost charge voltage level of 14.6 VDC & an equalization voltage level of 14.8 to 15.0 VDC. Both of these parameters match. up with the charge level voltages recommended by the battery manufacturer .
Unfortunately the equipment in my trailer is rated for -< 13.8 VDC .
(Fan ,LED lights ,water pump ,radio, furnace Etc.) I called the tech dept of the equipment supplers / manufacturers to verify the max voltage.[QUOTE]

I worried about this before ordering a 12V Truckfridge and contacted them concerning this. The information they provided seems to indicate their unit has a 17V limit. I don't know anything about other appliances or lights but wonder how hard the occasional over-voltage situation would be long or short term? Maybe something like an inline voltage cut-out could be used?
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Old 07-02-2015, 10:45 PM   #9
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Free....

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Bob, thanks for the information. I use the free multimeters from Harbor Freight, but when the last of them gets fried I'll opt for one like yours.
Those free HF multimeters are worth exactly what you paid for them, both in terms of accuracy and reliability. I've tried three of them and none of them agreed with each other when reading battery voltages.

As I place a value on my time and the quality of my tools, that Craftsman meter, on it's 5th year of use, has cost less than $.05 a day, and does a whole lot things that the freebies can't do. It's a cheap investment.
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Old 07-03-2015, 06:18 PM   #10
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In order to actually call it a solar power system there needs to be a charge controller between the panels and the battery. These come in a multitude of complexities depending on the intended use. Solar panels may put out voltages well in excess of 13.8. The controller protects the battery and the other components from over-voltage conditions.
Without a charge controller not only will you burn out 12v toys, you won't be doing your battery any favors either!
Get an appropriate controller and enjoy cold beer anywhere!


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Old 07-03-2015, 06:51 PM   #11
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Quote:
Originally Posted by Martin B. View Post

Can anyone tell me the draw of these items:
Dometic RM2193 3 way refrigerator (On 12 volt, not propane, although I don't foresee actually running it on 12v)
Not running in on 12V is a good thing otherwise I think you will find as many of us with solar system have that is one VERY power hunger appliance best run on propane if not plugged into power. To have enough power to run it around the clock on 12v you would need a system with 2 6v batteries, guaranteed full sun each day and enough solar panels to cover the roof of your trailer.
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Old 07-03-2015, 07:42 PM   #12
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Originally Posted by Denece View Post
In order to actually call it a solar power system there needs to be a charge controller between the panels and the battery. These come in a multitude of complexities depending on the intended use. Solar panels may put out voltages well in excess of 13.8. The controller protects the battery and the other components from over-voltage conditions.
Without a charge controller not only will you burn out 12v toys, you won't be doing your battery any favors either!
Get an appropriate controller and enjoy cold beer anywhere!


Sent from my iPhone using Fiberglass RV
My Renogy Solar system came with a charge controller . The controller has 4 levels of charging . The charge parameters are adjustable within limits . The. instruction booklet that
came with the controller gives a specific warning that the boost and equalization voltages provided by the controller may be harmful to connected equipment
and advises you to disconnect all loads when charging the battery,
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Old 07-04-2015, 01:01 AM   #13
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We lived on solar only on a sailboat for eight years. We never disconnected loads to charge. That is a totally unnecessary complication. That is what I am trying to tell you. A proper charge controller meters the voltage going into your battery. A good one even compensates for the temperature of the battery .
There are any number of good sources for information on the web or in books. This is not rocket science, but you do want to get it right.
We have two little panels, a 20 year old controller and one deep cycle group 27. We never plug in. We always have power. You can too


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Old 07-04-2015, 08:12 AM   #14
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Quote from Renogy. (Charge controller instruction manual)

" WARNING : EQUALIZATION MAY INCREASE BATTERY VOLTAGE TO A LEVEL DAMAGING TO DC LOADS .ENSURE THAT ALL LOAD ALLOWABLE IMPUT VOLTAGES ARE
GREATER THAN THE EQUALIZATION CHARGING SET POINT"

MAYBE RENOGY'S ENGINEERS ARE NOT ROCKET SCIENTIST EITHER !!
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