Community Forums

CJ7365 · 02-22-2017, 10:48 AM

Wow, nice mod, and write up, for those of us that are not electrical engineers, do you think you could post up a diagram on how you wired the inverter?

Thanks for posting this

hilgert · 02-22-2017, 11:22 AM

Quote:

Originally Posted by CJ7365

Wow, nice mod, and write up, for those of us that are not electrical engineers, do you think you could post up a diagram on how you wired the inverter?

Thanks for posting this

The below is just what I did...and nothing more than free information. If you are not 100% sure of what you are doing then you should find someone that knows how to wire this stuff.

The 12VDC from the coach needs to be wired either directly from the battery to the inverter (and add a ground from the chassis of the inverter to any ground on the coach), or from some other *high current* source. I ran all three (ground, 12V+ and 12V-) to the converter panel with had high-current convenience connections for 12V.

The 12V wire needs to be big...to carry the large 12V current which is 10x the 120V current (120÷12=10x). Put another way, 120 watts at 120V is 1 amp, but 120 watts at 12V is 10 amps. I went to O'Reilly Auto and got battery cables which already had lugs on the ends for easy attachment to the inverter 12V inputs. I cut the other ends to tie into the panel (or I could have left the battery lugs on and tied to the battery).

For the 120V side I cut a utility extension cord (14 gauge wire) such that I had a 3 foot end with a plug and a 3 foot end with a receptacle...and wired them into the hardwire connections on the inverter. Then I plugged the male plug into the existing fridge outlet, which is my 120V shore power. The other end is what I plugged the fridge into...which is my inverted power or shore power, depending on whether I'm shore power or not.

The larger issue you will likely have is where to put the inverter. This was one of the reasons I used 2x4s instead of a plywood platform...easy to mount the inverter, and plenty of air space.

CJ7365 · 02-22-2017, 12:03 PM

Quote:

Originally Posted by hilgert

The below is just what I did...and nothing more than free information. If you are not 100% sure of what you are doing then you should find someone that knows how to wire this stuff.

The 12VDC from the coach needs to be wired either directly from the battery to the inverter (and add a ground from the chassis of the inverter to any ground on the coach), or from some other *high current* source. I ran all three (ground, 12V+ and 12V-) to the converter panel with had high-current convenience connections for 12V.

The 12V wire needs to be big...to carry the large 12V current which is 10x the 120V current (120÷12=10x). Put another way, 120 watts at 120V is 1 amp, but 120 watts at 12V is 10 amps. I went to O'Reilly Auto and got battery cables which already had lugs on the ends for easy attachment to the inverter 12V inputs. I cut the other ends to tie into the panel (or I could have left the battery lugs on and tied to the battery).

For the 120V side I cut a utility extension cord (14 gauge wire) such that I had a 3 foot end with a plug and a 3 foot end with a receptacle...and wired them into the hardwire connections on the inverter. Then I plugged the male plug into the existing fridge outlet, which is my 120V shore power. The other end is what I plugged the fridge into...which is my inverted power or shore power, depending on whether I'm shore power or not.

The larger issue you will likely have is where to put the inverter. This was one of the reasons I used 2x4s instead of a plywood platform...easy to mount the inverter, and plenty of air space.

Ok, well explained, thank you

twinboat · 02-22-2017, 01:55 PM

When running the battery cables to an inverter, it is recommended to keep them as short as possible. It is also advisable to run directly to the battery, to elemenate any voltage drop of other connections. The inverter manual will make recomendations. Longer 120 volt wires are always better.

A 1200 watt inverter can draw 100 amps DC, so longer, or to thin cables, can give you a low voltage shutdown, even if the batteries are OK. You should also fuse the + cable, close to the battery, to protect from short circuit fires.

As a stand alone supply for just the fridge, it should be a fine instulation, but why not tap some of that power for a TV and cell phone chargers. It can certainly handle it.

hilgert · 02-22-2017, 02:08 PM

Quote:

Originally Posted by twinboat

As a stand alone supply for just the fridge, it should be a fine instulation, but why not tap some of that power for a TV and cell phone chargers. It can certainly handle it.

My TVs are both 12v, so don't need an inverter for that. Same with phone chargers...plenty of 12v sources around MH already.

Gray01 · 02-27-2017, 01:16 PM

Hilgert,

Sir,

You mention "an electronic switch would need to be “restarted” whenever 12V power is lost."

What do you mean by "restarted"?

Can you explain that issue? when does one lose 12v power?

I am trying to understand how that would happen, and the ramifications of it.

hilgert · 02-27-2017, 02:08 PM

Quote:

Originally Posted by Gray01

Hilgert,

Sir,

You mention "an electronic switch would need to be “restarted” whenever 12V power is lost."

What do you mean by "restarted"?

Can you explain that issue? when does one lose 12v power?

I am trying to understand how that would happen, and the ramifications of it.

Some inverters don't turn "on" when you supply 12v to them...you have to press a momentary button to turn the unit on. What this means is that if you ever lose 12v for some reason (battery disconnect, whatever) the unit would not come back on automatically.

The particular inverter I used has a rocker switch (always on or always off), so after a 12v power loss it would come back on (if th switch was set to the in position).

The other reason I purchased this inverter is because it has an automatic transfer function.

driveit55 · 02-27-2017, 02:19 PM

Thanks for the info,looking to add a frig to our unit,how many batterys are for the frig and what size batt,how long will the frig run on your setup,how many amps on your frig.I though if we did a frig upgrade if were on battery power what do you think of putting a cut off switch on the defrost timer so the defrost heater are off till back on shore power,on gen on,Thanks Charles 2000 cc magna

Gray01 · 02-27-2017, 02:37 PM

Thank you sir.

twinboat · 02-27-2017, 02:37 PM

Here is My experence with switching off the defrost timer.

After 2 or 3 days, we think the frost built up and blocked the cold air flow between the fridge and freezer.

The DW said things were warning up in it, so I had to turn it back on. The next cycle, it started working fine again.

Overall it didn't seem to make that much difference in energy use. It was a 7.5 c.f. fridge and it used 9 amps, DC, when running. It ran about 1/3 the time, so that works out to 3 to 4 AHs.

hilgert · 02-27-2017, 02:50 PM

Quote:

Originally Posted by driveit55

Thanks for the info,looking to add a frig to our unit,how many batterys are for the frig and what size batt,how long will the frig run on your setup,how many amps on your frig.I though if we did a frig upgrade if were on battery power what do you think of putting a cut off switch on the defrost timer so the defrost heater are off till back on shore power,on gen on,Thanks Charles 2000 cc magna

At least with my Whirlpool it does not seem to draw much power, and as a previous poster said you really want to keep defrost working. I did not add batteries...just using the two existing house batteries.

hilgert · 03-20-2017, 11:34 AM

Update:

Still going strong...temps are -5°F in the freezer and +34°F in the fridge. Checked amp draw the other day...less than 1A when running (probably more when compressor is starting). I could not catch defrost cycle, but I'd guess it's minimal as well.

Adam1219 · 05-24-2017, 11:04 PM

I would love to change mine out too. Huge undertaking. Great write up and documentation.

Sbrownstein · 05-26-2017, 06:26 AM

Quote:

Originally Posted by hilgert

Update:

Still going strong...temps are -5°F in the freezer and +34°F in the fridge. Checked amp draw the other day...less than 1A when running (probably more when compressor is starting). I could not catch defrost cycle, but I'd guess it's minimal as well.

I measured a lot of things when my 23 cu ft Frigidaire was running and it consumes a little more than 100 watts on average...but that is pretty much 100% of the time as it uses an inverter powered compressor and is a really, really big unit! After all that work, it turns out that if you start with the Energy Star rating and work backwards and throw in an inverter efficiency number of say 80% you can almost directly come up with a pretty good number. They are real careful when doing their Energy Start testing so you might find that real life is a little less efficient. Your Whirlpool has a rating of 338 KWH per year so take 365 days and 24 hours and you get an average of 38 watts. Bump it up for the inverter at say 80% and you get around 50 watts on the inverter input. At an average of 12.25 volts you will see about 4 amps on the DC side. Means that you will consume about 90 AH in 24 hours. Not too bad.

My big unit uses about 110 AH in a 24 hour period.