Using External SAE Solar Port as Power Supply

manyman297 · May 2023

I recall a while back somebody mentioning that you can reverse the polarity on the external solar port to provide 12v power.

I'm guessing you could simply reverse the connections on the SAE plug running to your appliance (a portable 12v fridge in my case) and add an inline fuse? Does that sound correct?

ScottG · May 2023

Assuming the port is wired directly to the battery, there's no reason electrically why this would not work. I agree adding a fuse (on the positive leg) is a good idea.

I do get a little skidgy when people talk about "reversing the polarity" as I think the phrase is misleading. Positive always needs to be connected to positive, and negative to negative, and you need to be darn sure you've got that correct. To do so, you may need to swap leads or use an adapter to change which pin carries which leg, but in doing so you are technically maintaining the polarity, not reversing it. Rant over! :-)

Grumpy_G · May 2023

Basically yes, just check the polarity of both the fridge and the connector at the trailer. The SAE connectors are ambiguous so you may or may not need to reverse the polarity.

RTWCTS · May 2023

Polarity isn't the issue here. You are simply talking about direction of current flow, charging vs. discharging the battery. Positive is still positive and negative is still negative. And yes, fuse the line you connect to the SAE port to protect the fridge.

Edit to add: My comment assumes the SAE port connects directly to the battery terminals. If there is an on-board solar controller between the battery and the port, it won't work. You'd need a different path to the fridge.

pthomas745 · May 2023

There is a thread in this group (somewhere) that discusses the use of the SAE port as a power source. I made my own little cable with an SAE plug on one end for the port, and a 12V plug on the other, and use a small inverter in it, or even a small USB port.

There is nothing "wrong" with the polarity of the SAE port. It works exactly the way it is supposed to work. Here is an example. (I do have a better one of these with a fuse.) The key to the SAE cable: the positive side of the wiring from the battery is the "top" part of the port on the trailer in 99 percent of the cases. You want the cable you are plugging in to the port to be wired so the positive wire is "inside" the plastic part of the cable. The big metal part of the cable is the negative side of the cable.

In this picture, it is simply powering a small battery monitor. I've used a small USB adapter to power things like a high def TV antenna. I've plugged in a small inverter and used smaller items. My 2017 solar port wiring is not fused, but I know newer trailers have fuses for the wiring to the battery. I don't know what those fuses are rated for, but the 12V ports inside the trailer are on a 15 amp fuse, which limits the use of the 12V ports to items of 180 watts.

I have an Alpicool 12V fridge that is rated at 45 watts. I'm sure this little dongle would run it through the SAE port. If the weather holds out today, I'll try it out.

Image: https://us.v-cdn.net/5021717/uploads/editor/5g/85dnsjoblb5j.jpg

This is all you need to do to prove to yourself how the SAE port is wired. The "positive" side of whatever I plug into the port must be "inside the plastic" of the cable, not wired to the metal part.

db_cooper · May 2023

I use the solar port on our 2015 to power a portable fridge we keep in the TV, as well as to connect a battery tender in storage. I also have a Zamp solar suitcase that uses the port as originally wired. My solution was to change the port wires to work with the battery tender and fridge, since I use them much more than the solar panel.

I use an adapter with the Zamp panel, knowing that I have to be careful not to ground myself accidentally and getting shocked by the panel, which is the reason the port is wired differently to begin with. I prefer to do it this way to avoid accidentally connecting the fridge or battery tender without the adapter.

https://www.amazon.com/Connector-Switching-Disconnect-Automotive-Maintainer/dp/B09B77C4YX/ref=sr_1_3?crid=3W21SHR7SY8E3&keywords=sae+polarity+reverse+adapter&qid=1683133796&sprefix=sae+%2Caps%2C202&sr=8-3

pthomas745 · May 2023

Here is my SAE/12V cable with a small voltmeter plugged in. Properly wired, there is no need for an adapter. Since the SAE port is wired directly to the battery, this would be a very easy way to take voltage readings from the battery with these small voltage devices. The battery switch can be off, and the battery "rested" reading taken. As simple as can be. (The sun didn't cooperate! The LED readout is not picked up well by the cell phone camera!)

And: I could not find my version with the built in fuse holder. Since I knew the fridge only draws 45 watts, I felt comfortable using this cable for the test.

Here is my Alpicool fridge running on the same adapter.

There are plenty of these types of 12V cables available. The SAE cables were used extensively by motorcycle riders to power 12V hand warmers and things like that. The cable linked below seems to be properly wired: note the "red" positive cable terminating "inside the plastic" of the plug. My multimeter has been my best friend while decoding the SAE port. I don't automatically trust any of these devices until I check the continuity.

https://www.amazon.com/QOFOWIN-Motorcycle-Cigarette-Connection-Accessories/dp/B0BCPXQP4P/ref=sr_1_11?crid=2ZD39KBSIC23N&keywords=12v+female+port+to+sae+cable&qid=1683138556&s=automotive&sprefix=12v+female+port+to+sae+cable,automotive,132&sr=1-11&th=1

AnOldUR · May 2023

As mentioned previously, in some cases the solar controller is located in the tub to reduce voltage drop from the solar panel. This is how mine is wired so it's not possible to use the SAE port as a power source . What I did and something to consider is adding a fused cigarette lighter socket to your tub. Most 12V fridges have a cigarette lighter plug making it an easier connection.

Image: https://us.v-cdn.net/5021717/uploads/editor/4j/lo7hkrgh24wc.jpg

Our extra 12V fridge has a high minimum voltage cutoff (prevents drawing the battery down too far). Voltage drop to other cigarette lighter ports caused the fridge to shut off before it was necessary. I wired this port with a short run directly to the battery and it solved the problem.

manyman297 · May 2023

ScottG said:

Assuming the port is wired directly to the battery, there's no reason electrically why this would not work. I agree adding a fuse (on the positive leg) is a good idea.
I do get a little skidgy when people talk about "reversing the polarity" as I think the phrase is misleading. Positive always needs to be connected to positive, and negative to negative, and you need to be darn sure you've got that correct. To do so, you may need to swap leads or use an adapter to change which pin carries which leg, but in doing so you are technically maintaining the polarity, not reversing it. Rant over! :-)

You’re totally right. I’m not reversing the polarity. Didn’t even occur to me that I’m just rerouting the negative positive to opposing sides.

manyman297 · May 2023

pthomas745 said:

There is a thread in this group (somewhere) that discusses the use of the SAE port as a power source. I made my own little cable with an SAE plug on one end for the port, and a 12V plug on the other, and use a small inverter in it, or even a small USB port.
There is nothing "wrong" with the polarity of the SAE port. It works exactly the way it is supposed to work. Here is an example. (I do have a better one of these with a fuse.) The key to the SAE cable: the positive side of the wiring from the battery is the "top" part of the port on the trailer in 99 percent of the cases. You want the cable you are plugging in to the port to be wired so the positive wire is "inside" the plastic part of the cable. The big metal part of the cable is the negative side of the cable.
In this picture, it is simply powering a small battery monitor. I've used a small USB adapter to power things like a high def TV antenna. I've plugged in a small inverter and used smaller items. My 2017 solar port wiring is not fused, but I know newer trailers have fuses for the wiring to the battery. I don't know what those fuses are rated for, but the 12V ports inside the trailer are on a 15 amp fuse, which limits the use of the 12V ports to items of 180 watts.
I have an Alpicool 12V fridge that is rated at 45 watts. I'm sure this little dongle would run it through the SAE port. If the weather holds out today, I'll try it out.

This is all you need to do to prove to yourself how the SAE port is wired. The "positive" side of whatever I plug into the port must be "inside the plastic" of the cable, not wired to the metal part.

Great info!

Voltage drop is something I didn’t consider. I’ll be running that cable back to my truck’s bed where the fridge will be. Need to find some charts online to figure out gauge/voltage drop.

rcarlson1957 · May 2023

I have both an SAE port and a 12v port (both with covers) on the side of the front tub. The SAE port is wired to my solar controller in the tub and use it to connect portable a solar panel to charge camper battery when boondocking. The 12v port is wired to a small fuse panel for anything I may need to power 12v with. Don't use the 2nd one much. Originally put it in for my ICECO GO 20 frig/freezer but if have shore power I plug it into the outside A/C outlet and if boondocking I run it off a solar battery bank with controller connected to a another portable solar panel.

SLJ · May 2023

I have a solar converter in the front tub so using the SAE port on the outside is a no go. It would be more convenient for me to have an external port on the door side under the awning anyway so I will eventually mount a fused SAE port next to the outside USB port I've already installed and use the same switched 12 volt feed I ran for that.

Image: https://us.v-cdn.net/5021717/uploads/editor/b0/yca15ct34tu7.jpg

pthomas745 · May 2023

@manyman297 The Alpicool fridge I use is the "21 quart" version, and it draws only 45 watts. I just went out and looked at the 12V cable it uses, and it is 16AWG and about 7 feet long.

manyman297 · May 2023

SLJ said:

I have a solar converter in the front tub so using the SAE port on the outside is a no go. It would be more convenient for me to have an external port on the door side under the awning anyway so I will eventually mount a fused SAE port next to the outside USB port I've already installed and use the same switched 12 volt feed I ran for that.

Definitely makes more sense on this side of the camper. Down the road I'd eventually install a 12v port here, run a cord to my truck and have the fridge in the bed.

manyman297 · May 2023

pthomas745 said:

@manyman297 The Alpicool fridge I use is the "21 quart" version, and it draws only 45 watts. I just went out and looked at the 12V cable it uses, and it is 16AWG and about 7 feet long.

I need to see what the gauge is from the SAE port to the battery. My guess is it's at least 16AWG if not thicker.

AnOldUR · May 2023

Although not exactly on topic, another advantage of having either an uncontrolled SAE port or cigarette lighter socket tied to the battery is that you can connect a smart charger to it. I switched to lithium batteries, but did not update my WFCO converter. I can put a cigarette lighter adapter on my NOCO Genius10 and top off the batteries with either shore or generator power when solar isn't keeping up.

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