Wiring SAE plugs and polarity... costly learning experience

[jethro]

Maybe you've seen my battery box build using Amped Outdoors LiFePo4 batteries: https://www.iceshanty.com/ice_fishing/index.php?topic=371660.msg4010860#msg4010860

Anyway, I have learned a somewhat costly lesson that I would like to make sure no one else duplicates. I went back and forth on connectors for my devices and decided on SAE plugs. I like them, I have some devices on my snowmobile and motorcycle that use them, they are durable and all that. Now a picture... notice anything different about these two SAE connectors?



Yep, automotive devices and solar devices, both which use a lot of SAE connectors, have the reverse polarity. There is a big movement of people building solar generators for camping, off grid living, preppers.. a lot of that is sold on Amazon, which is where I got a lot of my supplies. But I am not building a solar battery box, I'm building a wiring harness to power my portable and I have a lot of devices, some of which I bought that are automotive oriented.

So I wired 4 of these plugs I bought off Amazon, which are solar oriented, into my battery box:



I then mocked up part of my wiring harness temporarily and used a different wire, one from an automotive application. When I switched wires to a solar wire, I had no idea the polarity is different. I first blew up a small, SAE to USB adapter. I thought it was dead on arrival, but only later learned I probably blew it up with incorrect polarity. After that I fried a cigarette plug splitter for USB. I then smoked a 12v adapter for my 10.1" monitor that I use with my camera. Like literally smoked, I could smell the electrical fire. That was when I realized the issue and discovered that the polarity for automotive is direct opposite than solar. Best I can surmise, the reason is that when you have an SAE plug on a motorcycle, they want the hot to be the shielded terminal so it has less of a chance of shorting against the chassis if the cover comes off. But with solar and charging a battery from a panel, the hot charge is in reverse because you are feeding the battery instead. It was very confusing for me until I figured it out.

So the moral of the story is, if you are using SAE plugs, cords, adapters and the like, make sure you are aware they do not all follow the same polarity! Maybe someone will learn from my mistake which cost me about $40!!

[SLAYERFISH]

But if you plug those two plugs together red is red and black is black.

[jethro]

But if you plug those two plugs together red is red and black is black.

I know, this is complicated and took me some time to figure out... But the problem isn't really the cords, it's the socket itself- the second picture I posted. Or more accurately the way I wired the sockets, with red being positive and black being negative (like you would expect). The cords just clued me in to why I am blowing up my devices and fuses. So the second picture, the actual panel mount plug, the un-shielded terminal leaving the battery box is hot. This is the direct opposite of how automotive power plugs work. On a motorcycle that has SAE plugs, the un-shielded terminal leaving the vehicle is ground. With solar devices they wire the plugs direct opposite because the power is flowing into the battery instead of out of it. Or at least that is the best meaning I can surmise.

So the problem isn't really the cords, or the devices, it's how you wire the box and what plugs you go with.

I am learning this as I go, and I am an electrical idiot, so I may be even more screwed up than I know.

[jethro]

But if you plug those two plugs together red is red and black is black.

It's friggin' crazy... yes, if you plug those cords together the red stays red and the black stays black, but look, the plugs are wired in direct opposite of each other. At the panel the polarity would be reversed using these cords. Look how the terminals are opposite. One of the cords is for auto application and one is for solar.

[SLAYERFISH]

Oh yeah I truly see what grief that could cause.   I'm a EE and have smoked many a wire/ device!

[esox_xtm]

They come in pairs for a reason.  Generally the connector coming from the power source has the shrouded positive lead so it can't accidentally short the battery. Once it's connected to the device it's completely covered.

In your 2nd pic the connector on the right would come from the PS and the one on left would be wired to the device. Once plugged together polarity is correct and you battery/PS is protected from shorting when unplugged.

And yes, red to red and black to black. Gotta keep 'em segregated... I bet what happened is you left the dongle in the 1st pic as it was and instead of separating the connectors (that's the intention BTW) and using the back end on your device you just plugged in another SAE plug effectively reversing the polarity. So that 1st pic is a "pair" of connectors. Cut the wire in the middle, solder, crimp, what have you the power source to the wires on the panel part and use the other, matched half to go to your device. Correct polarity. EZPZ.

[RyanW]

They come in pairs for a reason.  Generally the connector coming from the power source has the shrouded positive lead so it can't accidentally short the battery. Once it's connected to the device it's completely covered.

In your 2nd pic the connector on the right would come from the PS and the one on left would be wired to the device. Once plugged together polarity is correct and you battery/PS is protected from shorting when unplugged.

And yes, red to red and black to black. Gotta keep 'em segregated... I bet what happened is you left the dongle in the 1st pic as it was and instead of separating the connectors (that's the intention BTW) and using the back end on your device you just plugged in another SAE plug effectively reversing the polarity. So that 1st pic is a "pair" of connectors. Cut the wire in the middle, solder, crimp, what have you the power source to the wires on the panel part and use the other, matched half to go to your device. Correct polarity. EZPZ.

This. You said it much better than the mess I was typing out.

[jethro]

No Esox, that first pic is two different cords. One is designed for solar charging, one is for auto/powersports use, because like you say, the shielded plug would be opposite in both scenarios. But everything you said, yes, totally correct!! I just didn't realize there was different polarity for which way the power is flowing, but makes total sense.

[Royalwapiti]

I figured it out a number of years when I hardwired a maintainer to my KLR650 motorcycle.   I had to burn marks with the correct polarity into the cord end so i knew which was going to the hot, some chargers were different.

Got lucky those lithium bats can burn hot!

[jethro]

I figured it out a number of years when I hardwired a maintainer to my KLR650 motorcycle.   I had to burn marks with the correct polarity into the cord end so i knew which was going to the hot, some chargers were different.

Got lucky those lithium bats can burn hot!

 

[esox_xtm]

No Esox, that first pic is two different cords.

Got that doc but the premise is still the same. Cables/cord with like connectors are not designed with polarity reversed for different applications. However one connector is designed for output and the mate is designed for input. But I see the problem now. The reason the unshielded connector is leaving the box hot is because (I'd bet) wired a connector correctly from the battery array and plugged it into the (what you thought was) the "rear connector" of the panel mount effectively reversing the polarity at that point. Again, the intention of that panel mount "pair" or just a regular pair is to cut them apart, connect correctly to battery/PS and device(s) and go. They are NOT interchangeable! Output - input, remember? Generally speaking the output side of the circuit will always have the positive side of the connector shielded.

Now you did raise another point that I had not considered regarding using a solar source to charge or in conjunction with this setup. I just verified on my Coleman panel that the SAE plug has the + side shielded. The mistake here would be to try to connect this directly to a correctly wired SAE plug on the battery array. Now we've got + to - and - to +. No good, sparks gonna fly. As to how to correctly wire this part I'd have to think on that a bit. Simplest deal would be a gender bender jumper where polarity is intentionally reversed so you would connect the + of the panel to the + of the battery. I've got some panel documentation around somewhere. Gonna see if I can find it and see what it has to say about battery maintenance.

OK, found it. So first, on panels of 15W or more a charging controller is strongly recommended. Happened to get one of those with my panel. The controller can be wired directly to the panel OR (if the panel is equipped with a "quick connect" plug) a "reversing" plug/connector is included with the hardware. Instructions have the positive lead unshielded going TO the controller. Interestingly THAT LEAD IS RED. The one FROM the battery is shielded AND THAT LEAD IS ALSO RED. Leads coming from the controller end in terminal rings, are red and black, + and - respectively. Also included are a pair of battery clips with a QC/SAE connector that is proper for the device side of an SAE connector pair.

So, doc, I'm sorry for your loss and trouble but have to thank you for sharing. I do have intentions of using this solar panel and almost certainly would have bumped into the polarity conundrum. Thanks for blazing the trail!

[jethro]

The reason the unshielded connector is leaving the box hot is because (I'd bet) wired a connector correctly from the battery array and plugged it into the (what you thought was) the "rear connector" of the panel mount effectively reversing the polarity at that point.

Basically, yes. The way I found all this out is even more screwed up. You got the idea though for the most part. I did as you said use the panel mounts and cut them as a matched pair for my devices (lights, fish finder). The problem happened when I used a different cable and set up with a cigarette lighter plug (that is designed for the Battery Tender brand of devices where the unshielded plug is supposed to be the ground or black wire) and then decided to change the plug to an SAE which changed the polarity of my wiring. My 10.1" monitor uses a 12v cigarette style plug.

This picture will actually explain everything! Look at the plug and see that when I plug it into my "solar charging" panel mount plugs that the red becomes black and the black becomes red. That's the difference between Auto/Powersports plugs and solar charging plugs if I am understanding this correctly!



I'm still confused but at least I know why!

[esox_xtm]

Just remember it this way. Always gotta know which is plus and which is minus I can see that interfacing another powered system can present issues if you assume the + will always be shielded and always have a red lead. On my solar panel they provided a correctly wire plug red for + but unshielded from panel to controller, wired backwards if you will. On home brew deals we dont have access to "backwards" wired plugs so it's easy to get it screwed up.

One way to keep everything straight is to design the circuit(s) so all the polarities are correct with correctly colored wires and all current outputs only have output connectors (+ side shielded). Then make yourself a gender bender where it appears the jumper intentionally reverses polarity but will actually connect an output (from a solar panel or other charger) to your batteries. That way there's no way to accidentally connect anything incorrectly and the jumper only gets used for charging purposes.

Again, it's not "auto/powersports" plugs vs "solar/charging" plugs. It's only output plugs and input plugs. In charging/maintenance situations, if any polarized connection is used, one of the sides will be "out of code" to make the correct polarity interface. No different designs for different purposes, just exception(s) to the rule for certain circumstances.

[youngster]

im not the brightest bulb when it comes to electronis.. am I safe to say as long as plus go to plus and minus to minus wether coming or going... im safe/    another don't use the assumption the the shielded saide or unshielded could be either a plus or minus. as long as plus is hooked to plus and negative to negative ,, it could be any kind of socket or colored wire...   just tryin to see it as simple and uncluttered as I can. thanks in advance.

[latremorej]

They come in pairs for a reason.  Generally the connector coming from the power source has the shrouded positive lead so it can't accidentally short the battery. Once it's connected to the device it's completely covered.

Yup

I knew this going in as well.... however, on one of my elekchicken escapades, I still managed to cross it... burned out a camera once!

Jason

[ndfisher]

I imagine 40 years ago this wasn't much of a problem    I'm just as guilty as anyone for having gadgets and "necessary" electronics with me too.  I think everyone should have a multi-meter for checking polarity, continuity, voltage, ect.  I know Harbor Freight doesn't always have the highest quality stuff but for less than 10 bucks it will sure get the job done most of the time...and you can spend more on the "necessary" items!!

[youngster]

ive done the same watch smoke fire up and say to myself ,huh....  lots of R&D,   lol

[esox_xtm]

I think everyone should have a multi-meter for checking polarity, continuity, voltage, ect. 

Having one and knowing how to use it are two very different things. The old man had one in with his big box of electrical "stuff". I saw him remove it from the package, spin the selector knob a couple times, flip the switches then return it to the package never to be touched by him again.
 
On the other hand I own three. Still prefer the 35 year old Radio Shack analog to the two digital models; one a pretty decent Sperry instruments and the other a HF special.

[slipperybob]

Yes, that's right...all right.