Electrical anomaly~ O.T.

This has had me scratching my head for months.

Up at my shop I have some solar panels mounted on the roof. I have some large, high current capacity batteries being charged thru a charge controller. Nothing fancy. I have a pair of good panels (don't know name brand) I also have a set of the 3 panels harbor freight sells (kinda weak outut)

I have the batteries setting on a thin rubber sheet on a concrete floor out of the way. They are spill proof batteries in steel cases. Actually, what I have are twelve 2 volt cells. I make two sets of 6 and wire them in series to make 12 volts. I am charging the two 12 volt sets from the solar panels and charge controller.

That part works fine. As much sunshine as we've had recently, I could lite up Frankenstein!

Here is where the anomaly begins. I have a nice 12 volt DC/AC modified sine wave 5000 watt inverter. Didn't know about the sine/modified sine thing when I was shopping.

I have the battery banks wired parallel feeding the inverter. Works great. The digital readout on the front of it shows 12.50 volts as the thing is powering some big fans in the shop today. Probably 2 amps draw on the fans. I even run a TV and another electrical powered tool.

The fans are old. Mounted on steel pedestals. Both fans have ran for a couple of years since I got them with no indications of trouble. I usually run them off of regular 115vac right out of the wall.

My shop floor is concrete. I have quite a few sheets of 14 gage hot roll steel laying singly around on the floor- cause that's the easiest way to store them at the time. Foot traffic keeps them more or less rust free.

So, lets get to it. The other day I finally got serious and hooked all this panel/battery/inverter stuff up and was going to use it. Things all in order and I plug one of the fans in. It fires right up. It is setting on the steel sheet on the floor. Later on it is in the way, so I kinda skid it off the steel sheet and onto the DRY concrete floor..... instantly I hear the motor slow down as I drag the base across the concrete. I let it stand up vertically and the motor speeds up to normal.

I thought I had a loose wire inside the fan motor housing and investigated. Nothing. Fan is running right along when I need to move it again. As soon as I started shuffling the base around on the floor, the fan stuttered and slowed down and all of a sudden the inverter has an alarm and starts beeping and shut off it's output. I am just sure I have a bad wire, so I redo the investigation. Nothing.

Reset the alarm on the inverter and it comes right back to life. Plug the fan back in and turn it on. Runs fine. Now, I am gonna try some tests. I put the fan back up on the steel sheet and wrestle it around to try and make it do the thing it was doing, but nothing.

I leave it there on the steel. I grab the other big floor fan and plug it in.... setting on steel. Fires right up and runs fast and smooth. Drag it off the steel floor onto the concrete- instantly it shudders and slows down and the inverter alarms and shuts off.... the voltage readout on the inverter stays right where it was at.... not like it was shorting out and putting a big load on the thing.

Never any sparks from anything where it touches the floor. Nothing to indicate something was shorting to ground or whatever.

So, next test I start both fans on the steel and let them run.... grab a big pair of jumper cables and ground them to each other..... nothing.... not a wobble or shudder. Take a little volt meter and touch each housing....nothing on AC. Didn't try DC.

Next, I take one out on the concrete and let it run without moving it around to make connection with the floor as previously. Wiggle the other one on the steel....nothing. Drag it out to the concrete and instantly both of them shudder and slow down and inverter alarms out.

I have big thick sheets of steel welded together for a driveway. Laying on a fine gravel base. I take one fan out there and set it down and start it. It runs good. I wiggle the fan around on it's base and it starts shuddering and the inverter times out. Reset the alarm and set the fan down nice and easy trying not to make a good electrical contact. It's running good.

I take the little analog volt meter and touch the steel driveway and touch the fan base... it instantly acts like some reversed the voltage and it stops immediately!!!! No sparks at the point of contact of the test leads. No movement of the analog gauge! Nothing! As soon as I let off it starts back up and runs.

I walk in the shop door, grab that other fan off the steel sheet on the floor, scoot it over to the concrete floor and as soon as it touches..... zzzztttt~ they both shudder and stall and the inverter alarms out.

Damndest thing I ever seen. I wish I had a movie camera so I could document this stuff.

To recap, dry concrete floor... the inverter is insulated from the floor, but it isn't grounded to anything.... setting on rubber, too. The fans can set next to each other on steel floor inside the shop and no issues. Set together on the steel driveway outside..... stall out. Lift one up and they both start running. I have even grounded one fan to the inverter case to see if anything happens- nothing.

I got both these fans as basket cases as far as the wiring goes. They run together just fine plugged into 113vac setting on the concrete floor or the steel floor. Things only go to hell when running off inverter power. I thought maybe I had the neutral and "line" switched and that could be the problem, but dont' really thing that is it. I never get shocked touching them now or before....

I am stumped. Hope to hear some good guesses.

Sounds like a bad connection (even bad power cord) somewhere. I'm sure the steel/concrete doesn't have anything to do with it.

It's my understanding that modified sine wave inverters, as well as some other components in solar battery charging circuits, are by nature electrically "noisy", and can generate significant EMI. I'm wondering if somehow EMI is upsetting a fault circuit in the inverter? Before I get further in over my head, hopefully some PM member with true expertise in this area will provide guidance as to how to diagnose if such condition(s) exist.

BTW, are the power cords to the fans grounded types, and are you feeding power to the fans via extension cords plugged directly into the inverter?

Good luck,

~TW~

These are two prong plugs. Nothing wrong with the cords. Fan cords are plugged directly into inverter.

The fans work just fine plugged into the wall. It doesn't do anything if I set the inverter down on the concrete with the fans running, or ground the inverter to the fans!

What I thought of doing was getting into the fan and switching where I have the neutral and the line connected on one of them....or maybe both.... see if that does anything. But, still, they work just fine plugged into shore power!

Like I said, what really got me was when I had one setting on the steel sheet outdoors (inverter setting inside on rubber) and it was running until I touched the lead from the VOM meter to it and the steel at the same time and it acted like it locked up. I think it's odd that there are no electric arcs or other obvious signs of electric problems, or I don't get shocked at all when moving these things around experimenting.

I run a TV on this thing at times, and when the fans do their thing the TV goes off as the inverter shuts down. There are 4 receptacles on the front of the inverter. It is a Coleman brand. I bought if from some truck driver who used it to power things in his truck sleeper. When I am not fooling with this stuff trying to get it to mess up, I can leave the fans running for hours on end. After a bit the little cooling fan inside the inverter will come on as it warms up. Everything works just fine.

I have never seen anything like this. I think it is some sort of signal that is telling the inverter something is wrong.

Earth leakage detector / RCD getting its knickers in a twist. The electrically noisy output of a modified sine wave inverter makes the detector a bit twitchy as a matter of course. In particular if it sees a capacitor. Steel plates on floor make a (lousy) capacitor. Also the thing will be sensitive to differences in conditions on different outputs. If used in a vehicle things may not be exceptionally well tied down to ground so if all the loads float around together the thing will behave, ie both fans on steel, but if one shifts relative to the other, ie one on steel one on concrete, it will fault even though objectively things are safe.

Clive

Sounds like your system doesn't have an earth ground (neutral side connected to ground rod). That can cause problems for MSW inverters.

Now you know how Mr. Tesla felt. Must have been very confusing with no rules to go by. We have a working theory of how electricity behaves. It is just a theory. I want to know more about your steel plate driveway. Joe

Do this test: Try adding a green grounding wire from the fan to the inverter. That is to
say, convert the fan motor to have a three wire grounded plug in effect.

Ok, here are the two fans setting in place. One on the sheet steel, other on concrete. Runs fine this way.



Here is the inverter- with battery bank setting behind it. There are a pair of duplex outlets on the face of it.

I tried some more experimenting. They react differently in these scenarios plugged into different outlets- like both fans on the same duplex outlet or one fan on both~ it's too complicated to explain all the different outcomes.

Anyhow, I did ground the lug on the inverter to the short fan (cause it has nice plated steel surface compared to the painted, rusty tall fan). Nothing happened.

Grounded the lug on inverter to a rod I drove into the wet ground outside. Nothing. The fans still acted up when I touched both of them to the concrete floor at the same time.

As they set in the picture.... one on steel, one on concrete... things are hunky-dory. Slide that short fan to just barely touch the concrete floor.... they quit running.

Now, get this.... lift that short fan off the floor= touching nothing but my hands- they both die- and I am not getting the slightest tingle... as I would if I was completing a circuit with my body.

One thing I haven't done is tried to set both fans on an insulating layer to isolate them from the floor altogether. I know there is probably moisture between the steel sheet and the concrete floor making some sort of connection.

I tried so many combinations of stuff I can't type enough to explain all of them to you.

I think Clive has hit the nail on the head with his explanation. The short fan is a "Freshn'd Aire" brand of fan. It has what looks and sounds like an airplane propeller for a prop. Moves a lot of air. The other is a big Emerson. They both have capacitors in their circuits.

Right before I left to come home to type all this, I plugged them both into the wall outlet..... things run great no matter how I place the fans on the floor.

As far as my steel driveway.... it is some big 3/8ths steel sheets I got from the salvage yard. They started life as a water tower. This tower was the one that was a tall cylindrical tank on top of 4 legs with a cone shaped roof. These sheets were the sides. This salvage yard had all those sheets laying out. I thought to myself I am too tight to pour a cement drive, and that would be taxable improvement. Here is a little friend taking forklift driving lessons. She is out on the driveway, which runs from the edge of the slab in the shop out to the concrete alleyway.



So, I bought enough sheets to make a drive 12 foot wide and about 30 foot long, got out my portable welder and welded them all together. Where it bowed up a bit, I torched little holes thru the sheet and drove 1" diameter steel rebar down thru the hole til it was deep in the ground, used a forklift to set a big heavy weight on the sheet to get it down flat, welded the rod to the hole and used that method to take the bow out of the steel sheet! The weight is on that table in the picture.... laying flat there on the corner of the table. It was a weight on some sort of pile-driver pavement breaker... went up and down and on the downstroke it struck the pin that pounds into the concrete (I think). Anyway.... it's solid iron and heavy!

JoeE. said:

View attachment 82797

Ok, here are the two fans setting in place. One on the sheet steel, other on concrete. Runs fine this way.

I think Clive has hit the nail on the head with his explanation. The short fan is a "Freshn'd Aire" brand of fan. It has what looks and sounds like an airplane propeller for a prop. Moves a lot of air. The other is a big Emerson. They both have capacitors in their circuits.

.

Click to expand...

I agree. I think Clive's got something. As soon as I saw those fans I thought, "run capacitors". Could be some kind of capacitance issue in which the steel sheets are playing a (good) role. Here's a link to a website that explains the "noise" issues with modified sine wave inverters, as well as some generic fixes. The article is more slanted towards radio reception, but may give a better understanding of the problem.

Reducing Electromagnetic Interference in Solar Systems

~TW~

JoeE. said:

I am stumped. Hope to hear some good guesses.

Click to expand...

Some things are better left to a professional.

Tom

"modified sine wave" means a square wave with the pulse duration and peak voltage adjusted to produce the nominal RMS output voltage.

Motors will run fine on it, generally.

There IS, however, a goodly amount of high frequency content in the otput. For instance, many DeWalt battery chargers, and other devices, won't work right, because of that. The DeWalt chargers use a capacitor to reduce the voltage (batteries are "hot" while charging) and that won't respond right to to the square wave.

IF the inverter has some sort of leakage current sensor, it may be goofed up by your situation... 1) it isn't directly grounded, and so has no reliable reference. 2) the load grounding changes when they are on concrete vs on the steel.

If you ground your inverter (to a ground rod, the way you are supposed to per it's manual) so that it has a good ground reference, it should either work fine, or mess up in a reliably repeatable way that can be diagnosed and dealt with.

Thanks for the info. That will be easy enough to try.

I wonder if it would make any difference if the appliances in use had the 3 prong plugs and were wired accordingly?

JoeE. said:

I wonder if it would make any difference if the appliances in use had the 3 prong plugs and were wired accordingly?

Click to expand...

It might. Depends on how the leakage current sensor (if any) is set up.

"I wonder if it would make any difference if the appliances in use had the 3 prong plugs and were wired accordingly? "

Some big fat jerk in a post above suggested you try that, and the reply you gave was, you did try that and
it made no difference.

If you've not done that, I'd do that *first* thing.

+1 for it being an earthing issue, a product I used to make relied on square wave PWM switching: every single customer who complained about radio interference turned out to have a faulty earth or dangerous home wiring when examined by a licensed electrician......except for one customer who had a 1960's black and white valve TV set which had a worn out tube.

jim rozen said:

"I wonder if it would make any difference if the appliances in use had the 3 prong plugs and were wired accordingly?"

Some big fat jerk in a post above suggested you try that, and the reply you gave was, you did try that and it made no difference.

Click to expand...

Where did I write that? What I found I wrote was~ "These are two prong plugs. Nothing wrong with the cords. Fan cords are plugged directly into inverter."

Call 1-800-LENSCRAFTERS


..... or maybe I should. I don't see it.

JoeE. said:

Where did I write that? What I found I wrote was~ "These are two prong plugs. Nothing wrong with the cords. Fan cords are plugged directly into inverter."

Call 1-800-LENSCRAFTERS


..... or maybe I should. I don't see it.

Click to expand...

Metal fans with no ground prong? Add a ground wire using an alligator clip as suggested in post #8 and see if the problem continues.
Your response indicated you tried this:

Anyhow, I did ground the lug on the inverter to the short fan (cause it has nice plated steel surface compared to the painted, rusty tall fan). Nothing happened.

Click to expand...

Regardless, metal fans should be retrofitted with 3 prong plug to protect you if they eventually develop an internal short.

is the 2 wire cord polarized? if not, maybe that is your problem - all grounding should be at a common point - multiple earth grounds reek havoc on electronic circuits - sometimes the motor has a slight grounding but high enough resistance not to conduct much current but enough to destabilize the electronics.