Noise on a 12V DC circuit.

[tanner0441]

Hi

I found that a 12V LED strip light with touch on/off wouldn't light when I wired it over my solar controll board. Removed it took it into the house and tried it on a seperate battery, perfect on off repeatedly every time I poked the touch pad.

So armed with a portable scope i went hunting. Didn't have to look far, right at the battery terminals superimposed on the 12V the was 5V AC spikes. 5V peak to peak and ringing for 10 micro seconds. switched the panels off still there. I have two controllers a MPPT with 750 W of solar and a PWM with 60W which will eventually moved to another building.

At this point I ran out ot time so had to shelve the hunt. But I think my easiest option is to build a little 5A common mode filter I have plenty of toroids that are suitable. Just a bit annoying that three 12V batteries in parallel (with buss bars) are not low enough impedance to keep the cr#p from a charge controller out of the connected circuits. I spent a lot of my working life keeping RF and pulse signals off DC PCB tracks.

Anyone else encountered this?

Brian

[joestue]

I doubt this is a common mode problem.

[tanner0441]

Hi

I haven't had time to get right into it. I know what the transients look like I know the duration of them but not the frequency they occure. They are not from the MPPT controller that produces hash on the output leads around 100 khz and very low level, so I am assuming the big spikes are from the PWM controller.  This is a pulse with ringing. the best way I can describe it is like the primary patern on a car ignition system when the points open.

I thought common mode filtering because it is a symetrical patern and they are easy to make and I can put one in the lead from the controller and the battery. I used to build  LISN filters for cleaning mains supplies for measuring complience in RF circuits and preventing the RF getting back up the mains leads, but it is easy when you know what frequencies you are dealing with.

As a PS cordless oscilloscopes are like cordless power tools the batteries go flat right in the middle of a job.

Brian

[Mary B]

A simple .01mfd ceramic disc capacitor across +- might cure the problem. And is cheap. May be a sign your charge controller has something failing...

[OperaHouse]

That is why I save the inductors out of old computer power supplies, designed with a nice lossy core. I just got one of these and I love it. Less than $29 shipped with taxes and that is with the deluxe test lead package. Love I can take it anywhere.

[tanner0441]

Hi

I have one of those coming I also have a 4 channel 60Mhz version that can hook up to a PC for data logging,  I was using it the weekend to find the transients in the first place I have a nice selection of toroids and prewound toroids out of PSU filters and pages of data sheets on powdered iron, wound iron and ferrite. The problem if focusing for long enough to sort it without going off at a tangent. Bit like sorting piles of magazines you always come across articles you don't remember reading.

I could have a couple of days later in the week where she who would like to be obayed is going to her daughters dog sitting and i will be able to eat when I feel like it and concentrate better.

Brian

Oh I've tried a range of capacitors across various points in the circuits to no avail hence the need for propper filtering..

[OperaHouse]

For anybody else wanting one of these.  Find a vendor that baits you with a low price which is actually the extra probe kit and get them to ship that with the scope.  Eventually I'll lose that BNC adaptor and have to pay thru the nose to get another one.  Also thought it would be easy to get pre made cables with that little MDX or whatever connector that is.  Haven't found them yet.

[JW]

One thing I have done is go to a local electronics store. the one I'm referring to is in Miami Fl and I  buy my mosfets there. I'm in another state now but when we get on a project, we  check prices there first.

[Mary B]

For anybody else wanting one of these.  Find a vendor that baits you with a low price which is actually the extra probe kit and get them to ship that with the scope.  Eventually I'll lose that BNC adaptor and have to pay thru the nose to get another one.  Also thought it would be easy to get pre made cables with that little MDX or whatever connector that is.  Haven't found them yet.

post a pic of the connector... I do a LOT of RF stuff and probably have a source for the adapter

[Bruce S]

For anybody else wanting one of these.  Find a vendor that baits you with a low price which is actually the extra probe kit and get them to ship that with the scope.  Eventually I'll lose that BNC adaptor and have to pay thru the nose to get another one.  Also thought it would be easy to get pre made cables with that little MDX or whatever connector that is.  Haven't found them yet.

post a pic of the connector... I do a LOT of RF stuff and probably have a source for the adapter

Same here, we have different Radio stuff, old and new that may be easy for us to hunt down or pull out from a wall bin.

Bruce S

[tanner0441]

Hi

My other little 60Mhz scope came with two premade leads with the correct plug on rated to 100 Mhz. so if needed they will be used. I bought a cheap probe with the correct plug on, when I say cheap it fell into the cheap sh## class  but the lead was good spec so I cut the probe off the end and fitted a flying BNC on the end and I used that with the AC current probe from the HP scope I have in the loft with a dead timebase so no display.

What I've decided to do is split the system back to 24V with 760W of solar and 12V with 200W of solar that for one will isolate the problem to one or the other reducing the variables.

Also when I go to 24V I can go to 1440W of solar and I can buy 370W 36V panels for £115 GBP as long as I collect them.

Brian..

[tanner0441]

Hi

I kave myself a suitable kick up the #### and located the problem, located not cured.  The constant noise is from the MPPT controller and runs from 66Khz to 78Khz the pulses are from the PWM controller. The two together give a very strange waveform on a scope because it doesnt know which one to lock on. But several runs on single shot I was able to see them and with a ten turn 4in loop I was abble to identify the source. 

Tomorrow Im going to clip current transformers round the cables and see if I can isolate things further.

I overcame the LED lighting problem by mounting the light fitting on a strip of wood to isolate it from the aluminised plastic and foam insulation sheeting lining the roof.


Brian