How I Connected An External Fan To My Grid Tie Inverter

Started by electron, Mar 29, 2024, 12:16 AM

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If you are going to run a Power Jack type Grid Tie Inverter at full output, it's a good idea to move some extra air over the case.

A lot of people have put small 80 mm PC power supply type fans outside of the GTI and it seems to work good.

The problem is, how do you make them turn on and off only when needed like the little one inside does?

A quick calculation showed me that running the fan 10 hours a day at about 2W would be 20 Wh a day wasted (sort of). Plus wearing out the fan quicker.

I did some measurements and decided to use a 80 mm PC style fan instead of the one supplied and also to run the GTI with the cover off and blow air directly at the circuit board and transformer.

I can run it with the cover off because I am the only one with access here and it's in a place where it's hard to put your hand in there. It's also sitting flat on top of a big piece of metal and away from anything that could catch fire.

FIRE RISK IS SOMETHING YOU NEED TO THINK ABOUT - If this thing decides to go poof, normally it should be mostly contained inside the metal case, but when you remove the cover like I did then you are taking a risk of fire.

You have been warned. I am just showing you what I did.

I may change this set up later and put things back to normal and run an external fan blowing on the outside of the GTI.

The internal fan runs off of the 10V inside the GTI, that comes from a LM317 regulation circuit. The LM317 has it's own heat sink. See below for technical details.

This GTI is the OLDER style, with the flat top.

The pics below show you the adapter cable I made for this from an old dead portable phone battery. Example batteries are shown too. You could simply cut the fan wires and splice them to the connector cable then tape them up. I added the extra pins because I am always changing things and had a hard drive power connector adapter running a different fan.

I took pics of some old PC power supply cases, you can see how you end up with enough extra metal to cut and make a nice fan holder. The metal is easily bent to shape to what you want. You already need to screw down the GTI so you can use those mounting screws to hold your fan in place.

Technical Details:

The internal fan runs off of the 10V inside the GTI, this comes from a LM317 regulation circuit. The LM317 has a heat sink on it and is rated for only 1.5A max.

The LM317 is powering other things and gets pretty hot already so you don't want to load it much more.


When I measured the fans directly, the small internal fan draws about 80 mA and the new bigger 80 mm fan draws 120 mA. The LM317 inside the GTI seems to be OK with that little extra 40 mA amount but I wouldn't push it too much more.

You can make your own external LM317 circuit and make it adjustable so the fan isn't too loud. The only problem is that it won't go on and off only when the GTI needs it. I may make a post later about a way to do that.

Here's a simple LM317 circuit and calculator for figuring out resistor values. It only needs 2 resistors for a fixed voltage or put a pot in series with R2 (see below link) to be adjustable.

The GTI connector is a .1" center connector, so are most of these portable phone battery connectors. The fan connector is also a .1" center type, but has 3 pins typically. It is possible to take a razor blade and carefully cut the fan connector to fit the GTI connector.
I put a dallas temperature sensor on the Grid Tie Inverter and logged it. It has been doing this same thing for over a year now. Full power output to the grid at 250W sometimes I see 260W, and you can see when it goes to constant output at about 9:30AM.

This is a cheap Power Jack 300W Grid Tie Inverter. The old model with the flat top.

This one has the 80mm fan blowing into the inside as described in the previous post. The small stock internal fan is disconnected.

Some people have said you can't run these at full output. Since the max temperature here is only about 79F, I think you can run them full out with the normal fan but mount them to a piece of metal.

Most MOSFETs are rated to operate up to 300F !

I have measured the efficiency of this one, direct amp measurement, and it's about 78% efficient at full output.

I'm also running this off of two big deep cycle 12V batteries (GTI at 24V), but that's another story.
See previous posts below for info on the external fan.

I put a dallas temperature sensor on a NEWER style Grid Tie Inverter and logged it for an hour. Ran it on 24V batteries.

This GTI was mounted to a vertical wood board, fan facing up. The sensor was clamped to the side using a plastic clamp so it wouldn't skew the results.

This GTI has no extra fan blowing on it and is not mounted on metal.

At one point in the chart you can see how the GTI shut down for some reason, it was only at 95.6F. One green light was on and did the quick short blink thing, fan was on but no output power for one minute. Like all machines, it would probably do that again over and over but this was only a hour test. I guess that is how they protect it.

Room temp was 65F and fan output temp was hanging around 86F (using a different sensor).

I also took voltage and amp readings every 10 minutes. Watts is output to the grid, read on the Kill-A-Watt meter.

Time Amps Volts Watts Temp Efficiency
 00 12.7A 23.5V 251W 65.0F 84.1%
 10 11.9A 23.2V 230W 88.0F 83.3%
 20 11.8A 22.9V 224W 92.7F 82.8%
 30 11.9A 22.6V 222W 94.9F 82.5%
 40 12.0A 22.4V 221W 95.6F 82.2%
 (shutdown happens in here for 1 min, fan output is at 86.5F)
 50 12.3A 22.2V 224W 94.0F 82.0%
 60 12.4A 21.8V 221W 96.0F 81.7%

Kill-A-Watt reads 200 Wh total to the grid. Should be 220 Wh but that's what it actually read.

Conclusion? Needs a extra fan blowing on the outside, even a slow movement of air would help. 96F is really not that hot for most electronics and mosfets can go much higher but they have programmed this device very conservatively, or it's possible that this particular one is a little sensitive. Consumer grade thermistors and resistors have a wide tolerance so it's possible that is the problem.

I have added a fan from a power unit that was burn after 9 years i hooked it up with a simple bracket and i control it with aux. controller thermostat switch for cars or trucks that use it for trans coolers or help out a/c systems run better when u add a aux. fan to the cars radiatror or trans. real well. These are fully self contained units u can get them at most auto parts stores for about $40.00. They made to handle big power like 40 amps or more. I have them in all my Rides. U can see this set up on Utube. Its good to cool these things off and its great when u can run off battery bank. See my video below starting at time index 1:06 to see the thermostat.
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