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Old 05-18-10, 08:41 AM   #41
Xringer
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Default 500 Watts

Quote:
Originally Posted by jwxr7 View Post
I bought and recieved a 500w grid tie inverter. I haven't had a chance to really test it yet. But I did a quick test and got 500w out of it thru my kill-a-watt, with 24v of battery connected to it.

I've pretty well got the arduino system tested and working, just need to do some test witht the inverter in the system.

I was just looking at the specs, and I saw the PV power limit..

Electrical Specifications:
Grid-inverter Type 500W
Recommended Maximum PV Power Ppv=720Wp
DC Maximum Input Power PDC.max=600W
DC Maximum Voltage VpvDC30.2VDC
PV MPPT DC Voltage Range Vpv 12.5V~28VDC
Peak Inverter Efficiency ηmax>94%
MPPT Efficiency 99%
PV Maximum Input Current Ipv.max30A


I'm just wondering how the MPPT 'brain' handles being connected to a battery bank??

It seems like a big 24V bank would appear like an almost unlimited
amount of PV is being used.. Unlimited current..?.
I know that a couple of old car batteries can pump out way more than 720 watts of power..
Will the MPPT try to suck those batteries bone dry?

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Old 05-18-10, 08:33 PM   #42
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My inverter definitely works with 120vac 60hz. Some grid tie inverters I've seen are auto sensing to work with both voltages and frequencies, not sure if mine is like that. I don't plan to try anything other than 120v 60hz though.

It is interesting to watch the mppt work on a battery, there are youtube videos of GTI tests with voltmeters and ammeters running. Like this (not mine and not large batteries either but interesting)


I know what you are getting at with the mppt and large battery question.

My thoughts are that the inverter isn't going to go outside of certain limits for input current and voltage, and output power. I tested mine with two 6v golf cart batteries in series (12v), and it puts out around 100w. This is what I was expecting, since it is on the low end of the input voltage requirements. I asked several sellers with different GTIs with similar spec, and they all claim to expect around 100w max with a 12v battery. When I tested with a small 24v set-up (18ah), I could see it work the current and voltage until it was putting out rated power, then it didn't rise above that power level. As battery voltage dropped, it asked for more current. I can't comment on 24v with large capacity batteries yet, but I'll soon try it.
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Old 05-18-10, 11:18 PM   #43
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When you do try those high capacity batteries, keep a close eye on the max watts. Just in case.

But, from the sounds of your 24V 18Ah test, it seems like the inverter is self-limiting.

As I think about it, it seems only logical to have the controller chip programmed with
power limits, to prevent things from getting too hot on those occasional perfect solar days..


I'm still thinking about getting some of those thin-film panels (54V~2A),
Kaneka Thin Film Solar Panel 110w
The price looks good, if they ship them by Ground.
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Old 05-19-10, 07:14 AM   #44
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Quote:
Originally Posted by Xringer View Post
Operating Voltage range: 12.5V to 28V Maximum input Voltage: 28V
Solar Panel: 30W minimum, only use PV panels with maximum power voltage at 17.5V.


That seems to really limit how high you can go with your panels or turbine..
How do you plan to feed this inverter?
I missed this question. Here's the plan so far;
I plan to have two 12v batteries, the arduino will be monitoring battery voltage and genereator current. When the battery voltage gets high enough (to be determined), it will use the GTI as a dump load until the voltage drops to a certain lower level, then it will disconnect the GTI and continue charging. If at any time the charge current goes above a set limit the arduino will switch the batteries from a 12v parallel set to a 24v series pack. This will allow the generator to provide the best charge power without overheating the windings. The GTI can recieve power from the batteries in either configuration. The generator will always be connected to the batteries in all modes. The batteries are a buffer and a storage device for the inverter. The wind is too dynamic to try direct connecting to this inverter.
I have decided to furl the turbine around 200w for now, to be on the safe side. This way, the GTI can always keep the batteries from over charging (here's hoping I need to worry about that). The generator really isn't rated above 8 amps anyway, so that is kind of my limit with a 24v system . I have made some heatsinks to put on the motor housing to help cool it, so I'll see if it can take more. There is a temp sensor in the motor I may monitor if I can come up with a graceful way of bringing the signal down the tower.
I have been looking at batteries and thinking more about the tower. Those are the things I'm really waiting on.

This is the plan for now anyway.
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Old 05-19-10, 08:17 AM   #45
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It sounds like you are going to be using some big relays. So, be aware of sparks, if you get any hydrogen.

Anyways, it's too early in the AM for me.. I'm not understanding where the PV is going to fit in.
When you get the circuit diagram done, I would be interested is seeing how the whole system is going to be wired up..
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Old 05-19-10, 08:51 AM   #46
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This wierd system will be all wind power for now. My PV array will stay running by itself for now.

I do have a 5w PV panel I could incorporate later if I want to add a trickle charge to the batts.

Last edited by jwxr7; 07-15-10 at 06:43 AM..
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Old 05-27-10, 06:52 AM   #47
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I have the batteries that I think will work. I bought an electric golf caddy at a yard sale for $5 and it came with a good 12v 33ah deep cycle wheelchair type battery . I found another similar battery at work that I'm borrowing for the 24v tests. I'll see if the boss will sell it to me.Click image for larger version

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The inverter will go up to full power off these batteries and hold close to 500w for a while. The problem I'm having now is with the inverter running too hot . It apparantly doesn't like to run at rated power off batteries for more than 10-15 minutes or so without going into overheat mode. I've been trying to thermally improve it by mounting it to a large heatsink with thermal grease, and adding extra heatsinking to the hottest area. This helped but I think I'm still going to have to add a small fan that blows across the hottest area while in 24v mode. At least it won't be using 24v mode as often as 12v mode (unless it catches more wind than I expect). Click image for larger version

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Old 05-27-10, 07:16 AM   #48
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To improve the efficiency of your fan setup you could use some ducting over the inverter. Use a small computer fan to suck air over the body. It could be as simple as some bent up cardboard and tape.
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Old 05-27-10, 09:02 AM   #49
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Default Heat sink design problem

It looks like the blades on top of the heat sink are too short and too close together.
And those on the sides should have been a bit longer.

If that big boy sink you added on the bottom is taking a lot of heat,
that would be the perfect place to add some well aimed air flow.

That bottom sink might be all you need, if the bottom floor of the
inverter is thick aluminum and the power transistors are mounted on that floor..
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Old 05-27-10, 11:33 AM   #50
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The bottom heatsink is taking away some heat, not as much as I'd hoped. There isn't a very thick path for the heat to conduct in that direction. That 'T' shaped one clamped on the side fin seems to get pretty hot. That's by far the hottest spot, where the high-current low-voltage power devices are mounted on the inside.

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