Current Limiting Device

[veggie]

Hi All,

Is there an inexpensive way to limit the amount of current supplied to an appliance?

In my case, a battery bank feeding directly to a Grid Tie Inverter (GTI).
The 24v - 55v  GTI is rated at 1200 watts max and is normally connected directly to 24 volt PV panels.
Typically one would have a 1000 watt PV array to drive this GTI so that the device can take all that the panels can give.
(If you push these GTI's to the limit they tend to cook their MOSFETS)

I would like to drive the GTI with a battery bank and I don't want to push a full 1200 watts into the GTI.
I would like to limit the current from the bat bank to 1000 watts.
How can I do this ?

thanks,
veggie

[glort]

If you wanted a real cheap and redneck way, you could do as I have done with DC current limiting.... Use a lightbulb for a resistor.

Here we have halogen tube floodlights that come in 500W. You can get 1000W as well but they are no where near as common.  You would have to figure out the wattage at the voltage you are using but if you hook a light in series with your inverter, you should be good and have a visual indication of how much power you are pulling by the intensity of the light.   

I'm sure there is a much more "Professional" way of doing this with the use of some electronic setup. Unfortunately, I can't help you with what that is but I look forward to reading the answer from someone that can.

[Jens]

The lightbulb thing is a non-starter because it drops the voltage that the grid tie inverter sees.
Have you explored all the various settings on your inverter? I would think that anything short of the real low end units would have full configuration options including the amount of power that is fed to the grid. The options may not be readily documented - you might have to get the info from the manufacturer. Casually thinking about the building blocks of an inverter, current limiting would be one of it's built in functions to protect the output transistors and the grid so it would make sense that this parameter is adjustable. Note that I said 'casually thinking' - no brain cells were exercised to the point of possible injury!

[mike90045]

I think only the hybrid / battery (grid tie/off-grid) inverters are programmable ?   I know my XW has programming for backfeeding certain amounts and lock-out times to never backfeed.

[BruceM]

A current limiting chopper circuit would do the job, since the inverter is doing MPPT, and would lower the output with dropping voltage input.  Meanwell does have chopper type current regulators, and voltage plus current regulators; perhaps these might do the job.

Two chopper type circuits in series (the Meanwell and the inverter) is a bit unpredictable, and I know that the Meanwell products are of very poor design, single sided boards, little or no concern for radiated emissions.  One or the other chopper may make the other go unstable.  So I don't think this is necessarily a "plug and play" solution.  It would be an experiment.

Best Wishes,
Bruce

[mike90045]

 Guess you will have to try out voltage limiting, and see if the MPPT circuit will accept it.     But the other factor is the "grid-TIE" part  -  it's going to be looking for the grid, and wants to sync to a 60.000Hz with near infinite impedance, and if you use a small inverter to "qualify the grid" you still will have trouble as it try's to pump power to the gird @ 250VAC  GT inverters are for the grid, not appliances.
  And they should in software, limit themselves to just their rated current, and if they begin to overheat, throttle themselves back more to keep the heat under safe limits. 

Is this a "plug-in" GTI from china, or a hardwire 400VDC string inverter ?

[veggie]

Is this a "plug-in" GTI from china, or a hardwire 400VDC string inverter ?

Hi Mike,
Its a plug-in GTI from China. It has island protection and switches off if the grid goes down.
My 600 watt GTI connected to a PV array has been pushing power into my home for 6 months. Works great.

I now want to drive my 1200 watt unit from a battery bank during peak hours. (the bank is charged by the Lister).
I fear that connecting the 1200 watt GTI directly to the bank will result in a full 1200 watts flowing into the GTI.
I do not want to run it at full capacity/amps. I want to feed it a max. of 1000 watts.
Putting a light bulb in the circuit would be a waste of battery power.

veggie

[BruceM]

Hi Veggie,

Here's my thinking this morning:

It might be easier and more efficient to add a boost fan for improved cooling on your grid tie inverter.  Check out their design carefully first, then see how to boost the airflow.  Any heatsink you can't hold your finger on is too hot and needs more airflow.  (Switch it off for that test after a run at full capacity.)  If the design is marginal at it's top rated power, this is how I would deal with the problem, rather than add  current limiting.  Adding a current limiting regulator ala Meanwell is going to cost you 15% efficiency.  Adding some more cooling is cheaper and more efficient.

Best Wishes,
Bruce

[veggie]

Good idea Bruce, Thanks !

veggie