# Grid Tie/Interactive Problems

Registered Users Posts: 7
Hello,

We just installed a flexmax80 along with a gvfx3524 inverter and a battery bank. The flexmax80 works fine with the inverter. However, when we attach the inverter using AC in to the grid it works for sometime (8 minutes) and then trips the breaker between the batteries and the inverter. No problems with AC out. This has been happening repeatedly. Is there someone who has experienced the same problem? Any suggestions will be appreciated.

Re: Grid Tie/Interactive Problems

What size circuit breaker? How long is the battery:inverter wire run and what gauge is it?

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 7
Re: Grid Tie/Interactive Problems

The circuit breaker is 80 amp dc and the wire gauge 2 and is approx. 7 feet in length. The battery bank is a 24volt system. The AC panel end of the AC in wire goes through a 60 Amp AC breaker. Thanks for your help.
Re: Grid Tie/Interactive Problems

How much GT power / off-grid peak power do you expect to output/use?
• 80 amps * 24 volts * 0.80 efficiency = 1,500 watts
If you pull more than 1,500 watts, you are getting close to the maximum you could draw from the battery bank / circuit breaker before tripping.

If I was defining the minimum wiring/breaker/fuse for full power operation of a 3,500 watt 24 VDC inverter:
• 3,500 watts * 1/21 volts batt cutoff * 1/0.80 invtr eff * 1.25 NEC safety margin = 260 amp @ 24 VDC circuit rating minimum
I may be misunderstanding your requirements/needs--but it sure sounds like you are under designed for the DC 80 amp breaker and a 3,500 watt inverter.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 7
Re: Grid Tie/Interactive Problems

Bill,

The whole system has been working fine for over 3 months. Problems started only when we hooked up the AC in connection. Right now the inverter is working fine (with the AC in breaker off) and running 3 fridges all the time and the basement bathroom lights including the upflush motor (intermitantly). I have not altered the battery bank in anyway. My system is 1 kw.
Re: Grid Tie/Interactive Problems

Only thing I can think of is if something lost it programming--Or if this inverter has an internal charger--it is drawing more than 1,500 watts from the AC line to charge up the battery bank...

Circuit breakers can fail and false trip... If you have no indications of high current flow, it may just be a bad breaker.

That is about the limit of my knowledge.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 246 ✭✭
Re: Grid Tie/Interactive Problems

The breaker from the inverter to the batteries should be 250A DC, The wire size 4/0 or 120 mm ish, The charger will start a charge @ 85 ish amps when you connect AC in, An 80 amp breaker will take a while to go out at that, ( you should have 80a breakers either side of the FM)

Have a good one
Tim
• Registered Users Posts: 7
Re: Grid Tie/Interactive Problems

Hello BB and Blackswan555,

I will purchase that 250breaker right away. Thank you both for your prompt help. This forum is very helpful.
• Solar Expert Posts: 246 ✭✭
Re: Grid Tie/Interactive Problems

Be sure to upgrade the wire size also , those inverters can easy pull 200 + amps ! If you need more specific details on setting it up to sell may also be worth an ask over on the outback forums http://outbackpower.com/forum/ they also have live help accsesable at the top of the page, ( IIRC 9pm > 1AM CET)
Have a good one
Tim