Load leveling of an ST head

[squarebob]

Equipment:

GM 90 6/1
150 amp 24V alternator with Balmar 624 regulator
7.5 ST head wired for 120v on two legs
24v battery bank with Trimetric 2025 monitor
2500W inverter

This setup is for emergency hot water and power for the fridge, freezer, a few lights and a laptop. I want to install a transfer switch between a distribution panel and the 2 power sources, the inverter and the ST. When the batteries get to around 40 to 50% DOD I will start the 6/1, the alternator will begin to charge the batteries and the transfer switch will shift the loads from the inverter to the ST. Sounds like a good plan but this setup will only pull from one leg of the ST. How do I set this up to even the load on the ST head and pull from both legs. Or is that not that important with such a small load on the ST.

Another option would be to scrap the transfer switch idea and just keep the inverter as the primary power source 100% of the time and use the ST head, for a future well pump and to run the washer/dryer or other big loads during battery recharge time. Any ideas?

Bob

[Ronmar]

You could use a large isolation transformer, 240V-120V to power that large single 120V load.  These are readilly available for power conversion for running US spec 120V appliances on European spec 240V line voltage.  That is what I have setup for my microwave oven.  It is the single largest 120V load I have and really puts a hit on one leg of my ST-5 when I am powering my other basic needs.  The transformer spreads this load across both 120V legs(240V)...

[mbryner]

Easy answer for me.   Keep the clean beautiful power from the inverter and use the ST to charge the batteries only.  Less complicated and less to go wrong.   Wire the ST head for 240 V and keep it available only for emergencies if the inverter fails and for the well pump.   Your load will be evenly distributed if wired for 240.

Marcus

(I'm off grid and rectify the ST output to DC, then charge batteries via a solar charge controller.   The only power the house sees is from the inverters, never from the ST except if part of the system fails.)

[Tom Reed]

Maybe I've missed the obvious here, but why not just wire the ST for 120v AC output. Mine was wired that way during construction of our home and it worked really well to power almost all the big loads that the subcontractors came up with. It eliminated the growl that the ST heads make when powering an unbalanced load too.

Another choice is a load balancing transformer. Outback sells one and the schematics are available on line.

[sailawayrb]

Like Tom indicated, it you wire it for 120 you don't have to do anything and you will always be balanced.  Furthermore, you will also be able to apply 100% of rated power to both sides of your panel...and hence, also be able to apply 100% of rated power to any single 120 circuit.  If you wire for 240, you will need a transformer to maintain balance.  If you wire for 240 and don't use a transformer, you can only apply 50% of rated power to any single 120 circuit.  Of course, if you NEED 240, you have little choice but to have to deal with the aforementioned issues.

Bob B.

[mbryner]

Oops.  Must clarify.   My recommendation for leaving it wired for 240 V for balanced loading only applies if you are charging batteries using a transformer or MPPT charge controller or alternater w/ regular AND ALL your other loads are 240 V.