generator assist for off grid solar/battery system

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Old 11-11-11, 08:16 PM
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generator assist for off grid solar/battery system

I have a small off grid hunting cabin i have been powering with 60 watts of solar panel to charge a bank of two marine deep cycle batteries to run some cfl lights charge phones and rechargable screw guns, etc. All my lights and outlets are on one circuit.
I added a shower this year and acquired a small (10 gallon) 110 volt water heater. Not surprisingly the power inverter wont run the heater, but my (pre-battery) generator will. I want to switch power sources from battery inverter to generator when heating water and/or charging my batteries with an automotive battery charger. I'll probably dedicate a separate circuit to the water heater, but would like the option to run the whole cabin by generator.
Will I damage my 3000 watt (not pure sine wave) power inverter by running my 5000 watt at the same time on the same circuit?
 
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Old 11-11-11, 09:13 PM
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Yes. You need to disconnect from the inverter, then connect to the generator.
 
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Old 11-12-11, 05:04 AM
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Thanks Bill,
I saw some fancy breaker box interlock (lock-out) switches when net-searching this issue that seem fool proof to permit only "one or the other" to be the power source. Are those switches widely available? or are they internet only accessible? I'm familiar with the manual interlock switching devices for home use ($150), but hope to utilize something less expensive for this occasional use application.
It looks like I would need a breaker box with a "main" switch that can be turned off then simply insert a high enough load-rated breaker to cover the anticipated max load to serve as the alternative source. Am I understanding this correctly?
 
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Old 11-12-11, 05:22 AM
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A neighbor in Costa Rica lives off the grid and uses solar, hydro and backs up with a gasoline generator. He basically has monster sized blocking diodes or a device that allows the current to flow in only one direction so he can operate the solar, hydro and generator at the same time. Inside the house there are separate DC and AC circuits. DC is supplied from the batteries. The AC circuit has a transfer switch so it can either come from the inverter or generator.

I have made a simple interlock device for someone (outside the USA's I'll sue you culture) that works quite well. It is a funky shaped piece of 1/8" thick aluminum mounted to the face of the electrical panel. When the main breaker is on this lever prevents the first breaker (which is used to feed power into the panel from a generator) in the stack from being on. I'll look to see if I have a picture.
 
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Old 11-12-11, 05:36 AM
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I'm actually a bit surprised I was able to find the photo so quickly.



As you can see the top left breaker back feeds the panel from the generator. To switch to generator the main breaker must be switched to off which moves the blocking arm out of the way to allow the generator breaker to be flipped on. If you try to turn the main breaker on it automatically pushes the generator breaker to the off position. The size and shape of the lever creates a generous dead space where neither breaker is in the on position to insure that both breaker can never be on at the same time.

The pivot is a simple bolt with a nylock nut and several flat washers to allow it to pivot with a bit of resistance. I remember making cardboard cut outs to work out the shape of the lever and sticking a small nail through to find a pivot point that worked.

---
Did you know that a 200 amp panel will fit in your checked luggage? And if the Costa Rican officials choose to search your bag they will put a stamp in your passport forbidding you from bringing new goods, in bulk into the country for six months.
 
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Old 11-12-11, 05:47 AM
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Thanks Pilot Dane,
Necessity is the mother of invention- What a brilliant idea! Thanks a million.
Bill
 
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Old 11-12-11, 10:39 AM
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Understand that Pilot Dane's "solution" is NOT UL approved and therefore NOT acceptable anywhere in our country where electrical installations are inspected by a governmental authority.

Further, the National Electrical Code requires that such interlock devices not be able to be bypassed. Some jurisdictions have interpreted that to mean any interlock device that can be defeated by merely removing the panel's cover is NOT approved.

In the specific installation being discussed so far in this thread I think that PD's solution is excellent.
 
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Old 11-12-11, 11:12 AM
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That is a COOL lever idea!

But the NEC would never allow such a thing as you are bypassing buying expensive products from all those manufacturers!
 
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Old 11-12-11, 04:31 PM
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Yes, thank you for pointing out that the simple lever would never fly in The USA and is against code and should never be attempted. If made incorrectly it can allow both the main line and back feed to be connected at the same time. A VERY bad situation.
 
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Old 11-12-11, 07:35 PM
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A 60a DPDT center off safety switch would be the safer but much more expensive solution.
 
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Old 11-14-11, 10:06 AM
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The reason that type of homemade transfer switch would not be UL approved is that it is not guaranteed to be break-before-make. Both breakers can be somewhere in the middle of their throw arc at the same time leading to the possibility that both could be energized. In practice it is probably a rare sequence of events that would lead to both energized. All approved interlocks require that both breakers are OFF before either can be turned ON.

It is also possible the switch arm could jam the breakers in the ON position. Again unlikely, but without rigorous testing you really can't know if it's a safe installation or not.

Still, given the circumstance I think it's a good solution.
 
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Old 06-04-13, 09:09 AM
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Siemens & Murray Interlock Kits

If you have a Siemens or Murray CB Panel with standard 1" breakers, then you can order from Amazon.com, a choice of interlock devices starting at ~$18 (price varies periodocally) made by Siemens.
ECSBPK01 is made for stab-mount stand-by and main breakers across from each other ($22.34),
ECSBPK02 is made for stab-mount stand-by and main breakers next to each other ($22.64),
ECSBPK03 is made for stab-mount stand-by and 150-225A Main breakers ($52.97),
ECSBPK04 is made for stab-mount stand-by and 100-125A Main breakers ($55.80),
ECSBPK05 is made for stab-mount stand-by and QNR- or MD-TR 150-225A Mains ($15.22),
ECSBPK09 is made for two 200A Mains used in specific Meter-panels where the mains are 4-pole ($68.28).

The point here is, Amazon has lock-out kits that are OEM-made, UL-approved, reasonably priced, and EASY to order.

I suspect they may carry similarly-priced models for Square-D Homeline and QO-series breaker panels. Amazon.com: Online Shopping for Electronics, Apparel, Computers, Books, DVDs & more
 
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