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Old 07-28-2016, 01:33 PM   #1
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Cheap Centech Inverters. Stackable?

I have a pair of Centech (yeah ... I know. Harbour Freight) 2000/4000 inverters.

Does anybody know if they are "stackable" ... or if their 120VAC hots and commons can be joined together at appropriate bus bars in the AC panel?

http://legacy.outbackpower.com/pdf/t..._Explained.pdf

1. After all I've read, I'm pretty certain that all the GROUNDS can go to the chassis.

2. After all I've read, I THINK I want to join all the commons from the inverters to one leg of a transfer switch which will lead to the common bus bar in the AC Panel. The other leg of that transfer switch will be fed by the output from the transfer switch for the common from Shore Power and Generator.

Refer to the WONDERFUL diagram from Familywagon found at the top of page 16 of this thread: http://www.skoolie.net/forums/f10/ho...ac-448-16.html

Thanks!

T
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Old 07-28-2016, 04:55 PM   #2
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If it were DC voltage, you might be able to get away with it - like running batteries in parallel.

But you're dealing with alternating current, meaning the hot wire could be anywhere from about 150 V to about -150 V (roughly - it comes out to 120 volts or so when it's kinda-sorta-averaged). So you could spectacularly blow things up if it happened to be off just right, or merely start a fire and have minor explosions if it were just a bit off.

If I'm understanding your question. Others may wish to chime in.

HOWEVER, you could certainly use one inverter for the front half of the bus and the other for the back half. Or left and right. But be sure they're separate all the way back to the inverter.
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Old 07-28-2016, 05:08 PM   #3
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The only way you can "stack" the AC side of inverters is if they are grid-tie inverters. Those sense the phase of the AC wave and sync them together.
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Old 07-28-2016, 05:11 PM   #4
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Quote:
Originally Posted by Tedd View Post
2. After all I've read, I THINK I want to join all the commons from the inverters to one leg of a transfer switch which will lead to the common bus bar in the AC Panel. The other leg of that transfer switch will be fed by the output from the transfer switch for the common from Shore Power and Generator.
After re-reading this, I see I've made a HUGE error. It should read:

After all I've read, I THINK I want to join all the HOTS (Black Wire) from the inverters to one leg of a transfer switch which will lead to the HOTS (Black Wire) in the AC Panel. The other leg of that transfer switch will be fed by the output from the transfer switch for the HOTS (Black Wire) from Shore Power and Generator.


Here's the diagram I referenced earlier.:


Quote:
Originally Posted by family wagon View Post
Since there haven't been any other replies, I'll take a swing. Here's a block diagram for "some day." Protection devices (fuses, over-current/arc/ground-fault breakers) are omitted for clarity.
ALL of the commons would go to the common bus bar ... all of the grounds would go to the chassis.
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Old 07-28-2016, 05:26 PM   #5
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Originally Posted by Dapplecreek View Post
If it were DC voltage, you might be able to get away with it - like running batteries in parallel.

But you're dealing with alternating current, meaning the hot wire could be anywhere from about 150 V to about -150 V (roughly - it comes out to 120 volts or so when it's kinda-sorta-averaged). So you could spectacularly blow things up if it happened to be off just right, or merely start a fire and have minor explosions if it were just a bit off.
I'm definitely into trying to avoid a fire.

I am pretty sure that I could do it with VDC. In a VDC circuit, if I connected everything in series, I wouldn't be messing with volts ... I'd be increasing amps. I'd have to up the wires to handle the load ... but otherwise ... no problem.


Quote:
Originally Posted by Dapplecreek View Post
HOWEVER, you could certainly use one inverter for the front half of the bus and the other for the back half. Or left and right. But be sure they're separate all the way back to the inverter.
Yeah ... that's kinda what I was afraid of.

Unfortunately, I want to work shore power and power from the genset into the system. I fear a setup like this would require TWO transfer switches and TWO VAC panels. Messy and complicated.


Lets see what other VAC mavins have to say ...
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Old 07-28-2016, 05:32 PM   #6
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About stacking inverters, I included this in my first post:

http://legacy.outbackpower.com/pdf/t..._Explained.pdf

This .pdf seems to suggest that inverters CAN be stacked ... but VAC is tricky and not something I deal with alot ... I'm a DC kinda guy. The ,pdf could be total BS, after all, I found it on the internet!

I figured I'd throw it out here to the experts.
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Old 07-28-2016, 06:47 PM   #7
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Yes, some inverters, even non-grid-tie inverters, can be stacked. Consider parallel-capable inverter-based generators and this "GTSUN" inverter I dug up on Amazon. Unfortunately it doesn't seem to be a very common feature.

The suggestion from Dapplecreek to divide the bus so that each inverter handles only part is interesting. If you had just two inverters, you could use a conventional 120/240 volt breaker panel for the distribution and wire one inverter to each hot leg in that panel. It would only add one more switch to the diagram quoted earlier. Add a switch for the second inverter, just like the one shown between the first inverter and AC panel. The "upstream" side of the two switches, going to the shore/generator selector, could be tied together. In this way the two hot legs in the panel would be isolated when fed from inverters, but tied together when fed from other sources.
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Old 07-28-2016, 07:41 PM   #8
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Quote:
Originally Posted by family wagon View Post
... you could use a conventional 120/240 volt breaker panel for the distribution and wire one inverter to each hot leg in that panel....
But if you do that, whatever you do, DON'T TRY TO ADD A 220V BREAKER! And I would worry that the next owner might try it... this is why we have codes, and why we all should at least be within horseshoe distance of 'em - or better. Prevents time bombs.
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Old 07-28-2016, 08:11 PM   #9
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It's an interesting thought exercise to wonder what might happen if one did try to use a two-pole/240v breaker.. when connected to the shore/generator power with the two hot legs tied together the load wouldn't do much of anything. Supposing it were a range, oven, or clothes dryer, then the controls might come on but the appliance wouldn't heat. On the other hand, when supplied by the inverters whose phases aren't synchronized, the controls would probably power on as before and there'd be some heat but not so much as would be expected. It would vary from full heat to no heat as the phase difference between the inverters varied. A resistive heater might not mind that so much, but if instead the load included a 240 volt motor then operation would be strange and possibly damaging to the motor.

I agree that it's non-conventional and would require leaving something written in the panel to explain the situation. On the other hand it does avoid having two breaker panels (which can have its own set of "I thought I turned off all the breakers!" problems). Also it seems 120/240 volt main lug load centers are much easier to find than the 120 volt-only type are.
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Old 07-28-2016, 08:58 PM   #10
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correct

Quote:
Originally Posted by ashandrik View Post
The only way you can "stack" the AC side of inverters is if they are grid-tie inverters. Those sense the phase of the AC wave and sync them together.
By stacking you mean to tie the outputs together, correct?

These harbor freight (i shop there often) inverters and most others do not sync up.
One may be outputting a low phaze (-60v ) while at the same time another is outputtings a high phaze (pos 60) equalling zero volts. Surely they will be pushing and pulling on each other and destroy themselves and electonic attachments. It's a phaze thing, AC is complex.
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