wiring pure and msw inverters together?

[BB.]

The Xantrex includes a transfer switch (generator/inverter)... That would work very nicely when you need to use the genset to recharge your battery bank or provide more power than your bank can supply.

By the way, have you tested the DR with your genset to make sure it charges your battery bank? Some Inverter/Chargers don't like gensets with wondering frequency (don't know anything about the DR specifically--just a common issue with some some inverter/chargers).

Yea--it is kind of hard to find a cheap two pole transfer switch (two pole transfer switch required for use with MSW inverters--you should not even share the AC neutral line either).

-Bill

[icarus]

The Suresine 300 is a great little inverter.

Tony

[Cariboocoot]

A caveat in case this issue was missed or forgotten:
If you're going to have an MSW and a TSW inverter sharing AC neutral (as with a common AC box) there must not be a neutral-ground bond on the TSW inverter or else it too will be "shared" with the MSW inverter, and they don't like that (to put it mildly). Keep both AC outputs completely isolated from one another is, in my opinion, best.

[icarus]

Noted in post #4 but never an issue to reenforce a critical issue.

Tony

[Paul54]

I have been using double pole double throw AC coil relays to do change over of selected house loads. My inverter, a no name Asian import, is a true sine but does not like it's neutral grounded. I come out of my main grid breaker panel and break the branch circuit with the relay. The normally closed contacts are the grid power with the wiper arm being the branch circuit. The normally open contacts are the inverter feed. The AC coil is fed with the inverter's AC output. The result is that when I turn on my inverter it automatically pulls in the relay coils and switches the branch load circuits to inverter power. When I shut the inverter down it automatically drops back to grid power. I have a switch in series with each coil that lets me "arm" or disarm each individual branch circuit. The relays being double pole, switch both the hot and neutral legs of the branch circuit. This also isolates the grounded house neutrals from the inverter. Like others have stated before, you must keep the neutrals isolated. When I was putting in this system, I "accidentally" found two branch circuits that were sharing neutrals downstream of the breaker panel. Whether you build your own transfer switch or buy one, carefully check that each branch circuit is truly isolated, that no hots or neutrals are shared or no neutrals have been grounded downstream of the breaker panel. A good quality relay with 20 Amp contacts is about twenty bucks. You can add them one at a time as needed. They work well for adding multiple inverters to your house circuits. But remember, when mixing inverters and or grid power, complete isolation is the key.

[summitdweller]

I know it has been awhile I sort of understand the neutral ground idea. So if I have one inverter the suresine 300 go to the transfer switch and the msw also go there, turn off the not used inverter, transfer to the right (on) inverter then go to the single ac breaker box to power all circuits will this work or does the neutral ground issue come into effect? The ground for the system is from the breaker box to ground no where else. Also what size inline fuse from batteries to suresine300?

Thanks I need to do this as now I have a computer that hates the msw.

[Cariboocoot]

The short version is if the MSW inverter has either output wire connected to any wiring that is bonded to ground anywhere it can go up in a puff of smoke.

It is perfectly normal for the one and only neutral-ground bond to be in the breaker box. The MSW inverter doesn't care where it is, it only cares if it makes an electrical connection with it and ends up feeding high Voltage back into itself (because the case is often bonded to negative and/or the negative to ground).

The only way to prevent the trouble with a transfer switch is if the switch changes both hot and neutral and the neutral-ground bond is on the output of the sine wave inverter and is not part of the AC wiring if the switch is set for "TSW" input rather than "MSW" input.

Usually a computer doesn't care about the quality of its input Voltage as they have great power supplies. The same can not be said of monitors, however. If you have an inverter that actually messes up a computer, get rid of it; it must be awful junk.

The MS 300 Watt inverter uses about 30 Amps max on continuous but can draw up to 60 under surge conditions. As such, the manual calls for a 100 Amp fuse or breaker.

[BB.]

I am not sure--You want to have a transfer switch between two inverters as sources (MSW and TSW)?

I would probably just wire a separate circuit (if you can) from the TSW to the loads you want on the TSW inverter.

Regarding grounding... Technically, the "problem" with most MSW inverters is if the battery is grounded and the AC "white wire" is also grounded. That will cause a short circuit through the middle of the inverter--and possibly ruin the MSW inverter.

So, you could "float the battery bank" (both + and - leads which now become "hot" with respect to ground) with the MSW inverter white wire grounded--However, not recommended. Many things assume that the battery bank is ground referenced and you could, for example, get the metal chassis of the inverter "hot" (if it is connected to the battery "-", or if you have RT 232 communications between a 12 VDC device and something else, etc.).

So, nominally, for the MSW inverter setup. Ground the battery negative terminal and float the two AC wires (both are now "hot").

If you have the AC home wiring now floating (no grounded neutral), you can connect the TSW inverter through a (recommended) two pole transfer switch (with the MSW on the other set of connections) and power everything relatively safely.

For most TSW inverters, you can ground one of the 120 VAC outputs and call it "white"/"Neutral". As always read the manuals in detail.

Regarding fusing, the manual should have the DC fusing requirement, but the back of the envelope calculation would be:

• 600 Watts max power * 1/0.85 invrt eff * 1/10.5 battery cutoff * 1.25 NEC fuse/wiring/breaker derating = 84 amps minimum

And round up to next standard wire/fuse/breaker sizes.

-Bill

[inetdog]

The short version is if the MSW inverter has either output wire connected to any wiring that is bonded to ground anywhere it can go up in a puff of smoke.

It is perfectly normal for the one and only neutral-ground bond to be in the breaker box. The MSW inverter doesn't care where it is, it only cares if it makes an electrical connection with it and ends up feeding high Voltage back into itself (because the case is often bonded to negative and/or the negative to ground).

Every time I see this kind of reference, I cringe. What is actually happening is that the output is being shorted out, as BB stated. There is no "feedback of high voltage" involved at all.
The results are what count (magic smoke being lost from the inverter) but the terminology counts in recognizing the problem and finding a solution (if any).
It is, however, true that if the battery is not grounded and so the system does not smoke, but the MSW output "neutral" is grounded, there will be high AC voltage to ground on the battery leads and perhaps on the case of the inverter. In that limited sense, the AC is "feeding back." And the magic smoke may be emitted by you instead of the inverter.

[Cariboocoot]

Every time I see this kind of reference, I cringe. What is actually happening is that the output is being shorted out, as BB stated. There is no "feedback of high voltage" involved at all.
The results are what count (magic smoke being lost from the inverter) but the terminology counts in recognizing the problem and finding a solution (if any).
It is, however, true that if the battery is not grounded and so the system does not smoke, but the MSW output "neutral" is grounded, there will be high AC voltage to ground on the battery leads and perhaps on the case of the inverter. In that limited sense, the AC is "feeding back." And the magic smoke may be emitted by you instead of the inverter.

Every time I see this kind of reference I cringe.
Shorted output to input; output is higher Voltage; inverter fries.

The next person who insists on explaining things in a complicated way to someone who wants a simple answer (newcomer) is going to get the Nac Mac Feegles sent to his house!