| Author |
Message |
Jason Whitaker (Jeepme)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 13, 2006 - 2:28 pm: | |
I installed my inverter (Xantrex Freedom 3000) in my bus this week and it seems to be working great. Will start up my 15,000 btu a/c just fine. I'm using Square-D QO circuit breakers for both the 12v and the 110v. Link 1000 controlling the inverter.
The problem I'm having is that I can't get the 15 amp breakers to trip when powered by the inverter. They will trip while on shore power immediately (pop!) but if the inverter is powering the circuit and I directly short the power to neutral or to ground it sparks a bit and the Link panel shows an increasing amp reading up until the inverter overloads and I get an overload error message on the Link. The 15 amp Square-D breaker never trips with a short.
I am wired up exactly as the inverter manual shows. I have a good ground from the inverter to the breaker box. (4ga) All neutrals are separate from ground, the inverter bonds neutral-grd automatically. I tried a couple of breakers, both act the same. This is with a direct short, I haven't tried to overload the circuit by plugging in a 20 amp load yet.
Maybe this is normal? It's just taking a second or two for the inverter to build up power and the inverter trips it's 30a overload faster than the 15a breaker can react?
Thanks everybody
Jason Whitaker
4104 |
Brian Brown (Blue_velvet)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 13, 2006 - 3:13 pm: | |
Jason, maybe you've done this already, but test your neutral/ground isolation with a continuity tester while unplugged from shore power, both with the inverter on and off.
Perhaps the inverter is not bonding as it should or you actually do have a bond somewhere. If current is running through the neutral legs and grounds without tripping a breaker, this is a VERY dangerous situation if you or someone you love becomes a path to ground.
A great test to check your isolation of neutrals and grounds is to plug the shore cord into a GFCI. If it trips, you have a rogue neutral bonded somewhere. This happened to me in my '06 when a rooftop A/C neutral had frayed into the frame of the bus.
Hope this helps, and keep us posted!
bb |
herman
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 13, 2006 - 4:50 pm: | |
While you should certainly recheck your wiring, I think that the cause lies elsewhere:
One big difference between inverters, gensets, and the grid is their impedance, or internal resistance.
The grid has very, very, very low impedance: for a given change in the amount of current you draw from it (or try to feed back into it, e.g. with a grid tied inverter), you will see very little change in voltage at your point of measurement. Much of what little voltage change you do see is due to the relatively small size of the 'local' wiring. So, the grid can source enormous currents into a short circuit.
Gensets and inverters have a very much higher impedance; the amount of short circuit current that they can source is correspondingly smaller.
In a genset, the time it takes to respond to a change in output current (also known as a "load step"; note that a short circuit is just a 'large' load step) is governed by several factors, including the mechanical inertia of its rotating mass and the response characteristics of the alternator's automatic voltage regulator and the engine's speed governer. The ultimate magnitude of short circuit current depends on yet other factors, e.g. engine power, alternator wire size and cooling (high temperatures increase wire resistance), etc.
These factors all vary from one make/model to another, and in good measure determine the quality of a unit's power. So, while a given unit will have a given base/continuous output power rating, it also has an instantaneous or surge rating that is some percent higher than the base rating; this percentage roughly correlates with power quality.
Inverters have analogous characteristics, e.g. the ampacity/impedance of the DC source, interconnect wiring, power switching transistors, etc. all influence short circuit current. An inverter's control electronics also influence short circuit current, and, more importantly to your query, almost completely determine the unit's response to load steps.
So, inverters also have surge ratings, which, when compared to base ratings, similarly separate the men from the boys, so to speak.
So, enough background. As regards your situation, you also need to consider the breaker. Square-D QO breakers have 2 trip mechanisms. One is magnetic, which provides for a very quick trip on shorts; the other is thermal, which addresses extended overloads of lesser magnitude than a short: it exhibits an inverse curve of trip delay vs. amount of overload.
What is happening here is that, when on the grid, your breaker is magnetically tripping in response to the enormous currents that the grid is pouring into your short. When using your particular inverter (as installed with your given battery bank and cabling), the combined system's surge capacity / load step response characteristics is insufficient to magnetically trip the breaker, and the inverter itself just happens to trip before the breaker thermally trips. |
Crane
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 13, 2006 - 4:54 pm: | |
If that is a NEW Xantrex Inverter, I would hasten you to read the restrictions on the Warrantee.
If I recall correctly, they EXPLICITLY name shorted wiring causing damage to the inverter as a VOID on the warranty.
as for the trip problem, GFI is the name of the game.
I am thinking you are using a Mod sine wave and it affects the breakers differently because you don't have a true sine wave. You don't have DC either but there is a cause and effect involved there.
My thoughts
Crane |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 13, 2006 - 7:25 pm: | |
Did you check the output voltage when subjecting the inverter to an overload? I suspect the voltage may be dropping considerably which in turn would reduce the current.
It would be good to check amperage also with a clamp on ammeter.
That is the only sure way to really know what is actually happening.
Richard |
Tim Hoskinson (Tdh37514151)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 13, 2006 - 9:04 pm: | |
Jason all inverters I have ever worked on have dc current limiting circuits that do not alow high current to flow in the inverter switching device be it IGBT or darlington transistor what ever may be used. This electronic current sensing circit will respond to the high level of current that takes place with a short circuit at a much faster rate of time than the circuit breaker can possibly respond. Most inverters will lower the out put voltage in order to limit the current to the level needed to protect the switching device. This will take place and you may not be notified by the machine's alarm until long after it has taken place. If the inverter did not do this by the time the breaker kicked the inverter would most likely be destroyed. As already stated don't temp fate by continuing to short the out put of a inverter as you will at some point damage it. Even current sensors can not protect against back fed arc energy. Best of luck Tim |
Kevin Hatch
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 14, 2006 - 12:15 am: | |
So are you guys saying that if I plug into a GFCI shore outlet and it tripps, then I've got problems? Because when I first got my bus I tried plugging it into a GFCI outlet behind the house and it tripped immedatly. Then I tried a regular outlet in my shop and it works fine (granted it is a 30A circut). I figured the GFCI was just too light and tripped too easy. |
Jason Whitaker (Jeepme)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 14, 2006 - 1:43 am: | |
Tonight I checked the ground-neutral bond with the bus unplugged and it was bonded at the inverter. Then, since I didn't have a gfi outlet nearby, I went and risked my life by digging up one of those cheap two wire extension cords and plugging the bus in with no ground. The ohm meter said gnd and neutral were separate. So I don't have a problem there.
Thanks to all of you for the help!!
Guess I should have asked quicker instead of subjecting my inverter to inverter hell.
Kevin, you may have a problem. Sounds like you have a neutral and ground tied together on your bus. Do a search in the archives, there are some good explanations there. One thread 'electrical shock' explains the dangers pretty well.
Thanks,
Jason Whitaker
4104 |
herman
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 14, 2006 - 2:26 am: | |
Kevin,
If your bus trips a GFCI breaker then You Have A Problem - it's not a question of 'how easy' the GFCI trips.
Jason,
It sounds like you know about bonding; I'm just going to elaborate for sake of edification of others.
You are describing correct wiring: When on the grid, the ground-neutral bond is not within the bus, but externally, at or upstream of the shore power connector. When instead on onboard power, the bond is supposed to be located at the power source, i.e. either genset or inverter.
In other words, there should always be exactly one bond in effect, and it should be located at the current source. To achieve this, it is generally necessary a) to have a permanent bond at the genset, b) for transfer switches to handle not only the hot pole(s), but also the neutral, so that the genset bond can be rendered moot when the genset is not in use and c) to use a relay to effect a bond when on inverter power. |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 14, 2006 - 9:15 am: | |
Here are a couple of links with lots of electrical information:
http://www.phrannie.org/phredex.html
http://www.purplebear.com/busnuts/bus_elec.html
Richard |
Kevin Hatch
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 14, 2006 - 7:21 pm: | |
I know for a fact the grounds and neutrals are tied together at the bar in the power switch and maybe also at the breaker box. I didn't know any different for the bus. How do I seperate the ground and neutral? |
herman
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 14, 2006 - 7:47 pm: | |
Kevin, you need to provide much more information.
What bar or bars - the neutral bars? What power switch, what breaker box? In your house or your bus?
In your bus: Do you have a single main panel or multiple panels? Where is the inverter? Do you have a genset? A transfer switch? How are all these components interconnected, i.e what is the topology of your system? |
Kevin Hatch
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 14, 2006 - 11:22 pm: | |
OK here's what I have. Generac 7.5KW genset hooked to a two pole automatic transfer switch. The shore power goes through the other side of the switch. The transfer switch feeds to a small two breaker box. That then feeds throughout the bus. There's no inverter at this time. I'd like to ad one but can't afford it now. This is how the bus was rigged when I got it. The only thing I've done is install the new genset, and wired it back the way the old one was. |
herman
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 15, 2006 - 2:46 am: | |
"The transfer switch feeds to a small two breaker box." Yup, that's pretty small, alright!
You're gonna love this, but I still need more information. Sorry to be so demanding, but there's a couple gazillion ways that one can wire things up, and only a very few of those are proper/safe.
What are you using for a shore cord: a 120V, 30A, 3-wire cord or a 120V/240V, 50A, 4 wire cord?
Is the genset set up for 120V/240V service (typical), or straight 120V service? If the latter, how many hot wires feed into the transfer switch?
How exactly is the transfer switch wired to the sources?
How exactly is the transfer switch wired to the breaker panel?
What kind of breaker panel is this, with only 2 breakers? A proper breaker panel has 1, 2, or 3 hot buses (for 120, 120/240, or 3 phase service, repsectively); the feed into the panel either connects directly to the bus(es) via lug(s), or indirectly via a 1, 2, or 3 pole service entrance breaker. While the shore box has breakers, as your genset also needs to have, I personally would use a service entrance breaker in my panel nevertheless.
It sounds like this box is not a breaker panel, but a service disconnect box, such as you might find outside a house feeding a central A/C unit. In such a box there are no busses; the feed hot(s) go directly to one side of the breaker, and the load hot(s) come off the other side of the breaker.
So, what kind of box is this, exactly? Are there 2 breakers or a single 2-pole breaker? What is/are the rating(s) of this/these breaker(s)? How is it wired to the transfer switch and the loads?
It sounds like you have a serious deficiency in this area.
As for the bonding:
The way it needs to be set up is to have a bond at the genset itself, and nowhere else in the bus. The transfer switch should be switching all the hots and the neutral; this way, when on shore power, the bond at the genset is disconnected, and the bond at or upstream of the shore connector box is the active one.
So, if you are running 120V on a single hot wire, then a 2 pole transfer switch is ok; one pole for the lone hot, and the other for the neutral. If you are instead running 120/240 service, then your transfer switch needs to be a 3 pole model.
From your earlier post, where you said that the neutrals in the switch box went to a bus bar, and given the size of your genset (30A on each of 2 legs if set up for 120/240V (typical), 60A on a single leg if set up for 120V only service), it sounds like your stuff is set up for 120/240 service, with the transfer switch handling only the hots (you might have a 30A shore cord that feeds both poles of its side of the transfer switch). |
Kevin Hatch
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 15, 2006 - 8:30 am: | |
Honestly I can't remember off the top of my head exactly how its wired. I don't have the bus here to look at either, it's at the mech's shop right now. Hopefully he's done with it early next week and I can investigate further. Sorry I'm not an electrician. I know the basic kind of stuff.
If my memory serves me right, I think there were 2 hots and 2 neutrals and a ground coming from the genset to one contactor in the auto switch.
I cant for the life of me remember how the shore cord is wired, but it goes to the other contactor in the auto switch.
It seems like i remember 5 wires going over to the two breakers which are 30A.
From that point I haven't ever looked to see how they wired it.
When I get the bus back, I can take some pictures and e-mail them to you.
Thanks |
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