Inverters Shutting Down

[Kevin Erion]

If Elliott's Marathon is like mine, and I will guess it is, the 270 amp alternator is 24 volt. This alternator only charges the house batterys. Marathon splits the house batterys up into 2 groups of 3 using 4D size batterys. The invertors are 24 volt and draw from there set of batterys. Just a little more info to help the brain trust! If this is of any help at all!

[Jon Wehrenberg]

That's a vital piece of information Kevin. If I interpret it correctly your inverters each have a dedicated bank of batteries and if Elliott had both inverters shut down I would be led to believe from that his problem relates to something common to both sets of batteries, perhaps they share a common ground.

As Elliott begins his quest to get info hang in there with us to keep our focus in the right direction.

[BenC]

Just to clarify, the house batteries are wired as follows on Marathon, Parliament, Vantare, etc: one group of 3 (or 4 for Vantare) is the "12-volt bank" and the other three are the "24-volt bank" with both inverters (through separate set of breakers or fuses) to the output bus bar or terminal of the "24 volt bank" and chassis ground. The output from the "12 volt bank" is there specifically and only to power the house 12-volt lighting and accessory loads, with a Vanner or Surepower battery equalizer between the 24 and 12v "taps" to make up and keep equally charged the "lower" or 12volt bank. The inverters do not, as such, have their own dedicated batteries. Hope that makes sense.

[Kevin Erion]

Thanks Ben, I was not sure and your explination helps me to understand my bus a little better!

[HarborBus]

Elliott, If I am screwing up here I hope Ben will jump in, but the voltage readings I would like to see are at the alternator output, at the batteries and at the DC input to the inverters. I would like to see you load up the electrical circuits in the bus that are on inverter, and make sure you are not on shore power.

As Ben described if you see a substantial voltage drop between what you see at the alternator, and what is going into the inverter that is likely your problems. If the circuit is unloaded there may be no voltage drop.

Conversely, if the voltage was high, and the inverters see voltage over some value (30 volts maybe) they will also shut down. At least my inverters will.

Here are the reading that Jon requested, these are take with one AC unit running, microwave on, drawing 115 amps. Engine at high idle at 175 degrees.

Alternator output: 27.74V
Measured at Batteries: 27.20V
DC imput at inverters:
Inverter #1: 26.91V
Inverter #2: 26.90V

[Jon Wehrenberg]

Elliott,

You sure do not have any over voltage issues. While I think the voltage drop is a little too large it is not alarming, but I would take the time to clean and re-tighten every DC cable and fitting from the alternators through to the batteries, all the way to the inverters. Don't forget the chassis grouinds.

I'm pretty sure you were not pulling 115 amps unless you are talking about DC at 24 volts. At 24 volts a heavy load on the inverters would be around 200 to 250 amps, or 40 to 50 amps AC.

[HarborBus]

Yes, I was referring to 115 amps DC on 24 volts. I know it wasn't a huge load but I couldn't run my front AC unit because the cover leaks and is on order, in the mean time I have it covered with plastic. What voltage drop would be acceptable? Is there a torque value on the battery connections I should be using or just clean and tighten them by feel? I know what the maximum voltage the inverters will allow before shut down is 30 volts, what is the minimum?

[Jon Wehrenberg]

I cannot answer the minimum voltage. The owner's manual should have that information.

An almost one volt drop to me seems large. If Ben is reading this I hope he jumps in with what he sees from his experience. Remember, the engine was running and the alternator was maintaining the voltage, yet it dropped between the alternator and where you measured on the batteries, and then some more to the inverter. You didn't say if you were on fast idle, but if you were I don't think there should have been that drop. If on low idle I think I could understand it because the alternator needs RPMs for output.

I had some goofy inverter actions recently and I found a number of the original cable and terminal connections that needed both cleaning and tightening. I would surmise you do not have a single point of problems, but more likely need to start at the alternator and just insure everything is clean, free of corrosion and tight. I cannot quantitatively define tight, but would expect to see it quite tight. I also coated all the connections with battery terminal corrosion protection after I got everything clean and tight.

[phorner]

As an aside to this general discussion, battery terminal and other electrical connections do need to be checked on a fairly regular basis.

I have a 72 volt electric car that has 6 wet cell batteries. I check the water levels at 3 to 4 week intervals and check all the terminals for corrosion and tightness at that time. It amazes me that almost without fail, nearly every battery connection that was tight less than a month ago will still allows a smidgen of tightening upon inspection.

I don't know whether it's the vibration from driving or just the nature of the connections but they almost always can use at least minimal torque to bring them fully snug...... until next time.

I wouldn't be real surprised if this was the case with all battery/electrical connections to some degree.

[HarborBus]

Here are the reading that Jon requested, these are take with one AC unit running, microwave on, drawing 115 amps. Engine at high idle at 175 degrees.

Alternator output: 27.74V
Measured at Batteries: 27.20V
DC imput at inverters:
Inverter #1: 26.91V
Inverter #2: 26.90V

Jon the measurements were taken with the engine at fast idle(see Quote). I will set about the task of disconnection all the cables one by one, clean and tighten. I appreciate the time you have taken to work through this with me. Additionally I also appreciate all the impute I have received from everyone else. I to hope Ben weighs in here before I have to undertake the removing cleaning and tightening of all the connections. I'm still at a loss for a definitive answer as to why the inverters shut down and I'm not really fond of the shotgun approach to a problem but sometimes it can't be helped. Ben where are you??