Inverter shutdown

[Hayman]

Ditto, How long on average should the micowave be able to run off inverter/batteries, realizing state of charge dependent before the genset would start if enabled ?

[twinboat]

In theory a microwave drawing 15 amps AC, translates to about 150 amps, 12 volts DC.

A 8 battery bank should give you about 800 AHs.

Add in the losses thru the inverter and you should be able to microwave for 2 hours and not go below 50%.

[photraveller]

Has inverter always shutdown like this, or is this a new problem?

Do you have any idea how the tech capacity tested the batteries? I wonder if he load tested them to the same 110+ amps.

If capacity wasn't done under a large load, then I would suspect a connection issue. Either the interconnect cables, corrosion, or loose, or bad connection internal to one of the batteries. Since this is a relativity new coach I would suspect something came loose or broke.

If nothing shows up with the interconnect cables, then I would suspect a manufacturing issue with one of the batteries. Probably a cold weld where two pieces of lead are just touching each other not fully welded. When this happens, the pieces can become corroded and not allow the higher currents without a large voltage drop. While still passing the initial factory hi-rate testing that was probably in the 1,000 amp range.

Since its a AGM, it could also have a single cell that didn't get enough acid, and is partially dried out.

Since I believe you have four sets of 2 batteries in parallel I would try to get current readings from the interconnect battery cable between each set of 2 batteries. That will tell you if all four sets of batteries are producing they're share of the current. If one set is a lot lower than the others that will be an indication that something is wrong in that set of two.

Finally I would check the wiring diagram. If you have 8 batteries, then you have 2 batteries in series with four parallel sets of 2 batteries, correct? Make sure the leads to the inverter are not both tied to the same 2 battery set. The leads should be diagonal from each other. One lead on the first set of 2, and the other inverter lead on the fourth set of 2. Again this is something that might not show up under small loads, but under high loads you might be getting too much voltage drop across the first set of 2 batteries if both inverter leads are connected there.

However I would start with the current readings between the four banks of 2 batteries. Just make sure you are wearing safety glasses if you are standing there with a current meter while someone tries the microwave. If it's a battery issue, high currents through a bad battery can cause a battery explosion!

However I will say "most of the time" a battery "explosion" is nothing but a really loud noise maker and a little acid splatter. In other words, nothing that would prevent me from doing the test, but I would make sure my eyes were covered, they are the only thing other than your clothes that will suffer from a little acid for a short period of time.

Steve

[photraveller]

Twinboat, I agree that the battery capacity will be a long time, but it may be less than 2 hours for 50%. I know you have some fudge in there, but maybe not enough.

The 800AH rating was probably done at a 20 hours discharge rate. At these much high discharge rates, the batteries will perform well under their 800 AH rating.

Steve

[twinboat]

According to my understanding, with 8 batteries, the load is shared among them all.

An 8 battery bank will be close to the 20 hour rate at 160 amps draw.

Here is an explanation.

When you put two batteries in series the voltage will double but the amperage (amp hours or AHs) stay the same. The capacity of the bank doubles. If one battery can store for 1.24 kWh then 2 batteries can store 2.48 kWh. The amperage has not changed, the voltage has. Amps X Volts = Watts. Double the voltage and you will double the watt hours or kilowatt hours of the battery bank.

In the example of the Trojan T105 each battery can store 207 amp hours at 6 volts or 1.24 kWh (207 AH X 6 V = 1240 watt hours or 1.24 kWhs). Add a second battery in series and now the equations is 207 amp hours at 12 volts (207 AH X 12 V = 2.48 kWhs) The amperage has not changed but because the voltage is double so it the capacity. Hope that makes sense

[ditto]

Thanks for your post. This is a new coach, delivery in February...noticed a problem first time we dry camped in April. (My wife's idea of roughing it is 30 instead of 50 Amps service).
Tech used a traditional hand held load test meter to test the batteries. All ok.

[nothermark]

FWIW if you have a non contact thermometer to check tire temps you can also use it to check highly loaded connections. Scan each connector while the microwave is on and see if one of them is significantly warmer than the other. A similar technique is to measure across the connection as in from the center post to the crimp lug at a battery connection. The voltage should be very low so any really measurable voltage could be a problem.

[dons2346]

If you are seeing 12.4 volts when the inverter comes back on, you might have the low battery cutoff set to high. Try setting the LBCO to 12.0 or 12.1 volts.

It is all covered in the manual for the Magnum inverter. It tells why you should set the LBCO lower than what you would consider the battery bank 50% discharged state.

[brobox]

Ditto, my coach was delivered with the charging function improperly set to fully charge my batteries. I know QC has improved since my coach was build, but worth checking the charging settings. My batteries showed fully charged, but didn't have a deep enough charge to do much.

[ditto]

This problem occurs after we have been on the road for hours, batteries being charged by alternator, not the magnum charger. Hopefully we will hear from magnum this morning too.

[pasdad1]

Originally Posted by ditto

This problem occurs after we have been on the road for hours, batteries being charged by alternator, not the magnum charger. Hopefully we will hear from magnum this morning too.

......Or NOT ! being charged from alternator.....

If you are plugged into shore power overnight, unplug in the morning and then try the microwave on inverter.....see if it works better then

If so, then you have confirmed batteries not being charged properly by driving

[brobox]

It will be interesting to hear what Magnum has to say. At this point, it sounds like weak batteries not having the amps. I know of one Entegra owner that did have to have new batteries changed just after delivery.

[ditto]

When demonstrating the problem to my tech, we unplugged first, same problem, so two charging sources,same issue. Thanks again!

[photraveller]

Twinboat, I agree the load will be shared by all 8 batteries. I also agree that I over estimated the current draw on each battery (I forgot that we have four groups of 2 batteries in parallel for a moment). I was thinking on my current setup with just 2 parallel groups. Therefore it isn't as drastic for the op's setup.

However, my initial statement of the discharge curve being shorter still stands.

I'll use the T105's that you used: from Trojan's own website:
20hr discharge capacity is: 225AH, 10hr capacity is 207AH, 5hr capacity is 185AH.

If we are discharging the 8 battery bank at 160A, then each battery is discharging at 40A (160 divided by the 4 parallel groups of 2). That is higher than the 5hr discharge rate of 37A.

Using the 5hr discharge numbers, the 8 battery bank capacity is 740AH, while at the 20hr rate, the bank would be 900AH. That's an 18% decrease in capacity.

I realize we are talking 800AH in this thread, but it will still be roughly the same, somewhere in 15-20% reduction in capacity rate from manufacturers rated numbers.

BTW, in a 4 battery setup, each of these T105's drop to ~140AH under the same 160A load (80A per battery). That's a 38% reduction from the manufacturers numbers.

Either way, I just wanted to make sure everyone realized at our higher discharge rates our capacity is less than what the manufacturer claims.