House power dipping low, causing problems

[haveaday]

I'm having some troubles with the 12v house power on my boat. I believe this is a relatively complex series of interactions going on so it's going to be a bit of a challenge to get to the bottom of it.

Here's what is happening, I think. When running on generator and one of the AC compressors kicks in this seems to momentarily lower the incoming voltage to the inverter. The voltage seems to be dipping low enough to cause the inverter to unlatch from the AC and being inverting power from the house battery bank. Seemingly as a result of the shock load on the house bank the house voltage then dips low enough to cause issues on the 12v side. Occasionally causing an MFD to reboot and issues with the KVH C3 sat dish.

The house bank is composed of 8 GC2 6v batteries wired in 12v series and parallel. The batteries are fully charged, showing 13.4v (float) and seemingly pretty healthy. If I shut down the generator and just run off the inverter once the load is transferred to the inverter everything works just fine. The house bank holds voltage, etc.

I'm not sure where to start. I've checked the batteries, they all seem to be fine, no uneven heat, etc.

Thanks
Ben

[Diesel Bill]

What's the rating on the generator and how much other load while running. Possibly running close to or at max load capability of the generator and it can't pick up the additional load. Just throwing out ideas and not saying that's the problem.

[haveaday]

Originally Posted by Diesel Bill

What's the rating on the generator and how much other load while running. Possibly running close to or at max load capability of the generator and it can't pick up the additional load. Just throwing out ideas and not saying that's the problem.

It's a 23kw generator. It shows about 22amps of load on it right now. That's with the AC not running. AC unit is a 24k btu modulating scroll compressor unit. It does seem to show pretty high startup current. Something on the order of 40-50 amps. Once started it seems to draw very little, looks like about 6-10 amps.

Ben

[transmitterdan]

Did it always act this way or is this a new behavior? If this is a new behavior what has changed? Usually things like this happen because something in the system has changed so it helps to think through what maintenance was done or system changes (new equipment, wiring changes, etc.) has been done recently.

[smac999]

You need to look st the ac voltage and freq at the gen as the ac kicks in. And see how low voltage is going. Or if freq. is drifting

The low cutoff seetings should be adjustable in the inverter / charger.

[Macgregor 26X]

Hi haveaday,

Does your inverter also charge the battery bank?, if so there may be 75A at 12 V being accommodated too? Does the problem occur when the batteries are fully charged, i.e. where they are not taking a charge from the inverter?

[boatbod]

Put a hard start kit on the a/c compressor (or maybe just change it's capacitors) and it will be easier on your genset.

Might be worth testing your house batteries with the inverter shut down too.

[haveaday]

Originally Posted by smac999

You need to look st the ac voltage and freq at the gen as the ac kicks in. And see how low voltage is going. Or if freq. is drifting

The low cutoff seetings should be adjustable in the inverter / charger.

I will do that.

Thanks

[haveaday]

Originally Posted by Macgregor 26X

Hi haveaday,

Does your inverter also charge the battery bank?, if so there may be 75A at 12 V being accommodated too? Does the problem occur when the batteries are fully charged, i.e. where they are not taking a charge from the inverter?

It does also charge the house bank. But, most of the time when this is occurring the bank is already in float. Hence it's taking very small amperage and fully charged.

Thanks
Ben

[jamhass]

First thing I would check are the cables and connections between the generator, batteries, AC and inverter. That would appear to be the common element affecting all.

[Stu Jackson]

Originally Posted by haveaday

Originally Posted by Macgregor 26X
Hi haveaday,

Does your inverter also charge the battery bank?, if so there may be 75A at 12 V being accommodated too? Does the problem occur when the batteries are fully charged, i.e. where they are not taking a charge from the inverter?



It does also charge the house bank. But, most of the time when this is occurring the bank is already in float. Hence it's taking very small amperage and fully charged.

Thanks
Ben

Picky, I know, but inverters don't charge.

Depends on how long it's been in float:

Battery Acceptance by Stu Battery Acceptance

Why Going Into FLOAT is NOT Full

Why Going to Float is NOT Full

[haveaday]

Originally Posted by Stu Jackson

Picky, I know, but inverters don't charge.

Depends on how long it's been in float:

Battery Acceptance by Stu Battery Acceptance

Why Going Into FLOAT is NOT Full

Why Going to Float is NOT Full

I'm not sure I understand the complaint about inverters not charging. The inverter is an inverter/charger. If you're quarreling because it was called an inverter not an inverter/charger.... okay, and you win the award for the most trivial correction I've seen today.


The BMS is also showing the battery as full. The rate of charge acceptance has slid down to a couple of amps and then the inverter/charger goes to float.

[haveaday]

Originally Posted by jamhass

First thing I would check are the cables and connections between the generator, batteries, AC and inverter. That would appear to be the common element affecting all.

I checked tightness around the time I posted this. I found two connections with a very minimal amount of play in them. I torqued them down but haven't been at anchor since I posted to see if that has made any difference.

Thanks
Ben

[haveaday]

This issue continues to be a problem. I've gone through and tested the tightness and cleanliness of all the connections in the strings. This morning I shut down the DC system and broke each string. I then let them sit for a while and I found that four of the GC2s were right around 6.29v and four were right around 6.22v. I'm not sure what would account for the difference in voltage. the four with lower power were the four closest to where the positive connection from the inverter/charger enter the string.

What I think I'm seeing happen is that when a large load hits the generator voltage dips momentarily. This in turn causes the inverter to transfer load from the generator to the inverter. This causes 12v voltage to dip and occasionally causes some of the 12v electronics, mainly MFDs, to reboot. On transfer back from the inverter some of the 120v electronics will sometimes power cycle, things like an LED TV or the DirecTV DVR. I have checked the transfer setting on the inverter. It's set to transfer to inverter at 77vac. With a meter I'm not seeing voltage go anywhere that low, more like 110v from about 121 where generator output normally sits.

I'm wondering if this is an issue with the inverter being too sensitive and transferring load too easily. If it appears there's an issue with the inverter it wouldn't be the end of the world to replace it. It's a modified sine wave inverter and some of my loads don't love the power it produces. On the other hand if it's healthy I'd hate to replace just for the sake of replacing it.

Thanks
Ben

[haveaday]

Another bit of data. Under heavy load the frequency on the generator does seem to slow a bit. Like from 59.5 hz to 58.7 hz or thereabouts. The voltage dips momentarily when a heavy load hits but then returns right to the same 121ish volts it usually produces.