Work-Around for Inverter Charger when batteries dead?

[Elzaar]

So I went to the boat in the boatyard today only to find when they decided to re-wire the power grid (good), they failed to plug in my smart plug correctly (bad) and my batteries are all dead. Which led me to learn something I still am trying to follow the logic of ...


When I bought the boat I had to replace the inverter charger on it. It was replaced with a Magnum and professionally installed. What I have now discovered may not be news to everyone, but apparently if the batteries are dead the inverter can't pass through the AC voltage from shore power because the Magnum itself requires 12 volt to operate. Which leaves me the option of running an extension cord and hoping I can recharge the batteries with an old fashioned battery charger (and fingers crossed). This makes absolutely no sense to me, but I've confirmed it with with the folks who did the install - and I totally respect their work and knowledge. They did say the newer Victrons don't have this issue, but the Magnums and most others still operate this way.


First question, is there a way to build a bypass switch that would allow the shore power to circumvent the Magnum and go straight to the AC Bus in the panel? This seems like a reasonable solution, but the electrician didn't do it before and didn't suggest it now, so maybe I'm missing something. That would allow the AC system to operate and give the option of at least carrying a separate battery charger to re-charge if you could get to shore power. It would also allow the option of carrying a small 12 volt inverter for charging gosh, I dunno, your cell phone to call for help?



Now my rant. This makes totally no sense to me since it would seem that if the inverter charger shuts down due to low batteries (or simple battery failure), it has effectively shut down the boat's entire electrical system and re-charging capability. If I'm following this correctly, the alternator, solar panels, and whatever other systems are wired in couldn't be used to recharge the batteries, nor could they be used to power essential systems simply by running the motor.



This seems insane to me, but perhaps someone here has a good explanation or better still, a work around?


Thanks as always for your forbearance.

[Scubaseas]

If you have a separate start battery one solution is an emergency connect from start to house battery. Or jumper cables. Either would get enough 12V to the inverter/charger to get going. A jump box (jump starter) or small battery would do the same.

[Elzaar]

Good thought. I wondered if the start battery could be used. Would a basic start battery have enough oomph to raise a 400 amp battery bank up high enough to make the Magnum happy?

[Scubaseas]

Originally Posted by Elzaar

Good thought. I wondered if the start battery could be used. Would a basic start battery have enough oomph to raise a 400 amp battery bank up high enough to make the Magnum happy?

Should be fine.

[pcmm]

Originally Posted by Elzaar

Now my rant. This makes totally no sense to me since it would seem that if the inverter charger shuts down due to low batteries (or simple battery failure), it has effectively shut down the boat's entire electrical system and re-charging capability. If I'm following this correctly, the alternator, solar panels, and whatever other systems are wired in couldn't be used to recharge the batteries, nor could they be used to power essential systems simply by running the motor.



This seems insane to me, but perhaps someone here has a good explanation or better still, a work around?


Thanks as always for your forbearance.

Your "rant" under most cases would be incorrect. If the batteries are dead, solar can still recharge them as its power comes from the PV panels (yes the PV panels can powe the MPPT, been there, done that). Your boats alternator should also be able to charge the house bank. If you can't charge your house bank with this other systems, your setup has been architected VERY, VERY wrong!

having said that simply paralleling the start and house batteries should bring the voltage up high enough to get the Magnum charging.

To your point having the Magnum go down will in now way shut down the vessels ability to charge or shut down its electrical system. Just in this case seems to shut off the AC power and that particular charging source. Staring the engine will get the vessel charging again.

Having said all of that the real question here is WHY did your house bank go that flat?

[TBW]

This seems a good place to jump in with my lack of knowledge.
I have had All of these things happen - batteries dead for no reason anyone can figure out - on and on. I have a trawler with 4 x 8d lifeline house and 2 x 8d lifeline start. The 12v charger breaker got turned off by accident one time and the charger (charles) and inverter (magnum) went down. I have an rv with 6 x battleborn 100 amp hour lithiums. Many strange things here too. (Plugged in to shore power, everything turned off, find batteries below the BMS minimum and shut down. Think it is 12 volts for the Battleborns.
Now to my point:
How do I learn enough to sort this stuff out? I recently spent a year getting my genset working - several fingers in the pie (at about 150 per hour) that had to be figured out and undone.
I know "some" just not enough. And really good electrical help is impossible (almost) to find.
Seeking Knowledge
TW

[Phyrcooler]

Yes… you can install a bypass switch. I used a rotary (Blue Seas I believe) switch allowing me to get shorepower distributed in the event of an inverter/charger failure. I did mine after having repeated failures wherein an error code kept shutting everything down. Mine was a Magnum inverter/charger as well.

I will always have a bypass for an inverter because of my past experiences. Given a choice if doing a new install, I’m also in the small camp of preferring to keep my charger and inverter as separate devices.

Your rant is not misplaced. I showed up to my boat at the marina late at night after a long drive for a 3 day holiday weekend. Only to find batteries dead (small parasitic loads will get you… but that’s a different discussion). Zero 12v power. Zero distributed 120v power. It was a very long cranky ride home.

[Elzaar]

Thanks for all the replies. To some extent this has been a good learning experience and also underscores why I find its nearly always a mistake not to do things myself. No knock on the install, only that if I had done it myself I wouldn't have these gaps in knowing what will do what.

Scuba - thanks for the tip on just using the Starter battery. It solved the immediate problem and was enough to make the Magnum happy. The House bank is re-charging now through the Magnum. Stupid that I would automatically know the House bank can back up my Starter, but didn't really consider before going the other way.

Good to know the MPPT will at least theoretically top up my House bank, but then the million dollar question is why did they let the House bank go dead in the first place? Here in the PNW it may be as simple as just the endless gray but it seems worth investigating further.

Also good to hear the alternator *should* work even with the Mannum down, but that's something I will need to verify. Again, if I had done the install I would probably know, but my brain pretty much has to be invloved in the actual work to have that complete understanding of the system.

For the bypass (which I still like), how was that done? Just a standard battery switch put ahead of everything (panel, inverter, etc) and direct to an AC plug?

As to how it all went dead, well, the basic answer is it is in a boat yard. People disconnect plugs to "borrow" the outlet and forget to reconnect, grids go down, and in this case, some worker failed to negotiate the plug correctly. Im not happy about it, but I also realize things sometimes happen and thats why I like things as foolproof and flexible as possible. *If* it turns out the alternator and PV panels can stll charge with the Magnum down, that alone will make me feel much more comfortable since lack of easy AC is a headache, dead in an anchorage with no recharge options would be a much bigger issue.

The deeper answer to your question as to why the batteries went flat is probably a combination of events. The refrigerator was running and that alone would kill the batteries in about two days with only the two PV panels I have installed in Winter on he hard. The PVs would offset in the Summer here, but definitely not in January. Ive tracked down about every other extraneous load but I know from past experience there is at least a trickle of power being used by various "systems." If anyone has any tips how to kill those Im all over it.


I'll be using the response here to go back and ask some questions and make sure I have a warm fuzzy feeling or can make some changes until I do.

So again, thanks vey much for the replies.

[NorthCoastJoe]

One thing you could do for the future is put in a transfer switch on the incoming AC.

The center leg is input, one leg inverter/charger, the other leg direct to your AC breaker input. With a transfer switch you bypass the inverter charger in a safe manner.

[NorthCoastJoe]

I should have mentioned. Make sure you get an AC transfer switch that is rated for above maximum current (amps ) . I would not use a battery switch it is not designed for AC or the voltage. Most AC switches are rated for 600 volts.

[Elzaar]

Thanks for the information. That sounds like a good basic solution.

[Elzaar]

Just to round this out ... I spoke with the electrician and confirmed that the Magnum is generally separate from the alternator and the PV system. However, he did point out that the regulator that manages the alternator and the MTTPs that manage the PVs both also have minimum voltage requirements that could theoretically be issues on their own, but probably not.


He likewise listed the Starter battery as the most likely option if the issue ever came up.



Finally, he also explained that an AC rotator switch could be put in that would put power directly to the AC Bus, but he also explained it is a bit more complicated than the basic gate I had envisioned should be possible.


Again, thanks for all the replies.


For the poster who asked where to go to learn most of this stuff, the best suggestion of where to start I could give would be Nigel Calder's "Boatowners Mechanical and Electrical Manual."



https://www.amazon.com/Boatowners-Me.../dp/0071790330


There are probably other's, as well, but Calder is generally the first name I hear brought up.

[Scubaseas]

Don't know what kind of batteries you have but if they get run flat, like the fridge was on and ran them below 10V the batteries themselves may be toast. Even "deep cycle" batteries can only handle a few run dead scenarios before suffering loss of capacity.

There are also situations where a dead cell or bad battery will "fool" the voltage regulator and not allow charging or makes the charger think the battery is full when it's actually dead.

You might want to check for parasitic draw also to make sure the batteries are not getting drained. I'd also disconnect and load test each battery either with a carbon pile type or good capacitive discharge type battery tester.

As far as "systems " loads the only thing that should be unswitched and wired directly to the battery is the bilge pumps. Get an amp clamp or wire in an ammeter and start pulling fuses or shutting off switches until you find where the draw is. If you shut off everything you should have pretty much zero draw. On a car it would be limited to the clock and the memory circuit in the radio, which are in the hundredths of an amp.

[Elzaar]

They are Firefly Carbon foam 4 volts stacked together. So far they have been surprisingly resilient, but yeah, I am already checking my options for lithiums if these are toast. Only way to really know is to charge them up and see if they handle a load or crash and burn.

Unfortunately, I have to leave the boat again for a month, so has to wait until I get back to real test them, etc.

I did the drill of shutting off switches and pulling fuses a couple times. It still seems like there is more mystery draw than there should be. My RV has the same issue. Not a huge draw, and probably its the ammeter itself, the various shunts, controllers, etc. It all adds up, but if there is anything anyone has discovered I'm open to it.

[Pizzazz]

I would check the inverter/charger setup first to understand what has been done. Typically, the inverter charger would be connected to the house bank only. It will then charge the house bank and the starter bank, either through a manual switch or through an electronic combiner (could be built in or external).

1) Measure the voltage of your starting battery (confirm they are not dead too). If those are dead, take one of the starting batteries to a shop and try to recover/charge it properly.

2) With one good starting battery (or you can just get another battery or the battery from your car), disconnect all other batteries and attempt to switch on the inverter/charger. If need be operate the combiner switch to make sure it is connected to the good battery.

3) Charge and equalize everything. Then, take an amp meter and make sure that you have the switches/capabilities to completely isolate the starting batteries when you are leaving the boat (i.e. current draw should be 0). It would be nice to be able to isolate the house batteries too but usually you have some small loads (radio memory, etc.) that are inconvenient to isolate. A small solar panel usually takes care of that.