Odd Charging While Under Way

[Midnightsun]

So we have not plugged into shore power for 11 days and my house bank is taking a beating. dropped it down to about 35% yesterday morning pulled anchor and figured things should charge up nicely on the 4 hour planned trip. All the other batteries start1, start2, Bthruster, Sthruster and genny are all 100% as they are essentially disconnected from the house bank.

That being said, as we started moving along I noticed my USB charger read out at 11.3v?? This is not normal while underway. I went down into the cabin and verified my SOC meter. in a minute or so, it would go from +62 amps which would be normal but then dropped to -45a or so. It kept on doing this for the next 45 minutes until I decided to start up the genny to get the shore power charger kicked on. Well this solved the issue and after about an hour or so I shut down the genny letting the alternator take over which at that point worked as they always did. I should also mention the other batteries were charging fine during the entire weird event floating around 13.9 to 14v while under way.

Another thing, I have dual 135 amp alternators, I would think with a large 435AH depleted house bank I should be charge quite a bit more than 60amps.

What happened? I am certainly at a loss. Only thing I can think of is the isolators do no like a severely low battery? Something is not right and am leaning towards the isolators. Any suggestions before I start discarding good stuff.

Are heading to a Marina today to do laundry and fill water and a much needed over night charge.

[Viper]

Are they stock Volvo alternators? Did you try going through the rpm range to see if the output changed? What rpm were you averaging?

What type of isolator do you have; diode, solenoid, etc.? Battery voltage shouldn't matter with the diode type but if it's really low, it may not activate a solenoid, that would have to be pretty low voltage though. Really depends on the type of isolator you have and how it's hooked up, which bank it's sensing for a charge voltage in some cases, etc.

Wouldn't be a bad idea to check all connections, plugs, plug pins, etc. and ensure everything is clean, tight, free of corrosion.

[bud37]

Could it be just your SOC meter, as well, Isolators can be quite finicky as to their trigger volts/amps as well.....check the specs.

OH.... and how was Georgian bay.....you are back in one piece so I guess there are no rocks with your name on them up there now.....

[km1125]

Clarify this part... "in a minute or so, it would go from +62 amps which would be normal but then dropped to -45a or so. It kept on doing this "

Did you have a 45A load on the house batteries at this time? If not, I'd want to know where that 45A was going.

If you did, then that means your total load on the alternators was 107A, because you were charging the batteries at ~62A and supplying ~45A to the other loads. If that's the case, then I'd also wonder what the voltage drop was on the entire wire circuit from the alternators to the isolator(s) to the house battery. I would guess/bet that you're dropping below the cut-off voltage of the isolator(s) if they are active units.

[Midnightsun]

The battery in question is a dual L16 Rolls setup, they are basically brand new. Not really sure how the isolators are hooked up but must assume they interconnect the four banks being, start/thruster, start/thruster, house bank, generator. The are 2 of them, factory install with no modifications EXCEPT, I do have solar connected directly to the house bank which I tried shutting down but did not affect the up and down weird charging. The isolators are the old fashion diode style FYI.



I doubt it would be that much usage but possibly so as the 2 fridges plus and aux fridge plus an aux freezer but even so that would only be around 15a. It was day time so no lights or inverters or anything else going on.

Was planned for Georgian Bay however my wife elected out of doing locks so happy wife, happy life. Been simply enjoying the amazing islands of the 1000 islands region. Am parked at Confederation Basin Marina, Kingston right now for a couple of days.

[Viper]

Those isolators aren't smart per say, they simply pass current through one way and not the other regardless of conditions, no cut off voltage to worry about, they'll just pass on what the alternator is pushing through save for the inherent voltage drop across diodes in general, if I remember correctly, it's about .7 volts. This voltage drop is needed to allow current to pass through. It's hard to tell for sure from the pic but it looks to me like the two isolators are hooked up for redundancy as there are legs from each unit connected to the other unit. Usually done so all banks still charge should one alternator fail though there are dual alternator units available for that.

[Midnightsun]

I thought there were way too many wires involved so yeah, you are most likely correct as to them being connected for redundancy. I also knew these were the older style diode versions which do have that .7v drop.

I would still like to know what happened with that weird charging thing going on, never saw anything like that before.

In another thread I mentioned I want to go Lifepo4 house bank most likely this fall or early spring before I know exactly what I am doing. Part of the process will most likely be removing those 2 isolators and replacing them with sterling 60a dc to dc chargers as the plan to protect my alternators. https://www.sterling-power-usa.com/Ster ... arger.aspx

I am hoping that connecting one to port and the other to starboard start batteries with both of them connected to the Lifepo4 house bank I will be able to get a 120a charge while under way. Need to talk to Sterling about how exactly this works though and maybe they have a better solution. This would be the ideal setup I have thought of so far. An important part of my conversion is to be able to drop in wet cells in place of the Lifepo4 if things do not work out as planned or in an emergency as these types of batteries are simply not available at the marina in a bind.

[bud37]

When you speak to these people explain what happened and see if they have an explanation......something was switching there IMO, I have no idea what. Do you have ACR's in there somewhere ?

Anyway, I had some discussions with Blue Sea and Victron tech when I was trying to resolve the charging problem with the bow thruster, it was interesting to learn how these isolators actually work, in rush current is one of the criteria and voltage points also affect the correct selection or whether or not they will even work as you think. Their input helped a lot to resolve the issue. Good luck man, sounds like quite the project.

[Midnightsun]

Source of the post When you speak to these people explain what happened and see if they have an explanation......something was switching there IMO, I have no idea what. Do you have ACR's in there somewhere ?

Anyway, I had some discussions with Blue Sea and Victron tech when I was trying to resolve the charging problem with the bow thruster, it was interesting to learn how these isolators actually work, in rush current is one of the criteria and voltage points also affect the correct selection or whether or not they will even work as you think. Their input helped a lot to resolve the issue. Good luck man, sounds like quite the project.

I agree 100%, something going on/off at a pretty fixed interval was my observation. Only way I could correct it was to start the shore power charger using the genny and after some charging, things were back to normal. Still trying to figure out what could draw over 60A? I have no big inverter, only a small 400w unit and nothing else capable of high draw except for refrigeration. Have been plugged into shore power for close to 24hrs now and according to the SOC monitor, things are looking great.

[km1125]

You need to map out what you have there. You have four banks (start/thruster1, start/thruster2, house, gen) but yet both the isolators have only three outputs each. It's possible that each directly charges it's own battery and then the three outputs would go to "other engine' start/thruster, house, gen" OR perhaps the gen battery is not part of this configuration. You'd also want to know if there's a sense wire on there somewhere. This would adjust the alternator output to compensate for that 0.7V loss going through the isolator. If this is NOT there, then that voltage drop will definitely affect the maximum draw you'd ever achieve from the alternators.

When charging batteries, it's not the actual voltage (12.8 to 14.2 or whatever) that gets the charging done... it's the DIFFERENCE between the charging voltage and the depleted battery voltage. A battery that only has 25% capacity left still has a resting voltage of around 12.0VDC. When the charging system is active, say at 13.8VDC, then it's the 1.8V DIFFERENCE that's making current flow from the alternator to the battery. You have to add in the internal resistance of the battery and any resistance in the circuit that further limits the max amps that are flowing. NOW, take that alternator voltage and drop it by 0.7V and you've almost cut the charging capacity of the system IN HALF (dropping from 1.8V difference to only a 1.1V difference).

The DC-DC chargers are definitely a cool creature, as they can 'max out' a source while providing all the voltage and current necessary for a load.

I'm still wondering where that 45A load was going. If it was just those fridges, I would think maybe 20A max. Could there be something else running intermittently (vacuflush? macerator?)