Before I start... down an electrical rabbit hole

[KerryK]

Hi, hope you are all having a good festive season and looking forward to a new year of great life on the ocean!


I am just about to start trying to understand the set up of the batteries and chargers on my recently acquired 40 yo Roberts 53. So before I start I thought I would tap into the wisdom of the group.
First off - I am a retired engineer (practical rather than theoretical) so know my way round basic electrics.
I am trying to understand and hopefully simplify the electrical system of the boat.


Basic battery systems 24v

Start bank for Perkins 6.345
2x 12v batteries VRLA 720 CCA, RC 145 Age unknown but were doing well before using shore power to charge.

2 house banks -

1, 2x 12v batteries -unknown type or rating all I know is maintenance free so AGM, Gel, VRLA,? - these seem to be going well.
2, 4X6V AGM 190AH (20 hr) 380 RC, 2 of these are great other 2 not so good - issues here started me down this rabbit hole!
Bow Thruster
4X 6Vspiral wound AGM - in good order


Charging systems
Solar through a Victron MPPT (200w)
Older 100 w system - not sure how this is connected at present
400w silent wind Wind generator through its own system.


BEP Voltage sensing relay connected to House 2 and start bank ( I dont know which is 'first' bank yet but I assume it is correctly wired to keep the start bank charged.





Issue

As the boat is in a marina at present I used shore power through the Woods Neptune battery charger to charge the house and start banks after maybe 2 hours on charge I noticed Hydrogen Sulphide (H2S) - turned the charger off some cells on House bank 2 were noticeably hot to touch.
Since that time it seems that neither House 2 or Start bank are holding anywhere near full charge.

The charger should be able to handle the 3 banks ok as it claims to monitor and charge 3 circuits.

Through a BEP monitor system I can see that both house and Start banks are indeed charging when the charger is on. I am not sure yet how the bow thruster bank is charged.


Questions
From what I understand the Solar and wind generator circuits should be protected so no need to isolate before using 240 V battery charger?


If the 240V charger can handle 3 banks independently, what role does the VSR play when charging this way? could there be a conflict?


Future
I intend to install a super cap bank for engine start and to charge this for a house bank - comments?


Thanks for reading - any helpful comments welcome, I will be back on the boat tomorrow to do some more investigation!

[Jammer]

House 2 bank probably has a shorted cell. In essence you now have a 22v string you're charging to the specs for a 24v string. Shorted cells are a common failure mode.


Hard to say if the start bank has its own problems or is being dragged down by the shorted cell on house 2. It is likely that the output of the charger is current limited because of the shorted cell so that the start bank is never seeing the 28-29 volts it needs to charge properly. On the other hand the road to battery hell is paved with broken VSRs so that may be going on, or the start string may just be shot due to the ravages of time. One of the many ways VSRs fail is with a small series resistance that is hard to test with a DMM but is enough to make charging anemic at best, 0.05 ohms is enough to really screw things up. On the other hand your 3-output charger should work even if the VSR is behaving badly.

My advice is to scrap house 2 and replace it and then reevaluate and see whether there are still problems. If cost is a consideration and the house 2 bank is otherwise newer and in good shape you could replace just the bad battery or batteries. People will tell you otherwise and it's true that usually the economics don't work out if the rest of the bank is iffy. Nuance gets lost in most of these discussions.


I don't usually reply to these sorts of threads but you sound like you know what you're doing. Post up once you know how this turns out.

[Jammer]

Originally Posted by KerryK

Questions
From what I understand the Solar and wind generator circuits should be protected so no need to isolate before using 240 V battery charger?

They should be fine.

If the 240V charger can handle 3 banks independently, what role does the VSR play when charging this way? could there be a conflict?

It will probably close while you are charging which will make no difference.

I intend to install a super cap bank for engine start and to charge this for a house bank - comments?

These are not yet common but I believe they are a sound idea. I will probably do this on my boat at some point. Install the caps someplace where they will stay cool and then they will last longer than the boat. I would include a means to safely drain them for service. My advice is to measure the actual starting current of your engine starter using a clamp-on Hall effect ammeter and then size the cap bank based on ESR and a reasonable output voltage, 11v, 12v, you choose. Add a 100% margin from the typical new ESR to provide a reserve as the caps age since ESR is the first thing that suffers. Then add a margin for cold weather which will increase the current to the starting motor, based on the coldest temperature where you want the motor to start. Digikey etc have cap banks, don't pay the usurious prices charged for application-specific engine starting caps.

[KerryK]

Originally Posted by Jammer

House 2 bank probably has a shorted cell. In essence you now have a 22v string you're charging to the specs for a 24v string. Shorted cells are a common failure mode.

That is my suspicion also, but it is good to get confirmation, it is easy to get stuck in ones head and miss the blindingly obvious sometimes.

Originally Posted by Jammer

Hard to say if the start bank has its own problems or is being dragged down by the shorted cell on house 2. It is likely that the output of the charger is current limited because of the shorted cell so that the start bank is never seeing the 28-29 volts it needs to charge properly.

Thanks I will check the volts going to each bank during charge when next on boat, that will help with O/a picture.
The charger is only a 15 amp model and I am waiting hopefully for a manual from the maker.

Originally Posted by Jammer

My advice is to scrap house 2 and replace it and then reevaluate and see whether there are still problems. If cost is a consideration and the house 2 bank is otherwise newer and in good shape you could replace just the bad battery or batteries. People will tell you otherwise and it's true that usually the economics don't work out if the rest of the bank is iffy. Nuance gets lost in most of these discussions.

With the batteries that are currently there it will be an expensive procedure to replace all, and with each battery at 32kg (70 lbs) changing them will be interesting (access). Then the whole Lithium scenario needs to be considered. Will check the open circuit volts on each cell with all loads disconnected.
Cheers K

[ranger58sb]

Originally Posted by KerryK

1, 2x 12v batteries -unknown type or rating all I know is maintenance free so AGM, Gel, VRLA,? - these seem to be going well.

They might be valve regulated, but around here "maintenance free" (without further qualifiers) seldom means either AGM or gel. Instead, it usually means sealed FLA, mostly intended for automobile starting batteries.

-Chris

[Jammer]

Originally Posted by KerryK

That is my suspicion also, but it is good to get confirmation, it is easy to get stuck in ones head and miss the blindingly obvious sometimes.

The gold standard is to disconnect the battery under test, fully charge it, and apply a solid load (at least C/4) for around 30 seconds, and note the voltage while under test. You should get around 12.7 volts for a 12 volt battery, 6.3 volts for a 6 volt battery, etc.


Typically this will cause the electrolyte to boil in the shorted cell, also, because of the series resistance.



https://www.amazon.com/OTC-3181-Heav...=ATVPDKIKX0DER


The cheap testers aren't very precise but are usually enough to find the problem. With a string of 4 batteries in series you should test all of them. The readings should be the same.

[KerryK]

Originally Posted by Jammer

The gold standard is to disconnect the battery under test, fully charge it, and apply a solid load (at least C/4) for around 30 seconds, and note the voltage while under test. You should get around 12.7 volts for a 12 volt battery, 6.3 volts for a 6 volt battery, etc.

Thanks for the suggestion, but after yesterdays tests, the load tester is not needed at the moment.

Update

I concentrated on Housebank 2, disconnecting each battery (6v) testing and charging each under no load conditions
results 2 batteries had voltage at or below 4v, other 2 had 6.4 and 6.7 v


Charged the low batteries individually (with a small 3.8 amp 6/12v charger)
one bat faulted out and would not charge
other accepted charge but would not reach 'full charge status' on charger
stopped charge overnight

this morning the 2 'bad' bats were showing 0.9 volts, and 2.1v The other two 6.2 and 6.4v


So I will replace the bank - the 2 good batts I may use for the Onan generator start batteries.


During the tests I could hear/feel the VSR operating trying to charge the disconnected bank.


The start batteries I will look at today - they are testing low on volts atm.


I still feel there is a conflict somewhere in the charging system that may be resulting in batteries getting the wrong bulk, absorption, and float voltages.
The question now is replacement batteries


Anyone with experience of lead crystal batteries - they sound good (from manufacturers)


Lithium - but my insurer does not like them!


Cheers K

[KerryK]

Update, and the rabbit hole has opened!


And maybe I should post as a new thread.


So the battery bank is stuffed, and after considering options the size of bank I want to get to, weight, and space available. I Purchased 2 300AH LiFePO4 batteries, the price was similar to replacing the 4 6v AGM anyway.



And with that I looked at the wind solar charger for that bank (already installed) as I will need to reprogram that for LiFePO4 and found it is not working, or has maybe switched off.

The setup is a SilentWind 400+ with a Hydrid controller with a 100w solar panel connected. I have no manual - but have found what I think is the correct manual on line, but the instructions on how to use it are not to me very clear, There is supposed to be an app from Silentwind - but it does not seem to exist


Question 1, Does anyone have experience with this controller and programing it through the single "scan" button? (I have of course tried to contact the maker and local agent - no response as yet)


Second question re LiFePO4's and charging via the alternator: When charging from the alternator (which charges the SLA start bank + another SLA house bank) do I need to connect the LiFePOP4's through a DC to DC charger to protect the alternator? (due to the high charge current of the LiFePO4's). At present with the AGM's that are to be replaced charge from the start batteries via a VSR.
Could I for instance install the DC to DC charger after the VSR?



Thanks Keiron