Paralleling battery banks to start engines wont always work!

[vas]

hi,

an observation/question:

24V system (obviously both engines and service)
engine bank 2X180Ah cranking batteries 4yo (flooded)
service bank 4X6V Trojan T105RE, 225Ah deep cycle, 6months old charged daily (well almost) from 600W solar.

Due to "stealing" 12V to start the generator from the earth side 180Ah battery and stupidly not taking note that it gassed or whatever and water level was low, I managed to short a cell in that battery (or something) now registers 21V (as a bank) and 10V or so this one battery.

Typical case you will use the parallel switch/relay to use the juice from the service bank to start the engines, right?

Well, first time two weeks ago with sunshine it did it (with a bit of struggle) port engine seems happier to start, stbrd not so. Port engine has much shorter cables to starter as batteries are just behind port engine. Stbrd engine did start.

Today after 2 days of miserable rainly weather (still heavily overcast and batteries registering as fully charged) tried to start the engines to check some new NMEA2K black box work I did, stbrd just barely cranks, no way to start it. Port started just!


So is it safe to assume that an engine starter bank with a shorted cell, wont necessary crank well enough to start the engines?
Is it due to charge/current you name it "disappearing" due to the higher resistance/whatever you call it of the destroyed battery?

Yes I know solution is a 13mm spanner and shifting the positive from engine to service bank and yes I don't expect this to happen in a decently maintained system.

opinions?

cheers

V.

 

[[2068]]

With both engine batteries connected in series to get 24v, one duff cell will cripple that battery bank.
You'll find that the current that it will be able to deliver will be much lower than a fresh set of batteries due to higher internal resistance, and that the voltage will drop to a very low value when you try to start.

Using the link switch will pull down the voltage of the domestic bank as well, and there will be a large current flow between the banks. The idea of the link switch is that the voltage in a discharged bank will rise as it is connected to a charged bank - it's not going to work well if the voltage on the poorly bank never rises to match, in which case you will effectively be trying to start an engine through the link wiring. Depending on the cabling, this might or might not work, as you have found :ambivalence:

You might also find that a fair bit of heat gets generated in that duff cell - I would replace as soon as possible, it's a situation where a battery can go "bang".

.

 

[Newbroom]

You need to replace the dud batteries immediately preferably in pairs as you will overcharge the other batteries when on mains. There is a serious risk of the dud battery being overcharged till it goes bang.

 

[vas]

yep, my thoughts exactly...

FP, with the parallel link in, voltage will not even reach 24V, and Victron reports 18A draw from service bank (obviously to starter) for 5-10secs then it drops. Still wont work.
Curious and will remove and clean the contacts of the massive thumb thick cable going to the starters on both prt and stbrd engine.

NB, batteries ordered, boat not in use in the marina, just testing. Will be replaced next week, not in a hurry.

Main reason for posting is to alert ppl that a duff battery cell means you may not be able to start with the parallel switch on! Well, you'll have to make a move to the e/r or wherever the batteries are in order to start them up!
Makes one wonder on the use of the parallel switch other than ringing a bell that you need to replace engine starter batteries that is...

cheers

V.

 

[[2068]]

The parallel switch should work to give a somewhat discharged but otherwise healthy battery bank a temporary boost.
But yes, as you say, it’s not a “repair the battery” button

 

[vas]

The parallel switch should work to give a somewhat discharged but otherwise healthy battery bank a temporary boost.
But yes, as you say, it’s not a “repair the battery” button

considering that all the loads are on the service bank and the starter bank only does the engines (so in theory has a v.easy life) the "somewhat discharged but otherwise healthy" bank is imho wishful thinking. Once you have to use the button (and you're lucky to start the engines) you should order new batteries
[unless of course you have windlass or bowthrusters on the engine bank and you've played along while anchored with engines off-I have all such loads on service bank!]

cheers

V.

 

[[2068]]

On my previous boat, one battery was port engine start.
The other two batteries were for starboard engine start and domestic, both in parallel.
The link switch got used a few times ...

 

[Andy Cox]

vas, can I suggest you check the negative terminals and cabling as well, as a poor connection on the engine block or starter motor, depending on whether you have insulated return or not, is just as likely to cause high resistance problems.

Also, it's useful to put a meter across your isolater switch terminals and check to see if you get an increase in resistance whilst cranking, as this would suggest a problem with the isolator which is not uncommon.
Cheers
Andy

 

[halcyon]

considering that all the loads are on the service bank and the starter bank only does the engines (so in theory has a v.easy life) the "somewhat discharged but otherwise healthy" bank is imho wishful thinking. Once you have to use the button (and you're lucky to start the engines) you should order new batteries
[unless of course you have windlass or bowthrusters on the engine bank and you've played along while anchored with engines off-I have all such loads on service bank!]

cheers

V.

You cannot pull 12 volt from half a 2 volt bank, then try and recharge from 24 volt, this will kill one of the pair.

To link start, isolate the low engine bank and only use the domestic bank or starting.

Better to have two start banks, large normal use, small reserve bank or emergency start ( also bow / winch ? ) and domestic. This gives a simple twin vsr charge from both alternators to all batteries, with just a volt / amp monitor for the battery volts and charge amps.

Brian

 

[vas]

On my previous boat, one battery was port engine start.
The other two batteries were for starboard engine start and domestic, both in parallel.
The link switch got used a few times ...

OK, I see, that's a different situation and the parallel switch makes sense!

vas, can I suggest you check the negative terminals and cabling as well, as a poor connection on the engine block or starter motor, depending on whether you have insulated return or not, is just as likely to cause high resistance problems.

Also, it's useful to put a meter across your isolater switch terminals and check to see if you get an increase in resistance whilst cranking, as this would suggest a problem with the isolator which is not uncommon.
Cheers
Andy

Thanks Andy, I'll remove all connectors and check, there are coss (sp?) connectors in there, but some are tired, may have to cut and renew.

You cannot pull 12 volt from half a 2 volt bank, then try and recharge from 24 volt, this will kill one of the pair.

To link start, isolate the low engine bank and only use the domestic bank or starting.

Better to have two start banks, large normal use, small reserve bank or emergency start ( also bow / winch ? ) and domestic. This gives a simple twin vsr charge from both alternators to all batteries, with just a volt / amp monitor for the battery volts and charge amps.

Brian

Brian you're of course correct,

I assume you missed a 4 in the first line, it was a temp solution until I bought a dedicated generator starter battery and I managed to destroy a larger battery instead, nice false economy, you live you learn

The setup that I'll use (btw it's the original and afaik the typical in IT boats) is a v.simple two banks setup:

2X180Ah crank batteries for engine start, there's nothing else running off these!
4X225Ah deep cycle charged from a victron mppt 100/30 and 600W solar
iirc, port engine alternator charges house bank, stbrd charges engine starter bank.

and an isolated I bank 12V
1X55-60Ah battery for the supply to the generator, charged either from an alternator that the yanmar doesn't have or most likely a small victron 220V-12V intelligent charger that I do have. Actually I always thought that this battery is only used for the cranking, but turns out that there's (obviously) the generator dash (on -off, indicators/warnings/etc) that does consume some juice AND the el. stop solenoid that is under power for as long as the engine is running. Cutting the power and diesel supply stops, engine stops.

There's also a 3 bank Victron 24/60 mains charger (ok, only two banks in use obviously), but there's no need to use it.
It's nowadays just a backup. This summer I used it once for an hour or so.
Boat is not on shore power, well there is shore power nearby but no need to plug in.
TBH, solar is doing such a good job that even on the hard I barely bother connecting the shorepower unless I'm about to use a v.heavy tool or if I'm about to do a 3h heavy sanding/el.tooling session...

What you suggest seems a tad complicated for my setup tbh, and I already have 200kg of batteries to drag about, no need to up that

cheers

V.

 

[BartW]

hi vas,
plenty of good comments above,

It would be good if you could top-up all your battery banks with the solar panels,
and or install a battery monitor in each bank, (and use the alarm)
too low discharge is the most common cause for battery damage.

If you had all the same battery's, you could install one or more Victron Cyrix battery combiners
https://www.victronenergy.nl/battery-isolators-and-combiners/cyrix-battery-combiners
but I wouldn't do that if the battery banks have different types of batt's


in my installation I have plenty (26pcs) 12V 105Ah battery's, all the same model, (permanently topped up with shore power)
after every season I test all batts with a battery tester,
in the past, after 3 seasons I had to take out 1 or 2 damaged battery's, but could run another season with 2 batt's less,
curently my batt. installation is perfect in this context, (cabling, alarms, protection,) and hope to do at least 4 season's with the batts.
last year I added battery balancers to the two 24V banks.
https://www.victronenergy.nl/battery-monitors/battery-balancer

 

[vas]

hi vas,
plenty of good comments above,

It would be good if you could top-up all your battery banks with the solar panels,
and or install a battery monitor in each bank, (and use the alarm)
too low discharge is the most common cause for battery damage.

If you had all the same battery's, you could install one or more Victron Cyrix battery combiners
https://www.victronenergy.nl/battery-isolators-and-combiners/cyrix-battery-combiners
but I wouldn't do that if the battery banks have different types of batt's


in my installation I have plenty (26pcs) 12V 105Ah battery's, all the same model, (permanently topped up with shore power)
after every season I test all batts with a battery tester,
in the past, after 3 seasons I had to take out 1 or 2 damaged battery's, but could run another season with 2 batt's less,
curently my batt. installation is perfect in this context, (cabling, alarms, protection,) and hope to do at least 4 season's with the batts.
last year I added battery balancers to the two 24V banks.
https://www.victronenergy.nl/battery-monitors/battery-balancer

Bart it was mainly the fact that I was using one of the 2 12V 180Ah flooded batteries to crank and run the generator that fcked things up...
I wouldn't dare charge with the same mppt both trojans and normal flooded batteries and tbh till the point I started playing with the generator these engine bank batteries were fine, never caused a problem!

cheers

V.

 

[MapisM]

I wouldn't dare charge with the same mppt both trojans and normal flooded batteries

Not sure to understand that, V.
The T105RE are also plain vanilla flooded batteries. Better/heavier than most, but same technology, I reckon.
Afaik, the only important things to avoid are:
1) mixing different batteries in the same bank, and
2) any partial usage within the same bank - i.e. drawing 12V from just two of the four 6V batteries in a 24V bank