Starter battery going flat

[Trilby Tim]

For some reason my starter battery is going flat I have a standard car battery (specced for the VW Polo that the engine came from) as a starter battery and a domestic bank of 6x110Ah sealed leisure batteries. i have a Smart Gauge and Smart Bank set up which parallels them when on charge and separates them when they're not getting charged. I spend most of my time on mains hook up via a Victron Inverter, so <90% of the time the system is on charge in float mode. However when I need to start the engine and I've been disconnected to the mains for some time (so maybe the domestic bank is down to 60% SoC) and the Smart Bank has separated the starter from the domestic bank then I find that the starter battery is flat. Either the engine barely turns over sluggishly or just a click from the solenoid and nothing more. When I use the "Emergency Connect" feature on the Smart Bank to pull in the paralleling relay to effectively jump start from the domestic bank then it starts easily. Luckily so far I've never been in the position of having a flat domestic bank! I thought that maybe the starter battery was just knackered so a few months ago I replaced it (with the heavy duty option for the car), but tonight I disconnected from the mains for a few hours, tried to start the engine and just a click, no turning!

How can the battery get flat when it spends almost it's entire life connected to a charger?! What's going on here? I do believe that my domestic bank is in need of replacement. i got the leisure batteries second hand 5 years ago and they no longer last very well when I do go cruising. So I could do with replacing them when I get round to it, but I don't see what that should have to do with why the starter battery seems to die. After all the domestic bank always has enough power to start the engine (luckily!).

[trackman]

Something has to be using power from the starter battery if you're sure the battery is good.

Could there be some fault like we once had, where the engine heaters were coming on when they shouldn't due to a faulty ignition switch, for example?

If you have or get a clamp on ammeter that can measure DC (not just AC) then you can check where current is flowing in the cables connected to the batter and trace any losses.

Have you tried turning off the starter battery isolator switch & seeing whether this stops the battery going flat? You could try that even if you haven't the ammeter. It won't tell you where the power loss is but might stop it happening.

[Pete & Helen]

Also worth checking the voltage at the battery terminals during charging to see if its getting a good charge or not. But clamp meter worth its weight in

gold when it comes to sorting electric problems out

[Arthur Brown]

Basics, measure current into the battery, voltage at battery and currents going out of the battery. Other than the starter motor! Where are the bilge pumps fed from?

[jonesthenuke]

How old is the starter battery, it may simply gave failed and you are relying on the Smartbank. If you disconnect their starter battery from incoming supplies does it hold charge or drop to a low voltage? Also check SG if you can.

[bottle]

Check and clean all connections appertaining to the start battery and the starter.

 

You may have a high resistance on the connections, that the start alone cannot overcome but the start/ domestics combined can.

 

Check the start battery is indeed being charged.

 

Depending on findings, will influence the next step.

[Tony Brooks]

I see we have no no starter battery voltages so the diagnosis is solely based upon the starter not doing as it should. We need both the open circuit battery voltage and the cranking voltage, then we can start to do the diagnosis. All the advice so far has been good but it could also be (assuming a four brush starter) that the starter brushes have worn so now only one of the pairs is making contact with the commutator. This reduces the motor power by half but with the higher charging voltage that one set of brushes just might be able to spin the engine. There could be other starter faults that cause this as well so we need some measurements to move forward.

 

PS - anyone mentioned a potential faulty starter master switch? Especially if it has a silly plastic key!

Edited February 21, 2015 by Tony Brooks

[David Schweizer]

Which battery do you have? There is more than one size specified for the VW Polo, if it is the smallest 44Ah one, it is probably too small. Even the medium one intended for the 1.6 diesel engine is prety paltry at only 60Ah. The 75Ah should be OK.

 

I have found that aftermarket equivalent batteries rarely match the performance of the official VW issued ones, and have had to replace them in the past because they were not holding their power.

Edited February 21, 2015 by David Schweizer

[Trilby Tim]

The battery is a 60 Ah 520CCA Lion. It was new just over a month ago having replaced a previous one that was behaving the same. I've checked and cleaned all the connections. When it fails to start, the battery voltage goes very low, about 4 or 5 volts, even the digital clock on the dashboard (used the Polo instrument cluster too!) resets itself.

[David Schweizer]

The battery is a 60 Ah 520CCA Lion. It was new just over a month ago having replaced a previous one that was behaving the same. I've checked and cleaned all the connections. When it fails to start, the battery voltage goes very low, about 4 or 5 volts, even the digital clock on the dashboard (used the Polo instrument cluster too!) resets itself.

 

Was the same make of battery?

[bizzard]

It would be wise to go to a 90amp battery as boats aren't like cars which get used frequently. Boats need some battery capacity in reserve to cope with infrequent use, especially on an indirect injection engine with heater plugs.

[Trilby Tim]

David, no previous was a Varta, similar spec though. A bigger battery might help, but not sure it's the answer. It's not a question of being a bit sluggish or slow to start, either it starts easily or it doesn't turn at all.

[Neil Smith]

Are you sure the mains charger is charging the starter battery first and not the house bank as if like you say they are old they might never get to full charge so never switching over to starter battery.

 

Neil.

[Tony Brooks]

That voltage suggests either the battery is flat/faulty or you have one hell of a load on it. You can probably rule out a brush or master switch fault. Also bad connections. Does the starter motor body or the solenoid get hot when the voltage drops like that?

[Higgs]

David, no previous was a Varta, similar spec though. A bigger battery might help, but not sure it's the answer. It's not a question of being a bit sluggish or slow to start, either it starts easily or it doesn't turn at all.

 

 

When this has happened to my starting system, it meant cleaning all the leads in that system. You have to listen as well to the solenoid clicking. It may click once and then refuse the next time. If you haven't already checked the wiring it would be worth doing.

[Trilby Tim]

Neil, that's not how this system works. The Victron is only connected to the domestic bank, but when the SG detects charge going into either the domestic or the starter then it closes a paralleling relay so connects it all together. So in practice my system spends most of the time with all 6 domestic and one starter all paralleled together and all connected to the charger at float voltage.

[Trilby Tim]

It does feel to me that the problem is something to do with the time the starter battery spends paralleled to the domestic bank. Take what happened yesterday and today as an example:

-On Friday at some point while I was out the power on the marina went down so the Victron stopped charging and flipped to Inverter mode. Soon after the SG would have separated the starter from the domestic bank.

-When I got back (no more than 8 hours of not being connected to mains hook up) I tried to start the engine. Completely dead, just a click from the solenoid. Emergency connected the domestic bank via the Smart Gauge and started easily. Ran the engine for just over an hour to charge both banks.

-Went to bed and more than 12 hours later tried to start the engine, this time it started fairly easily only using the starter battery. Ran it for about half an hour this time.

-After another 4 hours or so tried it again and again it started easily just from the starter batt. Mains power from the marina is now back on so it's now charging again through the Victron.

 

So if there's a drain on the starter bank then why does it drain in less than 8 hours on Friday but not in more than 12 hours on Friday night/Saturday? And if it's poor connections then again why no start on Friday but yes on the other days? I can't understand why being left on float seems to the be the problem, but it does appear that way.....

[Alan de Enfield]

It sounds to me that the Victron is at fault.

 

Charge the starter battery via the Victron and its 'flat'

Charge the starter battery via the alternator (engine running) and the battery is charged.

 

You say the Victron switches to inverter mode - could it be drawing all of its supply from the starter battery ?

[Trilby Tim]

The Victron is directly connected to the domestic bank. It's only connected to the starter battery when the Smart Gauge relay is closed. I was using the Victron in Inverter mode during the 12 hour period that was fine. As an experiment I've set the connect threshold voltage up to 14V on the Smart Gauge. So now it only closes the relay when the Victron is charging in bulk or Absorption mode or the engine is running.

[Tony Brooks]

Realised last night that my last reply was by an idiot! Read "instrument panel voltmeter" thought "multimeter on battery". Of course that low panel meter reading could be faulty wiring, connections or masters switch. Lets have the open circuit and cranking voltages at the BATTERY>

Sorry.

[Neil Smith]

Can you disconnect the victron from the start battery and see if it starts then, as we all know you should be able to leave the boat for a long time without charging and it should start with a new fully charged battery.

 

Neil.

[Trilby Tim]

I have checked the voltage at the battery when cranking in the past and it reads the same as the panel. I admit I didn't do it this latest time because I didn't have anyone handy to turn the key while I held the multimeter on. But the Smart Gauge is directly connected to the battery terminals on its own dedicated cabling, there's no isolator switch or any other wiring that the Smart Gauge will read.

Nei: that's basically what I've done now. I've set the SG to keep the batteries separated at float voltage, so I'll leave it for a few days like that and see if it starts.

[Maffi]

I had this problem a few years back. Turned out to be the earth line high resistance causing a large volts drop). To test try connecting the battery negative terminal directly to the engine block with a jump lead if that works then clean up the terminals at each end and if necessary any in the run. I replaced the lead with a decent piece of welding cable. After a long time of problems it was a relief to have the engine start by barely turning the key.

Edited February 22, 2015 by Maffi

[Arthur Brown]

Use an ordinary DC voltmeter to look for volts drop under load along all the circuits connected to the starter battery, any connection will drop a couple of millivolts, a bad connection will drop 500mV or more under starter load. A single steel washer in the current path can be enough.

 

As the battery starts the engine when charged probably the fault is somewhere in the circuit that charges it from the mains.

 

While you have mains, a small charger dedicated to the starter battery is a very good idea. You could allocate a 2 - 10w solar panel to the engine battery too.

 

While a boat battery should perform an engine start after three months rest, most car batteries will be dead after one month as there is usually current drawn by the alarm system and some system computers on board -it's almost usual for a family's second car to need help after the Christmas holiday and that is ten days max. Does using the car instrument console cost you any running current? Especially continuous current?

[Trilby Tim]

Found the problem, it was actually as Maffi suggested, in the negative lead, on the connection to the engine block. Using the emergency connect to close the paralleling relay would have also allowed current to flow through the domestic bank's return (which was connected to the engine block on a separate point). So actually when I thought I was starting off all batteries it was actually starting from the domestic bank only!

The problem was when I fitted the engine I had used the wrong nut on the connection. It was a metric stud but I'd screwed an imperial nut onto it. So it was done up tightly, but was tight because the mis-matched thread was locking, not because it was clamping the terminal tightly! Corrosion had got into the loose joint. The correlation to being on mains charge or engine running was possibly coincidence or possibly the vibration of the running engine actually cleaned up the corroded loose joint and made it easier to start the next time. Long periods on mains charge and the corrosion would build up again.

Changed the imperial nut for a metric one, cleaned up and put grease on the connection and it started easily from the starter battery. So the good news is that the mystery is cleared up, the bad news it that it looks like I scrapped a perfectly good battery.