Swap starter battery with engine running?

Cavs

Cavs

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Since Sept 2003
Good day. Can any knowledgeable person give a view about whether it's advisable to change the starter battery while the engine is running, please? An RAC patrol did this to my 2017 Ducato and a few days later I noticed the starter and habitation batteries were showing around 16 volts, so I wonder if there's a connection.

Thanks for any advice.
 
It’s not great practice, but, as the engine and leisure batteries are in parallel when the engine is running (unless you have a Battery to Battery charger or similar) no real harm should occur

Separating the leads on the terminal block on a 17 plate Ducato wouldn’t be A good idea either
 
Whatever caused it, 16V from the alternator to any battery indicates that the alternator regulator is faulty. Needs fixing before you need even more new batteries.

It could possibly have been caused by a careless slip as the batteries were changed, but more likely it was like that before, and maybe was the reason for changing the starter battery in the first place.
 
You should never disconnect the battery with engine running , when it was just dynamo and magneto basic electrics not so critical , but with alternator , and so many components that can be damaged by voltage spikes or transients in modern cars , its like playing russian roulette . "are you feeling lucky "

eddievanbitz you need to be very certain ! But that also raises possible other risks
 
tacr2man said:
You should never disconnect the battery with engine running , when it was just dynamo and magneto basic electrics not so critical
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LOL We had to then to repolarise Positive earth vehicles. Those were the days working for the Longlife Tyre and Battery Company
tacr2man said:
but with alternator , and so many components that can be damaged by voltage spikes or transients in modern cars , its like playing russian roulette . "are you feeling lucky "
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I agree, which is why I said its not good practice.

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Probably a daft question ... but why would anyone want to change battery with the engine running?

It would certainly never cross my mind to do this but assume there must be a reason.
 
Thanks for all the replies.

autorouter said:
Whatever caused it, 16V from the alternator to any battery indicates that the alternator regulator is faulty. Needs fixing before you need even more new batteries.
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The c. 16v readings were with the vehicle having been stationary for a couple of days, with the batteries being charged by solar and mains hookup. The alternator seems to be performing properly so I'm trying to isolate the fault on the mains or solar chargers. Vanbitz is being very helpful.

icantremember said:
Probably a daft question ... but why would anyone want to change battery with the engine running?
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To cut a long story short: The vehicle wouldn't start so Fiat Camper Assist sent out the RAC. The patrol agreed with my diagnosis of a duff starter battery and went off to get a new one, which performed no better. He then started the vehicle from a free-standing (smaller) battery from his van and when it was running he took out the small one and re-installed the "new" one, saying that it would charge up while driving. I then drove it for five hours but after a 15-minute stop it wouldn't start again, so the "new" battery was obviously defective.

As a result of this patrol failing to do the job right in the first place, the RAC had to attend twice more. Fortunately, I'm not paying for this (so far).
 
Cavs said:
Thanks for all the replies.



The c. 16v readings were with the vehicle having been stationary for a couple of days, with the batteries being charged by solar and mains hookup. The alternator seems to be performing properly so I'm trying to isolate the fault on the mains or solar chargers. Vanbitz is being very helpful.



To cut a long story short: The vehicle wouldn't start so Fiat Camper Assist sent out the RAC. The patrol agreed with my diagnosis of a duff starter battery and went off to get a new one, which performed no better. He then started the vehicle from a free-standing (smaller) battery from his van and when it was running he took out the small one and re-installed the "new" one, saying that it would charge up while driving. I then drove it for five hours but after a 15-minute stop it wouldn't start again, so the "new" battery was obviously defective.

As a result of this patrol failing to do the job right in the first place, the RAC had to attend twice more. Fortunately, I'm not paying for this (so far).
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Dunno if it's just me, but it doesn't sound like a battery problem.
 
Update: there was a connection with what the RAC did:

I took the van back to Van Bitz where guru Nick used software to interrogate the solar controllers for activity over the last 30 days (Victron controllers, I didn't know it was possible to do this and I don't know whether others have the same facility). Both controllers showed a voltage spike on the day the battery was swapped with the engine running, and one of them then switched into 24v mode, causing the excess voltage I saw a couple of days later. With the bright sunshine experienced over those days (even in the Lake District!!) this caused the nominal 12v system to run at too high a voltage, causing the anomalies including damage to the television, DVD player and head-up display.

Pulling the fuses on the solar controllers the replacing them when I got home reset them to 12v and everything (apart from the damaged stuff) is now working properly.

Thanks for all the replies and thanks especially to Nick and everyone at Van Bitz for high-class, excellent service.
 
Thinking ahead to the day when a cab battery change is required, would a more sensible process be to connect a 12v source (could be jump leads to a non-running car) to the under bonnet lugs to maintain a level of voltage on the vehicle while doing the swap? I’m sure I’ve read on here that some people have had issues with the cab side of stuff after doing a straight swap with nothing connected.
 
Cavs said:
Both controllers showed a voltage spike on the day the battery was swapped with the engine running, and one of them then switched into 24v mode,
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A lesson to take from this is, if you see a voltage of 15 volts or more on the 12V system, you have a problem that needs dealing with promptly, to avoid damage to battery or electrical devices.

Could be faulty alternator regulator, faulty mains charger regulator, or faulty solar controller regulator. Or as in this case, a solar regulator that flipped into 24V mode because of a voltage spike.

Voltage spikes can happen for several reasons. Disconnecting a starter battery while the engine is running is only one of the possibilities. Pickup from nearby lightning during a thunderstorm is another.
 
That was a dumb decision by the RAC guy to swap batteries while running and I think I would have taken me quite a while to trace the errant setting in the victron as a unintended consequence of that battery swap.
Easy when you have the data in front of you though so great work eddievanbitz.
I would probably have been blaming the diode pack on the alternator as thats usually the first thing that fries if you try that trick with the engine running.
 
A capacitor across the solar charger battery output will reduce the chances of it happening again. Cars do get high voltage spikes from time to time, all the other vehicle electronics will have protection.

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sounds like there may be a possible claim off the RAC for damage caused to equipment due to negligence
 
Richard and Ann said:
A capacitor across the solar charger battery output will reduce the chances of it happening again. Cars do get high voltage spikes from time to time, all the other vehicle electronics will have protection.
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That sounds like a great idea... across the battery (the charge line) output
What value capacitor? ordinary or electrolytic?
 
TheBig1 said:
sounds like there may be a possible claim off the RAC for damage caused to equipment due to negligence
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I would bloody hope so, especially with the data to back that claim up!
 
Camping Gaza said:
That sounds like a great idea... across the battery (the charge line) output
What value capacitor? ordinary or electrolytic?
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Electrolytic. Don't know what the ideal value is, I use 10uf on my circuits but I'd go with a bigger one on the controller output, maybe 1000uf?
 
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Or a 16v Zener diode? I've used these before in series with a 10ohm resistor.
 
TheBig1 said:
sounds like there may be a possible claim off the RAC for damage caused to equipment due to negligence
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I agree, but I propose to let my dealer deal with that while I claim under warranty as the RAC was assigned by Fiat Camper Assist.
 
Richard and Ann said:
Electrolytic. Don't know what the ideal value is, I use 10uf on my circuits but I'd go with a bigger one on the controller output, maybe 1000uf?
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Electrolytics need to be connected the right way round in terms of positive and negative. Get it wrong and they swell up and eventually explode with a mess of smelly sticky goo.
 
autorouter said:
Electrolytics need to be connected the right way round in terms of positive and negative. Get it wrong and they swell up and eventually explode with a mess of smelly sticky goo.
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Yeah I know ??
 

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