Battery Charging with battery connected -

Been using a Ctek mxs 5.0 for about a year now to keep the battery on my puma topped up, normally once a fortnight when it is not used much. Apart from the first time I used it I disconnect the battery leads before charging. Put it on charge today but this time I have left the battery connected to the vehicle, plenty of info on the interweb to say this is ok. But old habits die hard, 50 or so years of making sure the battery is disconnected from the vehicle before charging niggles at the back of my mind. SO the question I have is - has anybody on here had problems with their vehicles electronics by leaving their smart charger connected to the battery which is still connected to the vehicle?

Wimblowdriver said:

SO the question I have is - has anybody on here had problems with their vehicles electronics by leaving their smart charger connected to the battery which is still connected to the vehicle?

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I do it all the time on all my vehicles, it's fine.

If the vehicle needs an ECU programming (like my Freelander 2 recently), then an auxiliary power supply needs to be connected to the battery, so it doesn't go flat mid programming.

IMO your alternator charges the battery so why should a maintenance charger be any different.

I've charged my FL2 with the battery connected, but in the ECU I found a voltage fault when I connected the reader, cant be sure but I think it's due to the charger which ramps up the voltage slightly to give a forward current.
The defender often gets charged with the battery on but doe6seem to worry too much.
More modern sophisticated electronics may not like it and will cost a fortune to fix.

Same as all the replies above, no worries I do all four of our cars all the time with batteries connected, same at work.

Thanks for the replies lads, puts my mind at ease

The concern is pulse charging. Chargers that use this method give a betterer charge but there is a greater risk to the electronics. Electronics doesn't like it's power rails constantly changing. Some cheap chargers give a nasty spike with the pulse. Vast majority of the time there won't be a problem. You get the occasional car that will have problems because it had a weakness that was going to fail at some point anyway.

Edit: If my chargers are going through a battery regeneration option I disconnect the battery from my FL2. Stops my FL2 using power while it's happening and reduces risk.

I think the problem comes when the battery is very flat and or knackered as it doesn't smooth the input from the charger. I've found a number of the "smart" changers can't cope with e really flat battery and so I have one old no-tech charger that brings them up from dead.

rob1miles said:

I think the problem comes when the battery is very flat and or knackered as it doesn't smooth the input from the charger.

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Good point.
Actually that's the time when a battery does need disconnecting before charging. The cars electronics won't like the voltage slowly increasing, which could result in errors.
If the battery voltage is below 10.5 Volts, it's best to disconnect the battery, until the battery is fully charged.

rob1miles said:

I've found a number of the "smart" changers can't cope with e really flat battery and so I have one old no-tech charger that brings them up from dead.

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This is a common issue with modern electronic chargers, unless they have a repair or de-sulphation function. If the charger does have a de-sulphation function, the battery must also be disconnected from the vehicle, as it will send high voltage pulses into the battery, and anything that the battery is connected to.

I have put a plug on mine so I dont have to open the bonnet, power in or out as needed.

.

Wimblowdriver said:

Been using a Ctek mxs 5.0 for about a year now to keep the battery on my puma topped up, normally once a fortnight when it is not used much. Apart from the first time I used it I disconnect the battery leads before charging. Put it on charge today but this time I have left the battery connected to the vehicle, plenty of info on the interweb to say this is ok. But old habits die hard, 50 or so years of making sure the battery is disconnected from the vehicle before charging niggles at the back of my mind. SO the question I have is - has anybody on here had problems with their vehicles electronics by leaving their smart charger connected to the battery which is still connected to the vehicle?

Click to expand...

I use the same charger and had the same worry and to get round this I isolated the vehicle electrics from the battery with a switch, then wired the charger cable in on the battery only side and I only charge when the kill switch is ‘off’ and the vehicle electrics isolated.

flat said:

I use the same charger and had the same worry and to get round this I isolated the vehicle electrics from the battery with a switch, then wired the charger cable in on the battery only side and I only charge when the kill switch is ‘off’ and the vehicle electrics isolated.

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Ok, out of interest, what “electrics” weren’t isolated when charging your vehicles battery before you installed the switch ?

Nodge68 said:

Good point.
Actually that's the time when a battery does need disconnecting before charging. The cars electronics won't like the voltage slowly increasing, which could result in errors.
If the battery voltage is below 10.5 Volts, it's best to disconnect the battery, until the battery is fully charged.

This is a common issue with modern electronic chargers, unless they have a repair or de-sulphation function. If the charger does have a de-sulphation function, the battery must also be disconnected from the vehicle, as it will send high voltage pulses into the battery, and anything that the battery is connected to.

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Not according to Ctek.

discool said:

Ok, so what “electrics” weren’t isolated when charging your vehicles battery before you installed the switch ?

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Presumably everything connected to the +ve terminal of the battery, that is permanent live when the ignition is off?
I know there isn’t ‘much electrics’ but all the wiring and associated guff is old now, I don’t drive the vehicle more than 2/3 times a month so what’s the harm in disconnecting the battery from the vehicle (what the switch is doing essentially) when parked up or charging.

I have a 5 amp ctek anorl. When i use it i disconnect the battery so my FL2 doesn't nick the charge. Its a bit hungry at times.

discool said:

Not according to Ctek.

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I wasn't necessarily referring to Ctec, as lots of cheaper chargers of similar design also have this function. Regardless of what Ctec say, I still wouldn't want pulses of up to 30 Volts going through my FL2 electrical system.

Nodge68 said:

I wasn't necessarily referring to Ctec, as lots of cheaper chargers of similar design also have this function. Regardless of what Ctec say, I still wouldn't want pulses of up to 30 Volts going through my FL2 electrical system.

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Ok that clears that up
So tell where dose that info on the 30 volts from a 12volt battery charger come from? just so we can avoid that charger which will do that, the electrolyte would be bubbling well before that voltage and there’s no doubt that the battery would also have exploded.
The only dealings with high voltage chargers are with 50volt standby chargers and the batteries they charge.
Of course the Ctek mxs 5.0 charger charges to a max of 14.7volts and at 5amps max. Shown below.

I personally now use a Noco 2 smart charger connected via the power socket in the boot (L322) to trickle charge and maintain the battery

discool said:

So tell where dose that info on the 30 volts from a 12volt battery charger come from? just so we can avoid that charger which will do that, the electrolyte would be bubbling well before that voltage and there’s no doubt that the battery would also have exploded.

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Just information I've picked up over the years.

The desulphation process requires a higher than normal charge voltage, for a good period of time, which is designed to literally boil the sulphate off the plates. My own desulphation charger uses a higher charge voltage of 18 Volts for about 48 hours, which wouldn't be good for the vehicle electrical system.

Some chargers do this with well controlled voltage and current, but some used high voltage spikes to achieve the same result. I've actually seen high voltage desulphations units that pulse 30 Volts into the battery for a few milliseconds. Obviously this kind of desulphation device shouldn't be used with the battery connected, for obvious reasons.

I now know now that with a 12volt battery 15 volts from a charger is over charging and the bubbling wouldn’t be good for the battery, continually charging that is.
Easy to find that out was by removing the caps look-see and checking with a volt meter, oops 16volts, just top up, and it will be fine, but not any more if a sealed battery is fitted, multi meters are cheap and we now have smart chargers that can be left connected for months if required.

With the 50volt systems I dealt, we had 50 single volt very heavy glass cells and bridge in series, hence we now had a 50 volt battery, the floor mounted charger had a commissioning setting and for a later use a variable setting to de-sulphate, something like 58-60 volts was a few years ago and all gone now.
Seeing 50 cells all bubbling away is something to see, AC took care of any fumes most anyway way, battery racks were check every two months, kept my battery service engineer quite for days as the was a few racks to look after in London