Advice re battery powered compressor

[Third Golf]

Hi all,

I have a 2017 MkVII TSI.

Do I run any risks of damaging the battery or electronics by connecting a 12v compressor via jumper-lead type terminal clamps to inflate a tyre? Am I better off using the body earth connection point for the negative lead?
Specs. panel on compressor states maximum current draw at 24 amps.
Anxious to avoid any damage.

[gregozedobe]

The only real danger is you might flatten the battery if it isn't at 100% charge when you start (and recent Golfs often are not).

If I was doing it I'd connect to the -ve terminal on the battery first, then the +ve terminal, when I'm finished disconnect the +ve lead first, then the -ve.

[Guest001]

Turn the engine on while using it is the obvious thing to do. And yes you should use the body earth point

[Third Golf]

Thanks gregozedobe and Hillbilly,
Slightly different advice in method; but most importantly giving the nod to proceed, which was the most important element of my question.
I've taken it all in,
Much appreciated.

[gregozedobe]

Turn the engine on while using it is the obvious thing to do. And yes you should use the body earth point

If your car has Auto stop/start Hillbilly is correct, connect -ve to the terminal on the firewall, that way the Battery Management System knows how much charge has been taken out. If not running the engine (to keep battery charge up) then consider using a charger to replace the charge used by the compressor.

[Third Golf]

I do have auto stop/start.
So procedure would be:
1. engine running
2. -ve to firewall terminal
3. +ve to battery +ve, then use compressor.
4. disconnect in reverse
Thanks! Very straightforward.

[minke]

The only real danger is you might flatten the battery if it isn't at 100% charge when you start (and recent Golfs often are not).

If I was doing it I'd connect to the -ve terminal on the battery first, then the +ve terminal, when I'm finished disconnect the +ve lead first, then the -ve.

Hi - can you expand on 'recent Golfs often are not' ? What do you mean by that? I only ask as I've a 2020 GTi and the other week a fellow walking past as I was getting in was telling me he's been through four batteries in 3 years and wondered if I had issues or not.

[Guest001]

Hi - can you expand on 'recent Golfs often are not' ? What do you mean by that? I only ask as I've a 2020 GTi and the other week a fellow walking past as I was getting in was telling me he's been through four batteries in 3 years and wondered if I had issues or not.

Sounds like he has a problem and Have never heard of them going through them like that. Is he talking about Golfs though?????.

Ive done 2 tyres without turning the engine on and its still started . Only put a few Lb in each one though

[minke]

Sounds like he has a problem and Have never heard of them going through them like that. Is he talking about Golfs though?????.

Ive done 2 tyres without turning the engine on and its still started . Only put a few Lb in each one though

Yep Golf. Pointed at my car and said Golf Mark 7 (non GTi). Advised him to ensure that all car keys are well away from the car was the best I could advise

[gregozedobe]

Hi - can you expand on 'recent Golfs often are not' ? What do you mean by that? I only ask as I've a 2020 GTi and the other week a fellow walking past as I was getting in was telling me he's been through four batteries in 3 years and wondered if I had issues or not.

Sure.

Batteries on Golf Mk7 and Mk7.5 cars are often not fully charged and consequently fail more frequently than previous model Golfs. There are two main reasons:

1 VW are fitting cheap, lower capacity batteries (EFB) to many petrol Golfs. These don't last as well under modern high demand usage conditions as the higher quality, larger capacity (and more expensive) AGM alternative. Previous Golfs didn't put as much demand on their batteries so the cheaper batteries lasted well.

2 In an effort to minimise "official" fuel consumption figures VW chose to fit a complex Battery Management System (BMS) to Golfs that have Auto stop/start. This is designed to charge up the battery when the car is decelerating (using "free" energy).

To allow that to happen the BMS doesn't fully charge the battery when driving under power so that the battery has capacity to absorb more charge when decelerating. The end result is the battery is often not fully charged. Batteries last longer if kept fully charged, but because Golf batteries are not kept fully charged they don't last as long. The result is cars with batteries that don't last as long as previous models.

Another minor factor is the BMS should be told (coded) when a new battery is fitted so the BMS can adjust the charging regime to be optimum for the new battery. If not coded the BMS will charge the new battery incorrectly and it won't last as long as it could (the car will appear to operate normally, and there will not be any error messages).

A cynical person (like me) might suspect that VW and their dealers benefit financially from replacing batteries that have failed prematurely, and while they also gain a benefit from the tiny theoretical improvement in fuel consumption, they do not have to account for the extra cost to the environment of producing more batteries than would otherwise be needed.

So what can a Golf owner do ?

I run with Auto stop/start switched off, which suits most (not all) people, but the main solution is to keep an eye on your battery charge, and if it gets a bit low top up your battery charge with a good quality trickle charger at frequent intervals (I use a CTEK). I also carry a jump starter battery in my boot in case I get caught out sometime (can't push start a DSG Golf).

When my current EFB battery can no longer be relied upon (it's still going strong after 4 years) I will be replacing it with an AGM battery (probably Varta or Bosch), and coding the BMS for the new battery.

I hope that explanation helps you understand what is going on.

[gregozedobe]

I do have auto stop/start.
So procedure would be:
1. engine running
2. -ve to firewall terminal
3. +ve to battery +ve, then use compressor.
4. disconnect in reverse
Thanks! Very straightforward.

That looks OK, but I'd add in
1.5 Switch Auto stop/start off (to ensure it doesn't stop the engine while you are using the compressor)

[gregozedobe]

Sounds like he has a problem and Have never heard of them going through them like that.

Either he is letting the car sit for so long without driving the battery is going completely flat (that damages a battery every time it happens), or there is a serious problem with the charging system on his car (unless he is fitting really crappy, under=capacity batteries).

[Third Golf]

Thanks gregozedobe,

For the additional point to add to my compressor procedure list.
And also for the comprehensive tutorial on batteries and the car's charging system management; I've learnt more than what I set out to achieve.

Much appreciated!

[minke]

Either he is letting the car sit for so long without driving the battery is going completely flat (that damages a battery every time it happens), or there is a serious problem with the charging system on his car (unless he is fitting really crappy, under=capacity batteries).

The guy wasn't a "car guy" but serviced at FIve Dock VW (now Leichhardt VW) and said they cannot work it out.

It was just something I kept in the back of my head and it bubbled back up when i read this thread"