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linking a battery to the vehicle battery electrics when changing


silverback

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Hi all, looking for thoughts or advise, the scenario......the last time i topped up the starter battery i undid the electrics to the terminals, topped up then reconnected, then when switched on the airbag light came on and would not go out, so trip to Fiat and the replaced the airbag ECU as a good will gesture, so i am wanting to check levels again (on my Fiat the electric terminals cover the top up plugs) so to try prevent what happened my thoughts were to link another battery to the +/- wires before i undid them, but momentarily would there be 24v going through the vehicle electrics? or it might just have been a coincidence with the ECU, do garages do this? as you can see i am clueless when it comes to electrics *-) *-)

regards

Jonathan

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Hi Jonathan,

 

If you connect another battery across the starter battery then the voltage will still be 12 V so no need to worry.

 

There are purpose designed devices called 'Memory savers' for just this purpose, here is just one...

 

https://www.drapertools.com/product/22277/12V-Socket-Memory-Saver#!manuals

 

with instructions under 'Manuals' if you want to see how to use it.

 

You could use your leisure battery to power the memory saver while you disconnect the starter battery BUT be very careful as this will leave the positive clamp still live even when disconnected. DO NOT short it to the chassis, negative terminal or even the battery hold down!!! Be very careful what tools, spanners, etc you use.

 

Keith.

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thanks Keith, i have a jump starter suaoki u28 pack and it has a 12v/10a output which i have adapted with croc clips and was gonna use that to bridge the terminals eg https://www.ebay.co.uk/itm/Suaoki-U28-2000A-12V-Car-Jump-Starter-Pack-Battery-USB-Power-Bank-LED-Flashlight/223218826188?hash=item33f8e0fbcc:g:7FUAAOSwUUdazHAy:rk:33:pf:0

hope that will do it, i will put my multimeter over it and see what it is outputting

jonathan

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The usual reason for failures after Starter battery maintenance is the battery leads shorting out on the surrounding metal.

 

I would suggest that if you keep these leads 'live' with a supplementary 12v feed you increase the chances of problems.

 

We would advise you don't power them, just take great care when disconnecting the clamps.

Aim for a nice clean, fast break of the Negative clamp, not one where the leads can repeatedly spark on the battery terminal, insulating it before putting it to one side.

 

Then remove the .Positive clamp, also insulating it before continuing.

 

 

Quality OEM Starter batteries (not the budget after market batteries) don't generally lose fluid. If yours need regular topping up then I would suggest you look at the charging system, particularly Solar or mains EHU charging?

 

 

 

 

 

 

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I'm guessing most people with the battery at their feet can only access one or two cells to check on fluid levels without removing the clamps etc. So a question for Allan, how likely is it that the one cell you can check is substantially different from the rest? Would it be possible for all others to be dry while the one is showing a normal fluid level?
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thanks for the replies, the battery is the original from manufacture so at least 7 years old (due to standing around before being built) the last time i did this maybe 2 years ago it needed minimal water (100ml i think) it seems to be working as it should be, just thought i would check it out, also the way it gets used is differant to other motorhomes in that it powers the drop down tv screen and also the piece of rubbish that auto trail call a media pack so the tv is also on that screen at the same time, also if you are on hookup and the charging (by the sergent 500 ) was charging the vehicle the next time you switch the panel on the 12v is run by the vehicle battery and if you don't notice this we can get below 12v on the vehicle battery....well thats what it seems to be doing *-) *-) so just thought it might need some water, hope all that made sense :-D

regards Jonathan

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Jonathan,

 

I carried out a smilar procadure on our Skoda Fabia earlier this year, when changing the battery, and not wishing to risk losing the radio code. If you still wish to proceed, here is the method that I adopted using our lawn tractor battery, and which was designed to minimise the risk.

 

1. Make up a pair of red and black leads about 2m long. I used available 2.5sq mm flexible. One end crocodile clips for battery, other end 6mm ring terminals at vehicle end. (Confirm spare stud size, and that it is connected at battery positive fuses.)

 

2. Use a preinsulated spanner. Preferably a short 10mm one. (I was able to use an insulated nut spinner.)

 

3. Clip red lead only to additional battery positive.

 

4. Using a spare M6 nut, secure the other end of the red lead (6mm? ring terminal) to spare stud at battery positive fuses. (This is perhaps the most hazardous part.) If fuse cover is removed, replace it temporarily.

 

5. Again using a spare M6 nut, connect the black lead to the vehicle battery negative clamp, and then clip onto the additional battery negative. Both batteries are now in parallel. It would be a sensible further precaution to cover the additional battery with a plastic or wooden box etc.

 

6. Disconnect the vehicle battery negative, and ensure that it cannot spring back into contact with the battery terminal.

 

7. Carefully disconnect and remove battery positive fuse box. Insulate in plastic bags (plural).

 

Restoration is a reverse of the above.

 

PLEASE DO TAKE NOTE OF KEITH'S ADVICE EARLIER IN THIS THREAD.

 

Alan

 

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Keith,

 

Please read the closing line of my post again. I fully believe, that as often happens I was agreeing with your post. I considered an inline fuse, but omitted it in the posting in order to keep the method simple. Make something too complicated and it is not adopted, or misunderstood. When carrying out the operation on my Skoda, I fitted a midi fuse to a spare position by drilling out the holes to suit the Skoda M6 studs. There is no similar spare position on Ducato x250........

 

As I said, I agree with your posts, and I do not wish to start an argument. Certainly it would be even safer with a fuse, but you are still handling a the live battery fusebox. You advised of the danger, and I attempted to re-emphasise that section of your post.

 

Alan

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tonyishuk - 2018-11-09 4:37 PM

 

If / when you do this job, Please let us know how you get on and if top up was needed.

 

My battery is about the same age and I have never checked it, although the habitation battery is checked twice a year.

 

Maybe it's time I took a look.

 

Rgds

 

exactly thats why i am doing it , hab batteries checked also 2 times a year, and they take 350 ml every 6 month each battery 8-) they are banners 4 years old but according to other sources they are rubbish! my mate has the varta 90 he says there rubbish! but that is for another thread i will let you know how i get on in doing this in the next few days

Jonathan

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Alanb - 2018-11-09 7:14 PM

 

Jonathan,

 

I carried out a smilar procadure on our Skoda Fabia earlier this year, when changing the battery, and not wishing to risk losing the radio code. If you still wish to proceed, here is the method that I adopted using our lawn tractor battery, and which was designed to minimise the risk.

 

1. Make up a pair of red and black leads about 2m long. I used available 2.5sq mm flexible. One end crocodile clips for battery, other end 6mm ring terminals at vehicle end. (Confirm spare stud size, and that it is connected at battery positive fuses.)

 

2. Use a preinsulated spanner. Preferably a short 10mm one. (I was able to use an insulated nut spinner.)

 

3. Clip red lead only to additional battery positive.

 

4. Using a spare M6 nut, secure the other end of the red lead (6mm? ring terminal) to spare stud at battery positive fuses. (This is perhaps the most hazardous part.) If fuse cover is removed, replace it temporarily.

 

5. Again using a spare M6 nut, connect the black lead to the vehicle battery negative clamp, and then clip onto the additional battery negative. Both batteries are now in parallel. It would be a sensible further precaution to cover the additional battery with a plastic or wooden box etc.

 

6. Disconnect the vehicle battery negative, and ensure that it cannot spring back into contact with the battery terminal.

 

7. Carefully disconnect and remove battery positive fuse box. Insulate in plastic bags (plural).

 

Restoration is a reverse of the above.

 

PLEASE DO TAKE NOTE OF KEITH'S ADVICE EARLIER IN THIS THREAD.

 

Alan

 

thanks Allan that is what i am gonna do, i am electrically nieve but i do know about the terminals and wires touching things , but good advice along with keith . so i will proceed and will let the thread know how i get on.....that is if i am not frazzled with sticking up hair and burnt fingers :-D *-)

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I suspect your engine battery at 7 years old has reached end of useful life and needs to be changed.

 

Provided the motorhome charging circuits are off or disabled it should be straight forward to change the existing battery. If the charging system is active and the battery disconnected it could be that a higher voltage than normal could be injected into the vehicles electrical system.

 

First remove the quick release clamp on the battery negative post, then the fuse assembly from the positive post, all the cables can be left connected to the fuse assembly.

When refitting connect the negative post last.

 

I am sure the advice to connect a second battery whilst disconnecting the engine battery is well meaning but is not necessary and makes the process more prone to accidental shorts, injury and electrical damage.

All procedures in the official workshop manual relating to work on the electrical system state that the battery negative must be disconnected as the first step, hence the quick release clamp on the battery post.

 

Mike

 

 

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Fully agree with the above posts. It is attempts to keep the vehicle electronics powered whilst the battery is disconnected that might cause more problems than simply disconnecting and reconnecting it properly, taking necessary precautions.

 

I would also recommend isolating the solar regulator (if fitted) and leisure batteries before disconnecting the vehicle battery. On my van at least, I found that electrical pulses were still being sent to the vehicle electronics with the vehicle battery disconnected until I also isolated the leisure batteries and solar regulator. Whether this was via the solar regulator function that sends a small current to the vehicle battery, the sensing cables to the battery monitor or elsewhere I didn't bother to try and find out, but isolating everything by disconnecting the solar panels and pulling the main leisure battery fuse solves the issue.

 

I'm not sure about a 2012 Ducato, but on my 2016 van the radio doesn't need to have its code entered on reconnection. It simply communicates with the body computer once the battery is reconnected and confirms that it is still in the right vehicle, which can take up to 20 minutes, but is usually much quicker.

 

I've never found it particularly arduous on any of the vehicles I maintain to enter a radio code and possibly reset a few things like the power windows after reconnecting the battery though!

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I also use a lawnmower battery to keep the data intact, I couple it to the positive clamp and to the car chassis or engine (+ to + and - to -).

When disconnecting the battery I remove the batterys earth strap from the vehicle body then the positive from the battery, the positive clamp is then put into a glove or something to prevent it touching the earth.

Plus to plus and minus to minus will give 12 volts, the only way that 24v will be present is if you couple the leads the wrong way round.

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