Battery Switch

    For a while I've been thinking that it would be useful to have a battery isolator switch, as it would make working on the car more convenient and it would help minimise the discharge of the batteries when the car is not going to be used for a while.

    So, this weekend I fitted one. Attached is my step-by step guide to how to do it.

    I chose a BEP marine switch, which is very compact and water-proof down to a depth of 2m ;-). It has a detachable red knob and most importantly a continuous rating of 275 amps with cranking capacity around 1200 amps (available on ebay for about GBP20).

    Nice work there :)

    And seems like a good idea as well , I have also experienced drained batteries during long time of storage.

    Now my car even run fine after a powercut as it before replacing distributors , rotors and service of DK's needed a run in time.

    Not sure if there are any good reasons for keeping the car with constant voltage??

    :top:

    Regards
    Terje

    Well, without power, the timed-service indicator will stop counting and you'll need to remember the radio Code. Normally, I always disconnect the batteries, but with a switch it's easier.

    Very nice job! I usually disconnect the bolt attaching the ground wires to the body in the left trunk (boot) area, but this way one would not have to have a socket wrench handy. Thanks for the great write-up.

    BMW 850 CSi
    BMW 8er.org Clubs International (B8CI) Board Representative, USA and North America
    Editor, E31 NEWS International E31 Newsletter

    Zitat von arnie;87348

    Well, without power, the timed-service indicator will stop counting and you'll need to remember the radio Code. Normally, I always disconnect the batteries, but with a switch it's easier.



    Guess there is a battery in the display unit for that purpose?
    But that is most likely in poor condition and don't last long.

    Regards
    Terje

    For the last six mid-Winters I've just left my car hooked up to a decent battery conditioner.
    Never had any problems.
    Other than shorts/fire hazard I'm not sure what the benefit to the batteries is if you disconnect them?

    Don't claim any real knowledge here. The finer points of lead/acid battery charge/discharge electrochemistry appear to be so much more complex than I expected.

    Thank you. I guess I could draw one, but I just scribed around the removable plastic baseplate of the switch. This also gives you a template for the screw holes. Once you have marked and drilled the 4 holes for the switch retaining screws, mount the bracket to the car, using the top right hole of the 4 screw holes (this hole goes through the swicth case and the two brackets), and this will allow you to scribe the position of the second retaining hole for the bracket, on the far right. You need to start with an aluminium plate approx 70mm x 200mm and the width of the narrow part of the bracket is 38 mm.

    That' s a nice job. I' ve been thinking about it for a while. In rainy periods my car is always asleep. Last time after 7 weeks batteries were dead and when I jumped the power alarm started and car didn't start until I disconnect the module and it needs to be reset in service. Anyone has any idea how much more, batteries can hold up with any kind of disconnection? And is it normal to drain both of them in 7 weeks?

    Hello Dennis,

    I'm no expert but I remember reading a post on here regards people using battery conditioners/chargers while their cars were in storage. The general consensus was that you can expect the batteries to discharge in about four to five weeks if not using chargers. It wasn't clear whether or not the batteries were connected or disconnected?
    If you're going to use a charger though, the advice was to get the best which are apparently CTEK's.

    Regards,

    Ivan

    01/1994 E31 840i M60 European LHD automatic, prod code EF61

    Thanks Ivan.

    The thing is my car stays outside which is shared garage so I don't have a chance to connect a charger with the cable. I read about solar chargers but again I use car cover all the time so it is not an option too. If it really takes just 4 or 5 weeks to drain the batteries and if it does not much differ that they are connected or not, I think the best options are to keep spare charged one at home and replace left side one in each 3 or 4 weeks OR use the car more frequent ( at least start for a while each 2 or 3 weeks.)

    Thanks again I got the point :)

    Zitat von dennis320;87384

    Anyone has any idea how much more, batteries can hold up with any kind of disconnection? And is it normal to drain both of them in 7 weeks?



    When the car's electrical systems go to "sleep, usually after about 20 minutes, the drain on the batteries should be around 20 -50 mA, which is negligible. However, aftermarket alarm systems can draw a lot more.

    The car has two batteries of roughly 65 Ah. So, if you consider that you might need at least 50% charge to start the car, and if we assume a continuous 50mA drain, then that gives 65 / 0.050 = 54 days or about 6 weeks.

    The shelf life of modern batteries is about 18 months, so you could leave a fully charged battery in place for that long and expect it to retain at least 90% charge over that time. Hence, a battery disconnect switch is the simplest solution for leaving your car long term.

    Zitat von dennis320;87419

    ....I think the best options are to keep spare charged one at home and replace left side one in each 3 or 4 weeks ...





    Both batteries should always be replaced in pairs and be pretty-much identical. If you do as described, the flat battery will draw charge from the charged one and in the long run the batteries will become mismatched leading to shorter life, as the left one will have had, on average, less usage and better treatment.

    Hello All,

    I today took delivery of my CTEK battery conditioner. While my car is off the road, should I connect this to the battery direct (if so, which one), or to the jump-start terminals in the engine-bay?

    Regards,

    Ivan

    01/1994 E31 840i M60 European LHD automatic, prod code EF61

    I keep mine connected in the boot (on the right hand side, just behind the battery). I run the mains lead under the carpet and keep the plug in the wheel well. When the car is not in use, I run a mains lead into the boot. The charger is always connected to the battery.

    Zitat von IvanT;87914

    While my car is off the road, should I connect this to the battery direct (if so, which one), or to the jump-start terminals in the engine-bay?

    It doesn't matter. But the under-hood terminals have the best/easiest access.


    The leads on the CTEK charger are long enough to run them from the terminals to the nose of the car (corner of the hood). Doing so you can even completely close the hood while charging. For the battery terminals in the trunk you always have to take out the side carpet which is a bit clumsy. That can be avoided by making a permanent install in the trunk using the handy connector (CTEK Comfort Connect) that should have come with the CTEK.

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