Se7enUp Posted February 12, 2010 Share Posted February 12, 2010 I have 2 heavy duty batteries in my 110 They are linked using an X-eng split charge however...... When I moved the batteries from my 90 to the 110, I never got round to wiring the split charge to the ignition. As a work around I wired the relay to the +ve terminal of one of the batteries (as a temporary fix) This was in november. Things being things I forgot about this and have been using the 110 pretty regularly - especially over the recent snowy weather. Last weekend I started the 110 and noticed it seemed to turn over a little bit slow, but didn't think too much about it. Tonight I've just been out to start it and it's totally flat - like really flat - no lights, no anything!. I measured the voltage in the batteries and I've got 2.5v in one and 5.6v in the other!!! My guess is that theres something draining the batteries! But is it possible that having the 2 batteries permanantly connected to each other has caused them to gradually discharge (cycle between each other), and as the voltage has dropped, this process has accelerated? If it is something draining the batteries, does anyone have any tips on how to find out what is causing it? Quote Link to comment Share on other sites More sharing options...
Aragorn Posted February 12, 2010 Share Posted February 12, 2010 Connecting two dissimilar batteries in parallel can cause them to drain each other. The other possibility is that the X-Charge relay sucks a lot of juice when live, and having it powered constantly has been enough to drain the batteries over the 5 days. To find out of somethings draining them, disconnect the earth lead, and install an ammeter betewen the earth lead and the battery negative post. Might be an idea to disconnect the second battery while testing this. If theres doesnt seem to be anything obvious, power up the X-Charge and see what the relay coil is drawing when energised. Quote Link to comment Share on other sites More sharing options...
Se7enUp Posted February 12, 2010 Author Share Posted February 12, 2010 Thanks for the reply. Both batteries are identical. I've got the main battery on charge so will try tracing the problem tomorrow. The more I think about it, it must a problem with something that has suddenly started draining the battery. The batteries have been connected together since the start of November and even through the snow and ice, driving everywhere with headlights on and lots of short journeys, it's always started without a problem. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted February 12, 2010 Share Posted February 12, 2010 I wouldn't be surprised if the relay was drawing an amp or so, even normal car relays can draw a fair bit. Try disconnecting the relay coil and just bolting both battery leads to one terminal of the relay to bridge them together if that's the object of the exercise. That way you prove if it's the relay or something else. Quote Link to comment Share on other sites More sharing options...
GBMUD Posted February 12, 2010 Share Posted February 12, 2010 Things being things I forgot about this and have been using the 110 pretty regularly - especially over the recent snowy weather. All the time you are using the car regularly the battery gets a charge each time. Last weekend I started the 110 and noticed it seemed to turn over a little bit slow, but didn't think too much about it. I am guessing that in the period the car was standing idle, the batteries were drained by things like the split charge relay (which does use some current when engaged, a situation that, when wired according to the instructions, only occurs when the car is running), the radio, the alarm etc.. When you started the car it sounds like the batteries were partly discharged. You further discharged them by starting the car. You do not comment on how long the car was run for or what it was used for, but if it was only used on a short journey or left at idle, especially if the lights, heater, rear window etc. were on, you would not expect the battery to receive much charge if any at all. My old Tdi would use battery power (as opposed to charging the battery) at idle if all the electrical systems were on. Tonight I've just been out to start it and it's totally flat - like really flat - no lights, no anything!.I measured the voltage in the batteries and I've got 2.5v in one and 5.6v in the other!!! My guess is that theres something draining the batteries! But is it possible that having the 2 batteries permanantly connected to each other has caused them to gradually discharge (cycle between each other), and as the voltage has dropped, this process has accelerated? If it is something draining the batteries, does anyone have any tips on how to find out what is causing it? Assuming that I was correct above, and that the batteries were not charged last time you ran the car, I would not be surprised to find the batteries discharged after a further period of standing idle. I remember from somewhere that as the voltage drops the current draw will rise in order to maintain the wattage of a device. I am sure Google will shed some light on the fact of that. I suggest charging the batteries (which though they mat be the same brand and model does not mean that they are electrically identical!), connecting the split charge properly and seeing how you go. Remember that the car needs to be driven for the batteries to be charged properly and that running lots of electrical accessories and systems will mean that the battery charges more slowly. HTH Chris Quote Link to comment Share on other sites More sharing options...
Se7enUp Posted February 12, 2010 Author Share Posted February 12, 2010 Hands up - not wiring up the split charge was stupid I know. It was one of those jobs I kept meaning to do, but other (bigger) jobs took priority and it got pushed to the back of my mind. I'm just really surprised how much the batteries had drained in 5 days of not using the motor. The last time it was started, it did only drive about 100 yards and was started/stopped 3 or 4 times! I guess that tipped it over the edge. I'll charge both batteries, wire up the split charge correctly and check with a meter to see what if anything is drawing from the battery. Then I promise to drive it more! Quote Link to comment Share on other sites More sharing options...
GBMUD Posted February 12, 2010 Share Posted February 12, 2010 I'm just really surprised how much the batteries had drained in 5 days of not using the motor. The last time it was started, it did only drive about 100 yards and was started/stopped 3 or 4 times! I guess that tipped it over the edge. I think I see your problem! I think that the batteries were mostly drained before the 5 days began. As you suggest, give them a good charge with the charger and see how you go. It is pretty bad for batteries to drain them that low, you should get away with it once or twice but do not let it happen regularly. Good luck. Chris Quote Link to comment Share on other sites More sharing options...
LR90 Posted February 12, 2010 Share Posted February 12, 2010 FWIW I had a pair of matched Exides wired in parallel for quite a while. Worked great and gave a hell of a kick when starting the car. However, came out one day to find them like yours flat as a pancake, sub 5V on one and about 2V on the other! They never recovered and I no longer leave my batteries wired in parallel when not being used. Quote Link to comment Share on other sites More sharing options...
Se7enUp Posted February 12, 2010 Author Share Posted February 12, 2010 Fingers crossed! Quote Link to comment Share on other sites More sharing options...
Jon White Posted February 12, 2010 Share Posted February 12, 2010 Mine have been permanently wired in parralel for 5 years and have been since i bought them brand new. Never had any trouble! Jon Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted February 12, 2010 Share Posted February 12, 2010 Â I remember from somewhere that as the voltage drops the current draw will rise in order to maintain the wattage of a device. Â I am sure Google will shed some light on the fact of that. Not sure exactly what you are trying to say here, but according to Ohm's Law, that's pretty unlikely... V = IR Where V is volts, I is current and R is resistance, to re-arrange things, we get: I=V/R Therefore as voltage drops with a constant resistance, current will fall, there's nothing magic that is able to decrease the resistance based on supply voltage unfortunately, that's why your lights dim when your battery is getting flat and not charging. Totally agree with the rest of your post, especially the relay coil, which is probably 200-500mA as an estimate, so you could flatten the batteries in a surprisingly short amount of time. If both batteries were 72Ah, and the relay drawing 500mA you are looking at 288 hours until completely flat, and unable to start the engine well before that, which is about 12 days. Quote Link to comment Share on other sites More sharing options...
Se7enUp Posted February 12, 2010 Author Share Posted February 12, 2010 Well, one of the batteries has been on charge for a few hours now and appears to be holding a charge. Hopefully, the other one will be the same. First job tomorrow is to wire up the split charge properly!!! Quote Link to comment Share on other sites More sharing options...
GBMUD Posted February 13, 2010 Share Posted February 13, 2010 Â Not sure exactly what you are trying to say here, but according to Ohm's Law, that's pretty unlikely... V = IR Where V is volts, I is current and R is resistance, to re-arrange things, we get: I=V/R Therefore as voltage drops with a constant resistance, current will fall, there's nothing magic that is able to decrease the resistance based on supply voltage unfortunately, that's why your lights dim when your battery is getting flat and not charging. Well, I suggested I was uncertain. I am not much of an electrical theory type. Chris Quote Link to comment Share on other sites More sharing options...
SteveG Posted February 13, 2010 Share Posted February 13, 2010 Mine have been permanently wired in parralel for 5 years and have been since i bought them brand new. Never had any trouble! Jon same here for 4+ years Quote Link to comment Share on other sites More sharing options...
TSD Posted February 13, 2010 Share Posted February 13, 2010 Â Therefore as voltage drops with a constant resistance, current will fall, there's nothing magic that is able to decrease the resistance based on supply voltage unfortunately, that's why your lights dim when your battery is getting flat and not charging. There are a few things that can pull that 'magic' trick, but I think GBMUD probably read about something with a 'DC-DC' converter in it's power supply - which supply a constant output voltage, so draw more current as input voltage drops. In cars they are usually limited to mobile phone chargers and the like though. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted February 13, 2010 Share Posted February 13, 2010 There are a few things that can pull that 'magic' trick Of course there are, but not employed in an automotive sense, being an electrical/electronic engineer by training means that whilst many things are possible, it's not always best to explain everything when the question is a simple one Quote Link to comment Share on other sites More sharing options...
KKMobile Posted February 13, 2010 Share Posted February 13, 2010 Mine have been permanently wired in parralel for 5 years and have been since i bought them brand new. Never had any trouble! Jon Mine been wired like this for 2 years now with no problems!! even left for 4 weeks at a time without starting!(in extreme cases) Quote Link to comment Share on other sites More sharing options...
TSD Posted February 13, 2010 Share Posted February 13, 2010 Of course there are, but not employed in an automotive sense, being an electrical/electronic engineer by training means that whilst many things are possible, it's not always best to explain everything when the question is a simple one Duly noted, far better to limit all technical explantions to 'magic'. Quote Link to comment Share on other sites More sharing options...
errol209 Posted February 14, 2010 Share Posted February 14, 2010 "Any sufficiently advanced technology is indistinguishable from magic" - Arthur C. Clarke Quote Link to comment Share on other sites More sharing options...
Se7enUp Posted February 14, 2010 Author Share Posted February 14, 2010 Thanks for all the help and advice After a really productive day yesterday, my split charge relay in now correctly installed. Both batteries seem to have recovered well (although I guess only time will tell for sure) I've checked the current drain (after wiring things up as they should be) and all seems well. Apart from the fact my clutch master cylinder now appears to have taken a dislike to clutch fluid! (but that's another story!) Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.