Ā My 2004 Mk 2.5 MX5 suffers from a battery drain problem. Please can anyone suggest what I should do next to diagnose the cause.Ā So far I have established:
a) the ādarkā current with everything switched off (courtesy lamps, number plate lamps) is 0.15A.Ā This sounds small but is enough to fully drain the battery if the car is left standing for 2 weeks.
b) there is no problem with the battery - it is new and fully charged.
c) if I remove the āRoomā fuse the ādarkā current drops to zero.
d) I have disconnected the radio and this makes no difference to the ādarkā current.
My questions are:
is this level of ādarkā current normal for an MX5 Mk 2.5?
is it normal for the battery to be flat after standing for 2 weeks?
what should I investigate next to find the cause of the 0.15A ādarkā current? And how?Ā Please note that the car has done a low mileage (18k)Ā and there are no aftermarket accessories fitted.
if I disconnect and reconnect the battery earth terminal I can hear the distinct click of a relay on the left hand side behind the rear seats / at the front of the boot.Ā Does anyone know what this may be?Ā None of the manuals make any reference to a relay in this area.Ā I am wondering whether this could be the cause of the drain.
Ā It drains when stood still - ie no daily use.Ā I have to keep putting it on a battery charger every two weeks to get the car started again.Ā [The car is garaged over the winter - summer/dry use only.]
When it is stood still for two weeks I do not activate the central locking or alarm as I initially suspected it as the cause.
Yes - itās normal Iām afraid. Mine has stood twice (sornād) for up to three months this last two years -Ā battery not dead flat, but down to about 6 or 7 volts in two weeks - But - I leave the alarm and immobiliser on, a) because the car is on the drive, and b) because my insurance wonāt cover it (for anything) if I leave the alarm off. Both alarm and immobilise come on together, when you lock the car with the remote fob.Ā The first time, a mate lent me a trickle charger, so fortunately, as we have a supply in the garage, I left it on trickle which overcame the problem. Since then, Iāve bought my own charger, just in case. The cable from the charger needs to be long enough to reach from the charger (preferably located in the garage, or the house if itās close enough, though that presents problems as to where you feed the cable outside, without running it through an open window) and you can close the boot lid by running the cable to the right of the boot light, where the rubber surround will cushion it, and stop the lid trapping the cable. This means you can set the alarm, and the immobiliser - insurance complied with. - Halfords have a good selection, as usual - you get what you pay for.
Sorry, without a thorough search I canāt tell you what that relay is, but any relay operating will draw some current, and donāt forget the PCM and various items are powered from the battery, granted some are operated by relays which do not work till the ignition is on, however āDark currentā appears to be increased on most NBās. Also - make a note, most batteries have internal āDark Currentā so without any load, or charge,Ā the battery will eventually discharge itself.Ā This is down to internal resistance within the battery.
I would suggest you check your insurance as I believe this applies to cars in a Garage, on the drive and definitely on the street! It is of course, difficult if you havenāt got electric nearby, and cars on the street will get problems anyway, without being prosecuted for obstruction, when some old dear falls over the cable. - Thatās a No No!
Ā Problem first appeared with OE gel battery so I replaced it with a new Westco gel battery supplied by MX5 Parts.Ā No change.Ā I am using an Optimate 4 charger supplied by MX5 Parts specifically for charging MX5 gel battery.
When stood still for two weeks I do not kick the engine over - the drain on the battery would be huge and if I did this I suspect the battery would only stay charged for a week.
I can see a few ways of living with the problem eg. disconnect the battery, take out the āroomā fuse, or leave it on trickle charge all the time.Ā If this is normal for an MX5 and mine is not faulty then I suppose I will have to live with it.Ā But I would really prefer to understand the cause of the continuous 0.15A drain and eliminate it if possibleā¦
I canāt believe it is a normal characteristic - otherwise everyone who parks their car at an airport for two weeks would come back to a flat battery and there would be far more posts about the problem on the internet.
I am aware that the MX5 battery is not very large and not as high capacity as other cars, but even so, two weeks is not that long.
Ā The Mazda manual states the maximum dark current is 20 milliamps, i.e. 0.020 amps. so your drain is far too high.Ā The drain on my car is 0.016amps so that gives a good indication.Ā Ā The relay you refer to is on the passenger side of the boot at the front.Ā If you remove the boot trim you will see it behind the fuel pipes.Ā The function is to control the number plate lightsĀ to beĀ also be used as a boot light.Ā It prevents feed back to the sidelights when the boot is opened and the number plate lights are acting as a boot light.Ā Ā I disconnected mine a long time ago as I found it a nuisance.Ā The connector is just to the passenger side of the boot latch behind the trim.
Ā I measured the ādarkā current with the boot lid closed and it is down at below 0.020 amps, so your suggestion about the relay appears to be correct. (I fed theĀ wires to the meterĀ across the boot seal and shut the lid down onto them.Ā So this resolves the issue of what the dark current really is.Ā But it makes the fact that the battery is going flat within two weeks even more of a mystery.Ā I would not expect 0.020 amps to flatten a battery in two weeks.Ā The boot lid is always kept closed, so the mystery relay canāt be the cause of the problem.Ā Which brings me back to one of my original questions: is a life of 2 weeks normal for an MX5 with a gel battery, if the car is not driven or started up in that time?
Leave the smart charger connected while not in use, that is also what it is for, and kick her over once a week please, use the windows a couple of times up and down, switch the lights on for a couple of mins, flash the indicators, turn the heater on,and if it does have A/C switch that on for five mins or so, to keep everything going.
The Westco battery (according to MX5parts) has a capacity ofĀ 31 Ah
A drain current of 20mA for a day is 0.5 Ah.Ā So at that rate it should last for about 60 days.
The question is whether your battery is fully charged to start with?Ā If you have a digital multimeter can you measure the voltage as the battery is being trickle charged for several days, then switch off charger and continue to note voltage until it stabilises. You should expect 13.4 to 13.6 Volts on float charge and up 12.9 Volts fully charged (off charge). A battery is considered discharged when the voltage is 11.7 V. The state of charged can be judged from the voltage between these limits.Ā Roughly 10% charge for every 0.1 Volt above 11.7 V
I would still be interested to hear if anyone finds they can park up their MX5 for several weeks without trickle charging it, or running it, and not experiencing any problems.Ā I would reasonably expect perhaps 4-6 weeks rather than the 2 I am getting.
Ā Hi, Yes I was thinking along the same lines as RB.
Our car stands for weeks without a problem and so have several hobby cars weāve had previously. I never use a floatĀ chargerĀ but do keep an eye on battery voltage with a digital voltmeter, which can tell the state of charge, and give it aĀ charge every month or two if needed during longer lay ups. Batteries donāt like to be deep cycled so recharge ifĀ itĀ drops toĀ 12.2V.
Your batteryĀ may beĀ in a low state of charge or may have reduced capacity. Give it what should be a full charge, remove the surface charge, then check the voltage. You can also check the alternator for charging with the meter looking for 13V - 14V range running at 2000rpm to see if that is causing a low battery.
Hereās the chart I use. Itās important that you firstĀ remove any surface charge from charging or running by putting on the headlights for 2 mins before taking the voltage, then switching off and taking the voltage, or leave it standing after charging for several hours,
Thereās a basic flaw in your argument, as the voltage drops, the current drawn increases (Ohms law) you canāt draw .020 a for 60 days without having a totally flat battery before you get there, the volts will drop and the current increases. The resistance (the dark current has to overcome this) remains static, but the effect is indisputable. Not going to argue about the daily draw (though itās .48 amp on day one) but this will gradually increase as the voltage drops. If you donāt believe me, connect a flashlight bulb to a new 1.5v battery, and monitor it over a few days, with a meter permanently in circuit. Use a high resistance meter btw, or it will also drain the battery quicker! 10Kohms per volt, or better. TBH - I canāt be bothered to get the text book out - even if I knew where it was - Iāve lived without it for 50 odd years, itās like the law of gravity, it doesnāt change, so I canāt give an accurate voltage drop/current increase cycle time, but I know it happens. 1) I looked after a huge battery rack for several years, and when I did my National Service training course (RAF Tech School - Melksham) I majored in battery technology - proof enough?
Ā Hi I was really interested to read this thread; I got my MX5 1.8 six days ago and on the second day had a flat battery; I havent a clue about anything mechanical, Iām used to my car just starting when I turn the key.Ā Iām now really nervous in case I get another flat battery - I work shifts about 25 miles from home, so dont really want to be stranded when I finish work.Ā Iāve bought some jump leads which will hopefully be useful if anyone is around as I finish work if thereās a problem.
What I really need to know though is how can I get this properly sorted out?Ā I darent even play the cd player at the moment
Well thats also one of the ājoysā of getting a new car. Iād take your car to one of those tyre and battery sellers. They will usually be able to check the condition of the battery for you and the better ones might be able to tell you if the alternator is charging it.
The problem they are talking about above is a car thats not used for weeks. A car thats used daily will usually keep the battery charged up in excess to any requirements by playing the stereo or using the lights for your 25 mile commute.
Gerry ā¦ Never thought iād hear, or wanted to hear those two dreaded words againā¦ Ohms Lawā¦ shivers We had that drummed into us at college, as well as many other just as interesting electrical principals.
The chart you are using is for open lead acid cells. The voltages for AGM cells (or any cells with calcium added ) is about 1.5-2.0% higher. at the top end. The bottom end is fairly arbitary.Ā The so called āreserve capacityā of a battery allows discharge down to 10.5 volts.Ā AdoptingĀ 11.7 V as discharged is very conservative and means that the battery is still fully capable of itās starting duty.
Gerryn
If the resistance is constant then the current (I) falls as the voltage (V) falls.Ā V = I x RĀ Ā Ā or Ā Ā I = V/R
The resistace of light bulbs is very nonlinear and decreases as the voltage drops due to the filament cooling down.Ā This probably does lead to a rise in current as the voltage drops significantly but not I think in the 1 volt range around the nominal 12V.
Modern electronic devices have power inputs which tend draw the power (Watts) they require irrespective of the supply volts so that the current increases as the voltage falls. Ā Ā Ā Ā Ā Ā I = W/V.
Just what the nature of the MX5 dark load is I know not but I guess itās a bit electronic so Gerryn is right that the battery wonāt last as long as the Ah rating would suggest.Ā
Standby batteries have Ah ratings andĀ an alternative constant wattage rating to allow for modern loads.Ā From my memory the reduction though was only about 10% .
If itās already let you down itās well worth getting the charging and battery checked now and a new battery if it is a few years old then you will feel confident about it.
Assuming the load W is constant and starts off at 0.02A with a fully charged battery at 12.7V = 0.254W
It will be 11.8V when nominally flat (potential but little capacity) so by then the current would be 0.254/11.8V = 0.0215A
So, there will be only a little difference in current (as there is only little voltage change) and hence there will be only a small difference in the number of days.
Being practical, as the original poster said, have a look round any long stay car park and you wonāt see many battery problems. Coincidentally, I started my sonās Mazda 2 on the drive today for the first time in almost 4 weeks as he is away and it never gave me a cause for thoughtā¦
If itās already let you down itās well worth getting the charging and battery checked now and a new battery if it is a few years old then you will feel confident about it.