Recommend me something that tracks battery voltage/current draw over time?

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robinbanks

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I've an issue with a car battery being flattened seemingly at random, and suspicions that the charging circuit isn't operating effectively. Everything checks out whenever anyone looks at it; charging voltage with engine running is 14.5, parasitic draw is 20mA with engine off, so why the battery only registers as 25% full or less after a long run, and sporadically is found to be dead (8v) after being parked for a couple of days is currently a mystery

I want to get a track of voltage and of current drawn/taken by the battery over time so I can see if it's just a charging prob or if there is some occasional freak high drain when the car is off so I can start looking at possible causes..

But I've no idea what kind of kit could reasonably cheaply monitor these things and keep a regular history - in particular an ammeter that can pass and monitor the many hundreds of amps a 2.0 diesel requires for starting will likely be the tricky part..?

Dont mind a bit of DIY, build it myself with a raspberry pi, arduino etc but if there's something off the shelf for a hundred quid, great
 
Don't know of anything off the shelf, other than a midrange obd scantool that can keep history, but would need ignition left on to record anything.

There are (bluetooth ?) obd kits that can link to a phone via an app, but again only with ignition on.

What car is it out of interest ? I've known of a few Ford's with fusebox issues that give similar issues
 
2013 Ford Galaxy. The battery light illuminates on a red color occasionally when driving; it goes away if the engine is restarted (clutch in, long hold power, press power). It also goes away if one doesn't do the clutch in (just long hold power to switch engine off, then press power again - car motion keeps engine spinning so passengers barely even notice the restart), but interestingly it's much more likely to re-illuminate again if this latter procedure is followed.. as if the starter starting the engine has some different effect to the car momentum keeping the engine spinning while its control circuits reboot)

Other symptom is the dash display reliably warns "low battery" if one listens to the radio for a few minutes after switching off the engine - and as noted the Lidl/Oxford trickle chargers both assert the battery is only a quarter full immediately after switch off on a long run that should have charged the battery. I can use those same trickle chargers to fully charge the battery, take it for one short run, no battery light evident, but the trickle chargers then assert the battery is a quarter full again

Battery recently replaced, Exide premium. Behaves the same as the old battery (Bosch silver). I don't think the battery is at fault, though the charging circuit may be poor, and has ruined the new battery as it did the old. Haven't done a stamina test on either old or new battery (don't have a high amp tester)
 
Suggests a charge system fault to me.

Likely to be a smart charge system on that vehicle. Possible alternator issue, or wiring I think
 
How old is the battery?
Have all the battery connections been cleaned, positive and both ends of the earth?
Alternator drive belt condition and tightness?
 
Old Salt said:
How old is the battery?
Have all the battery connections been cleaned, positive and both ends of the earth?
Alternator drive belt condition and tightness?
Click to expand...
About a year. Battery ends were when the new batt fitted; other ends weren't checked

Belt condition is reasonable, been on at least 4 years but no chatter or squeal and tension seems good (has a tensioner)
 
carmanmemoranda said:
Not sure if yours is smart charge system, but I'd expect it to be. This link may give some info about it

Ford Smart Charge Diagnose

www.cartechelectronics.com www.cartechelectronics.com
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I think it may be, but haven't been able to find any concrete info. Do have an OBD tool somewhere that may give more. I recall reading that the battery icon in an SC car can be yellow or red for different meanings, but I've only ever seen mine red, which doesn't conclude much. Cheers for the link, I'll take a look at it!
 
I would add a temporary voltmeter, directly across the battery, but fused - so you can monitor the voltage when on the move. See what that shows up!

Voltage when measured at the ciggy socket, can vary wildly, depending on other loads.
 
I've got a starting point for diagnosis I think; check if it has a 3 pin plug on the alternator, and if so, check that the alternator kicks out 13.8v with the plug disconnected. Then find where the other end of the wires from that plug are (no idea where the PCM unit hides in this vehicle) and check they have good continuity and are electrically isolated from each other..

Then I'll look at getting a scope and watching the pulses on the command and feedback lines as load varies

Still thinking to monitor parasitic draw and voltage somehow when the car is off; even though the charging system seems not to do a good job of charging the battery it puzzles me how a low measured draw (20mA) can bring a battery from 12v to 8v in 48h; surely something must be waking up and drawing more
 
Wouldn’t hurt to clean the connections up especially both ends of the earth. Some obd diagnostic will let you monitor as you drive but as Harry says if you can rig a voltmeter to let you monitor it as you drive it may give an indication as to what is happening. If you could borrow another battery to try it may help isolate the problem.

Don't think its a good idea to run the alternator disconnected.
 
robinbanks said:
Still thinking to monitor parasitic draw and voltage somehow when the car is off; even though the charging system seems not to do a good job of charging the battery it puzzles me how a low measured draw (20mA) can bring a battery from 12v to 8v in 48h; surely something must be waking up and drawing more
Click to expand...

I'm sure you knew, but just to be sure...

If the battery was fully charged at switch off, then the battery would read 12.7 to 12.9v - not 12.0v, which is already flat..
 
The battery isn't fully charged at switch off; that seems to be one of the problems. What I'm saying is I can't see how a 20mA draw could take an 85Ah battery from 12v to 8v in 48h.. I'm wondering if there is something else that starts to draw more at some point. Bizarrely, for the most part (and in warm weather etc) the battery seems only ever to be charged to about 25% (whatever a AutoXS/Oxford trickle charger does to gauge that) which starts the car fine every day. Leaving the car dormant slightly longer means it's unlikely to start, or even power up

Old Salt said:
Don't think its a good idea to run the alternator disconnected.
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Me neither, I'm looking at disconnecting the smart charge plug for diagnostic purposes, which apparently causes the alternator to revert to standard behaviour; it's not disconnecting the alt completely, just the smart charge control wiring.
 
If the battery has been down to 8v a few times it's probably scrap. Might be worth £50 quid for a used alternator and a fresh battery.
 
If its a smart charge system it needs correct type of battery and alternator.

Be nearer 100/150 for the battery alone. Not sure I'd try second hand alternator but a new 1 won't be cheap either.
 
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