Dead Battery
02-06-2018, 05:34 PM
#21
Senior Member
what I do to test a charging circuit on modern cars
1) meter on DC volts - car off - test at battery post. look for 10.5-12 volts. anything less than 10.5 unless is below 40 out I worry a bit if below 10 I know it's lost a cell.
2) meter on DC volts - car on - headlights on - AC on if possible - radio on - test at battery post - look for 13+ Volts. often with that much load it's closer to 14 but not always. Newer cars use a variable field effect alternator such as it varies the output voltage and amp to match the needs of the car.
3) same conditions but tested at the battery cables. If test 2 showed 13.5 volts I should see 13.5 volts here too - if it goes up to 14 or more I intend to clean the cables
4) set meter to AC - car on, lights on, ac on, etc - test at battery posts again. Look for less than 1 Vac. Ideally it should be 0 but it won't be. AC shows there is some ripple getting through the diode pack on the alternator - a little is OK. Much more than a volt tends to be bad on lead acid batteries (including the newer AGM systems). Also it shows the alternator is starting to go bad or is bad.
1) meter on DC volts - car off - test at battery post. look for 10.5-12 volts. anything less than 10.5 unless is below 40 out I worry a bit if below 10 I know it's lost a cell.
2) meter on DC volts - car on - headlights on - AC on if possible - radio on - test at battery post - look for 13+ Volts. often with that much load it's closer to 14 but not always. Newer cars use a variable field effect alternator such as it varies the output voltage and amp to match the needs of the car.
3) same conditions but tested at the battery cables. If test 2 showed 13.5 volts I should see 13.5 volts here too - if it goes up to 14 or more I intend to clean the cables
4) set meter to AC - car on, lights on, ac on, etc - test at battery posts again. Look for less than 1 Vac. Ideally it should be 0 but it won't be. AC shows there is some ripple getting through the diode pack on the alternator - a little is OK. Much more than a volt tends to be bad on lead acid batteries (including the newer AGM systems). Also it shows the alternator is starting to go bad or is bad.
02-07-2018, 04:47 AM
#22
Senior Member
02-07-2018, 08:16 AM
#23
Member
Go to Amazon or wherever and search for an ac/dc clamp ammeter (like the Craftsman digital 400A AC/DC Clamp 82369, it must say DC or it won't work for this application). Set it to DC Amps, clamp it around the positive battery cable, and viola... it'll show you the current. When the engine is off, it should show negative current (ie away from the battery). When the engine is on and the battery is charging, it should show positive current (toward the battery). If you see negative where you expect to see positive, rotate it 180 degrees on the cable. When the truck is off, any more than an amp or so of parasitic draw is worth investigating as a problem.
At rest I'd expect the battery to show 12.6 - 13.2 volts depending on how long ago the engine was turned off. Voltage will drop to 10V or even lower when the engine is cranking, and then immediately recover to something over 14V for charging, and as battery terminal voltage increases and charging current decreases, a smart charging system (like the electrical chargers in most boats, for example) will start reducing output voltage in order to avoid forcing current into the battery beyond full charge and thereby boiling water out. The alternators on my boat (twin 375HP Volvo diesels, 3 alternators total) put out 14.4v at all times, but only run for an hour or 2 before the batteries go back on the electrical charger.
If you don't want to drop 100$ on a clamp meter, many boat mechanics will have one. I keep one on my boat, which has 8 batteries on it, which means that one of them is always at some degree of failing.
To isolate your problem, look at the current when the engine is off, and have a helper start pulling fuses until the current changes noticably. That's the circuit I'd start investigating first. If you're lucky, it's not the last fuse you pull.
At rest I'd expect the battery to show 12.6 - 13.2 volts depending on how long ago the engine was turned off. Voltage will drop to 10V or even lower when the engine is cranking, and then immediately recover to something over 14V for charging, and as battery terminal voltage increases and charging current decreases, a smart charging system (like the electrical chargers in most boats, for example) will start reducing output voltage in order to avoid forcing current into the battery beyond full charge and thereby boiling water out. The alternators on my boat (twin 375HP Volvo diesels, 3 alternators total) put out 14.4v at all times, but only run for an hour or 2 before the batteries go back on the electrical charger.
If you don't want to drop 100$ on a clamp meter, many boat mechanics will have one. I keep one on my boat, which has 8 batteries on it, which means that one of them is always at some degree of failing.
To isolate your problem, look at the current when the engine is off, and have a helper start pulling fuses until the current changes noticably. That's the circuit I'd start investigating first. If you're lucky, it's not the last fuse you pull.
Last edited by White 1; 02-07-2018 at 08:37 AM.
02-07-2018, 09:32 AM
#24
I had an issue with my battery a few months back. Kept getting a battery check light driving and took it in. Turns out a cell was dead and they replaced the battery for free. Still got the check light for a week or two after (occasionally) but I haven’t seen it since.
This is a 2016 F150 and the issue happened in September 2017. After I drove for around 15-20 miles (30-35 minute trip) the new battery hasn’t had any issues.
This is a 2016 F150 and the issue happened in September 2017. After I drove for around 15-20 miles (30-35 minute trip) the new battery hasn’t had any issues.
02-09-2018, 09:08 AM
#25
Since smart charging came in around 2000, the PCM controls the operating voltage. Previously, the alternator performed that function. Battery voltage since smart charging has only been based on battery temperature. The colder battery, higher voltage. Nothing to do with load. If load exceeded max alternator output, then yes voltage dropped. Voltage range with the smart charging system was 13.2 - 14.7v.
Then comes BMS (battery management system) which still uses battery temperature but also now considers fuel economy or engine efficiency. So at idle which the engine is not efficient and if all parameters are met, the BMS can drop battery voltage all the way down to 12.3v. However, max voltage can be applied above 15v but generally only seen while coasting during high efficiency. There are a handful of upper/lower ranges and each range is selected based on battery temperature, battery health and engine efficiency.
One day the vehicle could be operating under one set of ranges, the next another set. Without knowing the proper PID's, one will not know the current selected range. To force the vehicle into what we call standard operating range which operates in the 13.2 - 14.7v based on battery temperature, the best method is to disconnect the bms sensor (battery mounted or hall sensor). This forces the vehicle to operate in default standard mode.
Then comes BMS (battery management system) which still uses battery temperature but also now considers fuel economy or engine efficiency. So at idle which the engine is not efficient and if all parameters are met, the BMS can drop battery voltage all the way down to 12.3v. However, max voltage can be applied above 15v but generally only seen while coasting during high efficiency. There are a handful of upper/lower ranges and each range is selected based on battery temperature, battery health and engine efficiency.
One day the vehicle could be operating under one set of ranges, the next another set. Without knowing the proper PID's, one will not know the current selected range. To force the vehicle into what we call standard operating range which operates in the 13.2 - 14.7v based on battery temperature, the best method is to disconnect the bms sensor (battery mounted or hall sensor). This forces the vehicle to operate in default standard mode.
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White 1 (02-09-2018)