Why am i not getting 14.0 V from OBDII port

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Riad

Riad

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Germantown, MD
I've got 150 amp sequoia alternator with smaller pulley and beefier cables. Shouldn't I be seeing 14.0 volt? How do I troubleshoot? It fluctuates from 12.9 to 13.7 right now in normal driving condition.

Thanks
 
it's the way the 80 is wired. all of the voltage is pulled from the fusible links that connect to the battery terminal. voltage loss from that point to the rest of the body will bring the voltage down. so it may be 14v at the battery, it will progressively drop as you test voltage at points further from the battery. you could increase the wire sizes to reduce resistance. i don't know how the sequoia alternators work, but on the GM alts, they have a voltage sense wire that is used to 'sense' the voltage at whatever point the wire is connected to. I see 14.1v at the OBD port.

http://www.madelectrical.com/electricaltech/remotevoltagesensing.shtml
 
Yeah I have upgraded wires for the battery, starter and alternator. I think they are all 2 AWG. That's an interesting link, thanks for posting it. I don't have detailed knowledge on the sequoia alternator either; hopefully some one else can chime in and provide some insight. :cheers:
 
What is the voltage at the battery using a DVM at the same time being displayed in the Scangauge (at the same RPM)? There may be an offset between the two.
 
With a fresh battery I saw different reading as well with my Scangauge II. Always seems to show higher (around 14v) when I first get in the vehicle and lower after a long drive (mid to high 13's). I haven't seen anything in the 12v range though.
 
Get on it...chop chop..... :-)
 
Mr Cimarron said:
With a fresh battery I saw different reading as well with my Scangauge II. Always seems to show higher (around 14v) when I first get in the vehicle and lower after a long drive (mid to high 13's). I haven't seen anything in the 12v range though.
Click to expand...

That is the way it should work. The voltage will vary depending on; battery charge level, system demand/loads, motor RPM, etc.

Example: When the rig has sat, then started, a big load/draw is placed on the battery, the alternator has to deliver to replenish the battery and cover system loads, once the battery is topped up, it only has to deliver enough to cover system loads. This is handled by the regulator, it controls alternator output to meet demand. For the most part, alternator output is relativity low, if it ran full bore all of the time, would quickly smoke the battery.
 
Yeah can't do chop chop...:D these days I'm doing good trying to keep up :hillbilly:

Got home from work, got the DVM to the battery and I got 14.0 like split of a second then it stayed between 13.9 and 13.8 with AC and my electric fan running at full speed. So what does that mean? battery needs to recharge? Or I have a parasite in the system?
 
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Semi hi-jack, what should it read at the battery when the vehicle is not running? Mine measures 13.1v, which seems high for a 12v battery. Makes me wonder if my volt meter is off.
 
If you really want to know suck out some electrolyte in a hydrometer count the balls then add or subtract from that number depending on temp unless it is exactly 80 degrees
 
Tools R Us said:
That is the way it should work. The voltage will vary depending on; battery charge level, system demand/loads, motor RPM, etc.

Example: When the rig has sat, then started, a big load/draw is placed on the battery, the alternator has to deliver to replenish the battery and cover system loads, once the battery is topped up, it only has to deliver enough to cover system loads. This is handled by the regulator, it controls alternator output to meet demand. For the most part, alternator output is relativity low, if it ran full bore all of the time, would quickly smoke the battery.
Click to expand...


What Tools said!!
 
Riad said:
Yeah can't do chop chop...:D these days I'm doing good trying to keep up :hillbilly:

Got home from work, got the DVM to the battery and I got 14.0 like split of a second then it stayed between 13.9 and 13.8 with AC and my electric fan running at full speed. So what does that mean? battery needs to recharge? Or I have a parasite in the system?
Click to expand...

and what was scangauge reading at THAT time?
 
ok, that's a normal offset IMHO. I wouldn't worry too much about it.
 
The OBDII readers sometimes give you the choice of displaying OBDII voltage (i.e. what the ECU is reading and providing in the datastream) OR what the reader is measuring on the OBDII connector.

Either way you are taking a reading that is on the end of a bunch of wiring with various voltage drops due to the current draw and resistance of those wires/connectors etc.

Next throw in measurement accuracy which is likely to be no better than +/- 1 or 2 percent.

Finally many folk are using cheap/junk multimeters that came free at their local HF.

cheers,
george.
 
14volrs is OK

normative voltage on this cars range low 12.5 volts to 14 volts
12volts is low - even all diagrams are 12-24 volts as ISO standard

so if you reading 14+/- volts your alternator and the battery going well. now if you have more that 80amps you need to have a good wires and ground support to the battery. but 80 amps are more than you even need from this truck
 
I know I’m resurrecting a dead thread but im
Noticing about 1.4v difference at 2k rpm and lower between battery and odb2 scanner. I guess it could be there may be a couple of diodes in the path to the sensor with a 0.7v loss across them?
 
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