Not a dumb question. There are a couple of things to know about that path though. Wiring a voltmeter into the 12V system would be pretty easy, but we want to see the HV battery and its 330V... I'd be a bit nervous about tapping into that system as its fairly dangerous to mess with it.

Second has to do with how rechargable batteries discharge. Alkalines and the old Rayovacs you used to use discharge so that the voltage falls pretty much linearly as they go down. But NiMH, and NiCd (not sure about Li-ion but they have their own issues) acutally hold their rated voltage as they discharge. Our battery probably starts with a voltage above 330V and falls a bit fairly quickly..... but then it would hold at right around 330V right up until it was nearly empty... then drop like a rock! So you'd get a guage that would tell you 100%-90% fairly well...but then it would stay near 90% until it died and that last 90% would look like it lasted a minute! Also whenver the generator kicks on and charges the battery you'd loose your ability to see what the charge was becasue you'd be reading the charging voltage (above 330V)

In order to see charge on this kind of battery you actually have to count the coulombs as they go into and out of the battery with an ammeter and you have to add them up. This is one of the reasons older laptop battery guages were pretty poor... the algorithms for how they discharge and how their capacity changes each time they charge weren't very well known at the time.

I can't guarantee all of that is perfectly accurate for our NiMH pack. I'm an EE and I've worked on battery powered systems for several years in handheld devices. I know about the little NiMH packs, NiCd, and LiIon, not the large ones. But the chemistry is bound to be similiar and likely so is the behavior.

 

Thanks for the reply, Tim. I figured it couldn't be that easy, or everybody would be doing it. I'm not smart like you EE's, but I've got friends who are used to diving into high voltage stuff (we build industrial equipment). But, if it wouldn't do me any good, that's the bummer.

Thanks, again!

Scott

 

The voltage swings are huge. I've drivin with a HV volt meter, and while Regen brake charging, the voltage can be as high as 424 volts.

Accelerating from a stoplight, the voltage can be as low as 270 volts.

424v ( charge ) to 270v ( under load ) within seconds of each other.

May be fun to watch, but with swings all over the place, not really useful info.
The resting voltage when you park ( key off ) may be pretty accurate. ???
Good thought though!

-John

 

I would love to try running a meter while driving. Can you give some more info on how you did it so I don't kill myself.

 

It was with Ford's Equipment, and a Ford Tech driving... I was in the passenger seat... you could tap the battery pack in the rear with something as simple as alligator clips, but do be careful... and I don't really see a lot of benefit from doing so... I already told you ( below ) what most people are curious about.