What's your volt meter reading when cruising around town? Options

[raynekat]

Just curious what the typical volt meter reading is:

1) when you're sitting at the stoplight

2) cruising down the boulevard at 3-4000 rpm

Trying to see if I'm seeing typical or low readings
Thanks

I just recently noted a low charging issue that I believe came down to an alternator/voltage regulator mismatch.
I was using a Bosch VR with my Motorola alternator.
Now I've switched to a Marchal VR and the charging voltages look better.
About 13.75 volts while cruising.

[raynekat]

Superhawk....I think you were dead on about that Lithium Ion battery not being "big" enough.
It just doesn't have the reserve to keep up with the electrical usage on the car.
This is what I measured on one of the big cables coming off the positive terminal on the battery.
The values you see listed below is the total reading I read off the clamp meter....not what each additional component added to the total (i.e. engine running with running lights on was 6.6A....the running lights alone were something close to 3A).

At idle (baseline): 3.6A

Add running lights: 6.6A (only about 3A added, Spoke's LEDs in rear, normal in front, with LED side marker bulbs)

Add headlights: 9.2A (guess the 914Rubber LED headlights are fairly energy efficient...added 2.6A)

Add front fog light: 16.1A (these are normal bulbs...about 7A)

Add rear fog light: 18.2A (again a normal bulb.....only about 2A added)

Add wipers on low: ~25A (the meter was really jumping around with the wipers)

At idle with wipers only: 8-10A (about 6A added)

So the 30 Amp-hr rating on the Lithium-Ion battery is not enough to keep up with all these loads turned on at the same time. I didn't even try adding the defroster fan or higher wiper speeds as the car (or built-in circuitry of the battery) turned itself off pretty quickly after I added the wipers and got the load up in the 25A range.

Luckily the battery always keeps a reserve allowing a couple of restarts after it shuts itself off. So the battery operated as advertised it seems.

Takeaway..... This battery is OK for race cars (autocrossing) and driving around town during the day in nice weather. Which is what I will likely only be doing. Any nighttime or distance driving and I'd want a different battery. I'll definitely be thinking about moving up to a 50-70 Amp-hr battery this Spring at any rate.

[Superhawk996]

Nice work and great information for the community. Thanks for taking one for the team! (IMG:style_emoticons/default/cheer.gif)

Yeah, that is definately too much for a 30Ah Li-ion battery.

So reported numbers are at idle, I know it would be hard to document running over time, on the road, but I'm 99% sure you will have two things occur:

1) Any battery (including Lead/Acid) will begin to lose cell to cell voltage as it discharges and current will drop accordingly according to Ohms law I= V/R where R is fixed by the components. Actually I'm 100% sure on this one!

2) Ultimately the battery managment sytem (BMS) will end up disconnecting the load (internally) to the battery so that the Li-ion battery doesn't completely discharge, which would harm the battery. On the way to that point, a Li-ion BMS MAY begin to throttle current to the load as cell voltages dip depending on how the BMS was designed to operate. I think it your case, it didn't throttle current since you said it allowed up to about that 25A draw and then just suddently disconnected.

Out of curiosity, did you get the current clamp around the alternator ouput wire (B+ that goes to starter)? I'm sure you're alternator is pumping out some juice to help offset the draw when you're running which explains how you are able to get more than say 1 hour of running time if you were indeed drawing 25A total on just the battery.

Alternator is 50A so in theory it should offset completely but the reality of stop & go driving is that you're probably spending more time idling than you think and at that point, the battery will have a hard time keeping up and you'll see the dimming that started the thread discussion.