15V at the battery...keep driving?

nostatic · nostatic's Garage

so the consensus seems to be that the alternator is going south, and I'm getting voltage readings of between 14 and 15.5V at the battery with the engine running. Tuesday it goes to TRE for an alternator rebuild, but what are the odds on making something go "boom" driving it this weekend? I brought it to work today since it had sat for 3 days and looked very forlorn...

Jeff · 10-10-2003, 03:40 PM

Don't know about Boom, but you could cook something. You may also want to check the front trunk for battery acid as it may have boiled over (Clean this with a baking soda water mixture, rinse and repeat). If you have a gel battery... never mind.

nostatic · nostatic's Garage

I didn't see anything at the battery last night, so hopefully I've avoided that so far.

81 930 · 10-10-2003, 04:01 PM

Seeing 14 to 14.5 V from the alternator/voltage regulator is perfectly normal. But 15 to 15.5 V is a bit high and could eventually fry your battery. Has it been creeping up on you recently?

Early_S_Man · 10-10-2003, 04:06 PM

Since your readings seem to vary ... I suppose it is a bit of a gamble. Do you feel lucky???

If the high end goes higher ... say up to 20 Volts, it could cause a multitude of problems, among these:

1. The factory alarm can fry and fail in the 'disable starting' mode ... a minimum of about 2 hours work to bypass the alarm and get the car starting again! This isn't a 'parking lot syndrome' problem ... when the alarm unit fails ... the engine DIES RIGHT THEN!!!

2. An Optima or other gel-cell battery can explode if subjected to an hour or so of 20 Volt charging! Probanly even more time to clean up and replace battery than the above mini-disaster!

3. The Bosch CDI can fry at those Voltage levels! Disabled until a suitable Bosch rebuild can be accomplished or Permatune unit installed!

Sorry to be so pessimistic, but reality hurts sometimes!

pwd72s · 10-10-2003, 04:07 PM

Okay, now that we've got this topic going...what exactly is "too much voltage"? 14.5? 14.7? 15? Where is the line when damage can happen?

Early_S_Man · 10-10-2003, 04:13 PM

Paul,

See above ...

Anything above 16 Volts is really risky! H1, H4, and H5 bulbs can burn out when surges occur, in addition to the above major problems. Of course ... no headlights as a surprise at speed in the mountains at night could be called a 'major' problem, too!

ronb · 10-10-2003, 04:21 PM

can you point to the best thread for hooking up a permanent voltage gauge / meter?

911pcars · 10-10-2003, 04:33 PM

Todd,
For the short run, you could connect a voltmeter to the battery and monitor the charge voltage. If it outputs at 15V+, you could turn on the fan, headlights/highbeams and/or any other electrical accessory to drop it down until you get over to the garage. See if that works. Make sure the battery still has water covering the plates. Keep electronic circuits OFF as Warren suggests.

To permanently connect a VM, you could connect the gauge directly to the positive battery post and to ground, but the wiring could get a little messy at the + post. An alternative is to connect it to one of the source posts in the fuse box and ground. Pick a fuse that's only active with the ignition ON. The voltage reading should be fairly accurate and will allow you to monitor system voltage while driving.

Sherwood Lee
http://members.rennlist.org/911pcars

Doug Zielke · 10-10-2003, 05:13 PM

Quote:

Originally posted by nostatic
Tuesday it goes to TRE for an alternator rebuild...

Hey Todd,
Don't you have any tools, man??
Isn't there someone near ol' nostatic that can help him?

nostatic · nostatic's Garage

lack of tools and time. The VR was 30 minutes and I could handle that. The alternator seems a bit more involved.

scottb · 05:59 PM

Todd: I just went thru this with my 84 (as you know). If you want to do a DIY, I'll help you out. It's not a complicated job, and we could probably have it done in a couple of hours. I have all of the necessary tools.

Send me an e-mail if you're interested.

Scott

rcwaldo · 10-10-2003, 07:33 PM

keep an eye (hand) on your battery temps. Feel around the sides every now and again while driving errands (or what have you). An overcharged battery will get warm to hot. Kinda scary IMHO

RoninLB · 10-10-2003, 09:06 PM

Quote:

Originally posted by rcwaldo
Kinda scary IMHO

it's all only BS elec stuff IMHO..

a quick wire volt gauge and using system loads to lower any "higher volts" is doable.. start with full fluid in battery..

and 15.5v is not a big deal to deal with. getting to 14.5 should be easy or carry extra water.. and start checking in an hour for a baseline in case you have to drive 500mi .......Ron

morganb · morganb's Garage

Nostatic,

Just after I got my car same problem, blew lamp bulbs, wrecked my battery and the wiring stunk from burning as I was driving after about 5 minutes. Luckily no premanant damage to car but required a new battery.
I suggest you get it fixed quickly.

Wayne 962 · Wayne 962's Garage

Also keep in mind that voltage spikes can be hard to see when you're driving. I had a similar problem with my truck - it took a long time and some replaced wire harnesses to fully recover (acid had burned through the wires near the battery)...

-Wayne

pwd72s · 10-11-2003, 09:48 AM

One tip for a cheap & quick way to test voltage while driving? Jeff Smith told me he bought a cheap multimeter, then hooked it to the + and - wires of a accessory plug in...leads long enough to place the unit on his passenger seat, can monitor voltage as he drives. I recently bought a digital voltage meter that plugs into the cig. lighter...also handy.