Weird battery voltage issues

Thenoob · December 11, 2015, 06:47 PM

Ok!

73 d18. 318 dodge.
Had a fully charged optima battery, threw it back in the winniebago.

Now, at initial startup, alternator putout at battery reading 14.8 volts
Go Inside, turn everything on, loghts stereo etc. Staying at about 13.8 volts. Ok cool.

Now once the coach is warmed up and engine is warm, I kick the idle Down. Boom immed drop to 11.3 volts. Within 5mins she's way down and won't restart.

Now, is it because the idle is set Too low that the alternator is not being able to give enough juice to maintain the charge once the idle is kicked down?? That would be my thought?

Rickf1985 · December 11, 2015, 07:49 PM

Battery is no good for one thing and idle is probably too low. Mostly it sounds like a bad battery. But if you left all of the accessories on at idle then the alternator is not going to be able to keep up at idle. Just lights and stereo should be no problem at idle though, the battery should have carried that for a long time alone. You need a good battery before you can diagnose anything else. Have the battery load tested.

DRMousseau · December 11, 2015, 07:59 PM

Yup,... I'd be lookin REAL close at that battery.

My alternator blew apart this summer,... I cut the belt to it, and ran a couple hundred miles with some stops here and there. Now this was daytime runnin', no lights, but that battery should carry ya a bit with no trouble even at idle,... not that engine speed has anything to do with jus runnin on a battery.

Alternator may not put out much at idle, but that 11v reading says your battery isn't much good, likely a dead cell. Get a good charged battery, let it rest from charging a bit, and measure BEFORE puttin' it in,... should be 12.6V-12.8V. Then try this over again.

LJ-TJ · December 11, 2015, 09:27 PM

Bad news my vote goes with the boys. You can check the battery but my guess would be to just buy a new battery. Hm?

Thenoob · December 11, 2015, 10:32 PM

I'd be bummed if that hella expensive blue top optima shoot the bed.

Just weird, I only turned on the lights and stereo at idle.
When the idle was going high during startup, voltage never dropped below 13.8-14.6

As soon as I kicked idle down it immed dropped to 11.3 and spiralled down to 10.2 within 5 mins at normal running idle.... Just with lights and stereo on

jeno · December 11, 2015, 10:47 PM

Could the alternator belt be lose?

UK-Winnie · December 12, 2015, 05:43 AM

Quote from: jeno on December 11, 2015, 10:47 PM
Could the alternator belt be lose?

It should still restart after just 5 mins though.

To check it out without spending any money pretty much any battery should do for a test run.

LJ-TJ · December 12, 2015, 07:38 AM

Well it might be idling to low. I think it should idle at around six hundred RPM after it warms up. I could be wrong. Do you have any idea what she idles at after she warms up? Hm?

Rickf1985 · December 12, 2015, 09:23 AM

10.2 is a dead cell. I hate Optima batteries. In my opinion they are overpriced junk. They made a big hit because they were the first out on the four wheeling scene with the AGM battery technology. I bought one and it did a lot worse than the Wal-Mart batteries I had been using. Never got another. Many of my wheeling buddies had the same experience with them. That was back in the late 70's when they came out. I have never heard much better about them other than in advertisements.

I have always recommended Odyssey batteries for longevity and performance. They Ain't cheap though! You get what you pay for.

http://www.odysseybattery.com/marine_battery_specs.aspx

Rickf1985 · December 12, 2015, 09:25 AM

WHOOPS

Goofed

M & J · December 12, 2015, 09:36 AM

No way Rick...

Rickf1985 · December 12, 2015, 10:18 AM

Yes, you saw it, my first mistake is 62 years! :)rotflmao
I was perusing the battery sites and I notice that although I always promoted Odyssey batteries I was not really into the total deep cycle thing at the time, I do see that Trojan has some nice deep cycle only batteries out there. Don't even want to know the price. N:(

LJ-TJ · December 12, 2015, 10:59 AM

Don't hold back Rick. Tell us what you think. :)rotflmao

D:oH! N:(

DRMousseau · December 12, 2015, 11:58 AM

Them Trojans ain't cheap,... I paid $300 for my last pair of 6V T105's.

Having handled thousands of various 6V and 8V deep-cycle batteries, I've dropped, broken, frozen and blew more than a few up. On the inside especially, Trojan has a lot to boast of and I've highly recommended 'em for years in deep-cycle applications. IMO, the T105 is the best they offer,... I prefer them over their other similar 6V batteries.

Only handled a few hundred 12V batteries, and I jus haven't had the same feelin's for any particular 12V automotive batteries,... 'cept I don't much care for SLA's, AGM's, or Gell's, unless absolutely necessary for some special need.

I like open cell lead-acid batteries as they are easy to maintain and watch over. A weak cell is as as good as dead, and I wanna know jus what condition each cells is in,... rather than jus general overall good or bad. Been quite interested in the recent developing lithium technologies.

AND WHY,... do so many set such low idle speeds?!? I always feel that if ya start your engine, and remove the battery,... it should still run with lights and acc. on the alternator alone. If NOT,... then the alt output is too low. I either bring up the idle a bit to full alt output and if it still isn't enough,... I get a bigger alt!

MotorPro · December 12, 2015, 04:48 PM

I have heard from a lot of people who had problems with Optima batteries. But I have to say that when I was racing dragsters every year I would have to put a new battery in the car. Then I bought an Optima. Ran it for 6 years and it was still starting the 15 to 1 compression engine when I sold the car. Guess I was lucky but it was by far the best battery I have ever owned.

Thenoob · December 13, 2015, 12:42 PM

What's an optimal
Idle rpm for the 318?

I'm going
To test it
Today and low idle with a good battery and see if that one drops as well, then I guess we will have an answer

Froggy1936 · December 13, 2015, 07:57 PM

I don't know who makes them But I have had very good service from Pep Boys Batteries They are not cheap but fair price I just brought my boat battery in for the winter and filled all the cells & put it on a charger @ 2 Amps (regulated) for about 3 weeks It never lit the fully charged light So I checked the hydrometer level 1300 1300 1000 1000 1300 1300 Oh Oo, Checked the Volts 8 Volts 2 center cells are kaput. Marine starting batt cost $80.00 when new in 2007 Will need a new one I also got 8 yrs out of 2 12V house batterys From Pep Boys Frank

Rickf1985 · December 17, 2015, 09:55 AM

Will it start back up with a jump and charge normally without the lights on? If so that sounds like a very heavy drain through the lighting circuit. I can't picture that much drain without smoke or blown fuses involved though so check all fuses again and if you find one check out what it goes to. The headlight switch has it's own internal breaker so I doubt it is in the lights themselves. Try turning the lights on for a short time and then feel around for any wires that are warm. There should not be any warm wiring.

DaveVA78Chieftain · December 18, 2015, 09:29 PM

Either a diode in the alternator is breaking down once it heats up or a alternator circuit wire or connection is opening up due to heat from the increased amperage with the lights on.

Description of the circuit here: http://dave78chieftain.com/Charging_Syste.html

Troubleshooting info here: http://dave78chieftain.com/Charging_TS.html