Battery checks OK but won't start genny

[MikeP]

Yesterday I tried to start the genny and just got solenoid chatter. I figured I had a bad battery; the shore charging is a xantrax smart charger. THe NL genny has a 12v start battery.

I disconnected the start batt and connected the genny start cables to the other 12V batt that I use for some light electronic loads; genny started instantly. THis morning, because I like to know exactly what's going on instead throwing money at stuff, I did a voltage check and a specific grav check of the "bad" battery. It had been disconnected overnight.

Voltage was 12.62, indicating fully charged. Specific Grav of all cells was at/above 12.70 at 80F; also indicating a good batt.

I don't have a load tester and was kicking around how to load test the batt when I figured that IF the voltage and spec grav is OK but the batt won't crank the engine, that WAS the load test. THe fact that the other batt spun the engine with no trouble indicates that all the connections/cables are fine (though I broke them all and cleaned/reinstalled them anyway).

So before I buy a battery - does anyone see a fault with my logic re the battery testing?

 

[yachtsmanbill]

I don't have a load tester and was kicking around how to load test the batt when I figured that IF the voltage and spec grav is OK but the batt won't crank the engine, that WAS the load test.

Cant beat that kind of logic Mike! Theres a bad tie connection inside somewhere... shoulda bought a Rolls for the generator! ;-)) ws

 

[jim rosenthal]

So how can the battery be fully charged and not start the generator? Is there a connection problem with one of the battery posts?

 

[yachtsmanbill]

The individual cells are soldered (leaded) together and can fail under load. Theyll still carry voltage and charging but any substantial load and the joint will fail open. ws

 

[rsmith]

Reconnect it and see what happens. you could have moved a bad connection. Put your volt meter directly on the batt lugs when cranking and see if it drops. I made up several sets of 6' 14ga test leads with aligator clips on them for doing this kind of stuff so I dont have to sit there and hold the meter leads.

 

[JLR]

Mike - not sure if you fiddled with the connections to the battery switch. After going through what you went through for a few years, I decided to pull the switch off the wall and check the ends of the cables. Turned out I had bad connections behind the switch and also on the starter end of the genset as well. Any movement of any of the cables gave me a false positve (i.e. a start) but over time, the voltage drop was too great given the cable conditions.

 

[REBrueckner]

" Is there a connection problem with one of the battery posts?"

or

" Theres a bad tie connection inside somewhere.."

Had that happen once....had to replace the battery....

 

[MikeP]

Thanks guys. Yesterday I opened/cleaned/remade all connections, including those at the switch as a first step. The battery was connected/reconnected several times with no change in how it acted. And the 12v electronics batt started the genny just fine.

SO.. just brought home a new batt. Checked the voltage and spec gravity before installing - essentially the same as the non-working batt. Hit the starter and the genny started right up. Clearly the other batt was bad as Bill described or perhaps the plates were badly sulfated and the actual capacity was just a fraction of what it should have been.

The batt is 3-4 years old; I can't recall. Most of that time it was charged with a ferro charger; for the last year it has been charged by a smart charger. Maybe the ferro overcooked it and that caused the issue or maybe the batt just wasn't all that good in the first place and 3-4 years is all you get. It was an Exide Nautilus. My new Maintenance Free ("Maintenance PROOF" is how they should be labled ) 12v start battery came from West Marine via a port supply account that a friend has.

 

[krush]

So how can the battery be fully charged and not start the generator? Is there a connection problem with one of the battery posts?

Because voltage and amps are different animals--and you need both to do work (power=volt*amp). You can put a bunch of potatoes together and get 12.5 volts.

 

[Trojan]

You can easily check 12 volts, but if one of the straps between two cells or between them all due to age is half missing or badly decomposed the current carrying ability will be greatly reduced. Check the battery voltage while you are trying to start the gen.

BILL

 

[MikeP]

So how many potatoes would it take to make up a good 32V bank?

And what kind, Russets? Adirondack Reds? Yukon Golds? Jeez, so much to research, so little time!

 

[67hat34c]

So you had a good day boating then. Found problem and fixed for around 1 Harley dollar or .10 boat dollars

 

[yachtsmanbill]

So how many potatoes would it take to make up a good 32V bank?

And what kind, Russets? Adirondack Reds? Yukon Golds? Jeez, so much to research, so little time!

I did the math.... 266 Russetts, or 307 Yukon Golds! ;-)) ws

 

[Boatsb]

I did the math.... 266 Russetts, or 307 Yukon Golds! ;-)) ws

What about the little red ones. I like the red ones.

 

[yachtsmanbill]

You lose ampacity when ya boil them tho...anyone nuke them ?? ws

 

[SKYCHENEY]

Only use the red potatoes on the positive side. The yellow ones go on the negative side.

 

[Boatsb]

Is that an ABYC standard?