What would cause rapid heating negative pole on 12vdc battery? - Page 1
Forum section: electronics / beginners

author: caegear
author_rank: Contributor
timestamp: August 08, 2016, 07:55:02 pm
content: Hello all,I have an outboard engine that I want to understand. It is a Mariner 40hp 1988 model, and it is operating just fine. At least I think it is.The only little thing I am not completely sure of, is I noticed a rapid increase in temperature on the starting batterys negative / ground pole after repeated starting attempts.Background:I had used the battery (Exide Start / Stop branded) to run a bilge pump, and had to recharge it before starting the outboard. I noticed the starter motor had trouble turning the flywheel, but after several attempts where the flywheel would ony turn once pr. attempt, outboard did start as normal. Then I disconnected the battery to move outboard, and noticed the negative / ground pole and wire connected to the battery was very hot. Maybe 40-50 degrees Censius.I then did a test on the battery itself, and found it was just vbarely above 12vdc (12.3v). I hooked up the charger again, and after some 20 minutes the charger felt the battery was full. Voltage on battery was 12.6v, and when attempting to start outboard again same thing happened. Starter motor would only turn flywheel a couple of times, and then only barely one turn pr starting attempt. Negative was hot as before.I gathered I had ruined the battery by using it to run the bilge pump (overdischarged it), but since I could not completely rule out faulty charger I went and bought a new starting battery and a better charger with a separate "Desulfication mode" / "Repair mode".New battery took some ten hours to charge fully with new charger. New charger did not perform any different on the old battery. When I set it to "repair" mode, it quickly exited that mode and went into regular charging mode, but displayed an icon indicating it was charging a motorcycle battery (!). I would also do the "motorcycle thing" if set to "automatic mode", but if set manually to "car battery mode" it would stay there and claim battery was fully charged after some 10 minutes (still only 12.5 - 12.8v on the battery).Now. I dont plan on using the Mariner 40hp as I have a 70hp Johnson. My new battery spins the 70hp Johnsons flywheel like it was paper. I am curious if the new battery will spin the Mariner as well, but I am unsure if it was indeed the Bilge-pump that destrøyed the old battery or if there is something wrong with the Mariner.Question:Is there a common condition where a circuit (that could possibly be embedded in the Mariner) would build up heat like described above on negative side of battery that can destroy a battery?How likely is it that I will ruin the new battery if I try to use it to start the Mariner? Is there a test I can do (simple) on the negative or positive side on the mariner to rule out a potentially "batterydestructive" error?Sorry if this is a stupid problem. Batteries are so expensive, and I dont want to ruin the brand new one

author: Gyro
author_rank: Super Contributor
timestamp: August 08, 2016, 08:03:38 pm
content: Well my first guess would be a failure of the end cell of the battery - the one that the negative pole goes straight into. Either that or a bad (high resistance) connection on the negative clamp and the pole. I think it would have to be one or the other.If the battery has filler plugs (they often do in some form even if 'maintenance free') then you might find that the electrolyte level in that cell has dropped too low, increasing its internal resistance.

author: caegear
author_rank: Contributor
timestamp: August 08, 2016, 08:13:41 pm
content: Thank you Gyro! That sounds like reasonable scenarios. I am guessing the cell is down. Now only thing I would like some input on is wether the running af a Bilge-pump (some 5A) on and off for two weeks (im guessing three times on pr day (it turns on automatically when water level rises)) could have caused a collapse of the cell directly wired to the negative pole, or if the hookup and starting attempts (either with good or bad connection on the negative pole) on the Mariner could cause the cell to break down? Could it be the negative wire from Mariner is bad at some point and could this cause cell closest to negative inside battery to have its levels drop? (Can high resistance on negative side in Mariner ruin / deplete cell on a / the new battery?)Thank you again

author: Gyro
author_rank: Super Contributor
timestamp: August 08, 2016, 08:33:40 pm
content: You're welcome.In electrical terms, there's no difference between the negative end cell and any of the others, so it is probably just luck of the draw. I suppose there could be physical factors, eg, the mechanical clamp squeezing that end of the battery a bit too tight, or vibration at that end, but as I say, probably luck of the draw - one cell is always going to die first in a battery.Due to the chemistry, the electrolyte in the cells reduces as the cells discharge and increases again as it is charged (gassing produced by overcharging is simply Oxygen and Hydrogen being evolved quicker than they can recombine into water). A long slow discharge over several weeks could well 'dry' out an already dying cell to the point that it then gets very hot on a sudden heavy load (starting).If you still have the old battery you might try getting to the fillers. Some distilled water added to the dried out cell might still get you some useful life out of it as a backup. NOTE: in the confined space of a boat you need to be particularly careful that gasses can't build up after you've messed with it!

author: Seekonk
author_rank: Super Contributor
timestamp: August 08, 2016, 09:16:02 pm
content: Was that 12.8V while charging? Then I would have to go with the bad cell theory.

author: caegear
author_rank: Contributor
timestamp: August 08, 2016, 09:44:37 pm
content: Gyro: Thank you again! Everything points to me killing the cell on the Bilge-pump as everything worked fine before that. Even if I in the meantime disconnected outbord and battery from boat and installed a Bilge-pump and weeks later came back and mounted outboard and battery on land and then had this heat-thing going.I do have the battery, and Ill try to get to the cells tomorrow. It is a "maintainance free" battery, so Ill have to fiddle with the plastic to get to the cells.Seekonk: Thank you! Yes charging capped at about 12.7-12.8 maximum. Charger figured it was a "motorcycle" battery if left to decide, and Im guessing one cell is 1-ish volts and that loosing the one would drop the pack from "car" to "MC" in the chargers algorithm.Ill get back to you all if I get to the cell, and after Ive tried the fresh battery on the Mariner. Hopefully it will work just fine. Ill seat cables firmly and check wires before trying. With any luck Ill be able to test compression on both cylinders using the new battery

author: batteksystem
author_rank: Regular Contributor
timestamp: August 09, 2016, 01:41:14 am
content: Quote from: caegear on August 08, 2016, 07:55:02 pmheating usually mean high resistance, maybe checking the battery terminal and ensure the connection are okay?

author: Brumby
author_rank: Unknown
timestamp: August 09, 2016, 04:24:39 am
content: Quote from: Gyro on August 08, 2016, 08:03:38 pm+1

author: Totalsolutions
author_rank: Contributor
timestamp: August 09, 2016, 11:56:58 am
content: Battery terminal posts are lead. Lead has a bright shiny appearance when cleaned and polished. There are tools available to clean them. Then degrease with IPA (really, thats what I do), then clean the cable terminal to with the same tool. Tap terminal onto battery post and tighten up.Sent from my GT-N7100 using Tapatalk

author: helius
author_rank: Super Contributor
timestamp: August 09, 2016, 01:25:05 pm
content: It's more typical for high-current connections to be treatedwithgrease to prevent corrosion.http://www.w8ji.com/dielectric_grease_vs_conductive_grease.htm

author: SeanB
author_rank: Super Contributor
timestamp: August 09, 2016, 01:53:07 pm
content: With a marine battery I would guess you have a battery with captive nuts in the posts. Most likely cause, if the cells are not failed or low in water, is that the terminal internally has cracked, leaving only a small area of lead to carry the starting current to the motor.If that is so then there is no fix. Remember next time that the soft terminals are very fragile and easy to crack internally with almost no external damage visible.