Why is the battery post hot

[Vern]

Haven’t been able to get the roadster out in a while. When I tried to start it, it didn’t want to crank like usual so I decided to put the battery charger to use. When I touched the negative post to put the clamp on, it was very hot. Why’d this happen?
Thanks in advance.

[nkaminar]

Resistance. Take the connection off and clean the post and the connector with the wire brushes that are available at the auto parts stores or your pocket knife. The metal should be shinny. Then use a little dielectric grease on the connector and post and reassemble. Smear a little of the grease on the outside of the connector.

The lead that the post and connector are made of will oxidize after a while and the oxide is not a good conductor, adding resistance. If the connector is brass it will also oxidize. The dielectric grease, available at the auto parts store, will keep moisture and oxygen out.

[JoeCB]

clarification please. Was the battery terminal hot before you attached the charger clamp? (very strange)or was it hot after you charged the battery (not unusual, poor charger clamp connection) . You said that it was hot when you went to put the clamp on ... what clamp? the charger clamp or the car battery cable clamp?

Joe B

[Vern]

The terminal was hot to the touch before I connected the charger. There’s a on/off switch on the negative side with a knob that screws down to connect the system.

[JayJay]

I'm with NK, sounds like you have some resistance between the terminal and the wire, which heated up when you tried to run high amperage during starting. Pull both terminals, scrub them thoroughly, and retry.

[Ordsgt]

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I had used one of the battery disconnects you described and found that it had a tendency to fail due to corrosion inside the screw. It was not visible on the outside of the disconnect. It would actually get bad enough that the starter could not get enough amperage to turn over. I finally discarded that type of switch in favor of the on off that mounts near the starter.

[nkaminar]

I think Ordsgt is on to the problem. I will second what he said.

[Joe K]

Most petroleum grease is varying degrees of dielectric.

My grease of choice for CONDUCTION is "No-Al-Ox."

Grey, its a grease that contains graphite - a conductor. The grease was originally developed for use with aluminum wiring, which for a while was a vogue in domestic house wiring. It was a little while before they discovered that aluminum "skin-oxidizes" which increases the resistance of binding posts or wire clutches. Many houses burned down before the code recognized the issue and required at least a conductive grease.

In this area your electric service is likely large diameter aluminum, but the rest of the house is likely copper. One "butters" the landing lugs with No-Al-Ox for the aluminum wire the diameter of your thumb.

But you can use No-Al-Ox on any wire - and battery cables are just the place.

I give the post a quick spray after assembly with the die-electric spray - to keep corrosion "mounds" from forming on the battery top.

Joe K

[CT Jack]

Majority of opinions are basically saying get rid of the ON/OFF switch, clean the cable and battery post, and connect the cable directly. The battery cable on/off type switches are notorious for causing a high resistance connection.

[nkaminar]

Depends on the switch. The ones for marine use are generally good quality but I have had AC switches and connectors on my boat burn up.

[stevemclark]

Get this cleaner,Walmart under $2 or from most parts storeshttps://www.walmart.com/ip/Money-Envelopes-for-Cash-Barrier-Battery-Pile-Brush/15258922329?classType=REGULAR&athbdg=L1700&from=/search

[joncrane]

A battery on off switch is another gizmo in the series that can create issues. I concur with cleaning the battery posts, tightening the connections and smearing with dielectric grease.

Consider using a 25 Amp fuse on the circuit for the car with one of the kits that attach to the Starter cable. If you the car for prolonged periods simply pull the fuse up to disconnect the circuit. Just another safety feature.

I do not use a battery maintainer trickle charger. Do not trust 110 V going to the car battery over long periods of time.

My thoughts
Jon

[nkaminar]

The modern maintainers with desulfator will prolong the battery life and not overcharge it. Especially good if the car is not driven for a while. Having anything plugged into an AC socket incurs some risk of fire, but with the modern battery maintainers the risk is very low.

[Phil Brown]

Originally Posted by nkaminar

The modern maintainers with desulfator will prolong the battery life and not overcharge it. Especially good if the car is not driven for a while. Having anything plugged into an AC socket incurs some risk of fire, but with the modern battery maintainers the risk is very low.

Yes, far lower risk than those cordless tools getting recharged that everyone seems to have on there chargers constantly

[JayJay]

Forgive my ignorance, but if the resistance was in the switch, wouldn’t the switch be hot, not the battery post? Having said that, any switch is a possible location for failure versus a solid cable.

[rotorwrench]

If the OP had been running the starter, the cables and starter can get pretty warm just from the amp flow between the battery and starter. 150 to 200 amps of current can flow there depending on conditions. All cables have some resistance but the larger the cable gauge size the less the resistance will be. Make sure the cables are still well connected to their terminal ends and to the frame, starter, and battery. Any loose terminal ends will cause resistance as well as any signs of corrosion in the assemblies. Crimped terminal ends are common and some crimp types aren't very solid. Cable construction quality plays a big part in how well a 6-volt system will function. Junk cables will give junk performance.

[nkaminar]

Rotorwrench brought the subject of crimped connectors. Good crimped connectors are air tight meaning that all the connectors are pressed together and deformed so that there is no gap between them. As part of an engineering class we sectioned crimp connectors and examined them under a microscope. The bad ones, caused by bad crimping tools, were bad. The good ones were crimped with good quality crimping tools.

[ModelA29]

Originally Posted by rotorwrench

...... All cables have some resistance but the larger the cable gauge size the less the resistance will be. .... Cable construction quality plays a big part in how well a 6-volt system will function.

That points out another "problem" with most As. The battery cables have been replaced with 12V ones. Basically it takes twice the amps @6V to do the same work of 12V. Higher amps requires larger diameter wire.


For a 6-volt battery system, a 1/0 gauge (0 gauge) cable is recommended. While a 2/0 (00 gauge) cable is even larger and may be preferable, it is not strictly necessary. Some part suppliers may offer 12-volt 2-gauge cable, which is incorrect for a 6-volt system.


https://www.batterycablesusa.com/battery-cables

[Bruce of MN]

My A started fine for several years, then got stubborn. The cable to the starter turned out to be 4.5 AWG, based on diameter. I bet it got hot! I did change it.

[trulyvintage]

If a battery terminal or post is failing
inside the battery, it will cause heat
to build up, the battery can catastrophically
fail and explode.

Jim