Botched shore power & house battery

[Diatom]

Winter heater scheme brought shore power amperage perilously close to 30A.
Opened canvas the other day, greeted by the unmistakable bouquet of ozone + fried bakelite.
Female cord end & cockpit receptacle were cooked. No fire, but badly damaged, too hot to touch.
I suppose combination of old/crossthreaded ring + high amperage did it in.
No fuses blew, no breakers tripped.
Obviously unplugged shore, killed inverter, killed heaters.
Background items (fridge, brnkl, network) drained the house overnight, reads 9.7V.
Waiting on parts. Tried to recharge by idling Yanmar: tops up Thruster & Engine batteries but ignores House.
I gather from old posts here that ACRs disqualify a deep-discharged battery for safety (in case a short is responsible).

Couple of questions arise:
If I understand correctly ACRs govern charging by alternator only, no impact upon shore power charging?
So - upon repair/shore reconnect I should be able to recover House?
And - surely by design there is some manner of breaker/fuse between shore & AC panel? I would expect that a proper shore power connection in good condition should tolerate amperage up to 30A, whereupon a breaker ought to shut things down?
Before the cold snap - no heaters - I had noticed that LED on fem end of 50 foot 30A cord seemed a bit faint; blue-oval exterior courtesy lights seemed a bit dim; reverse polarity lights on both AC & DC panels glowed faintly when viewed straight-on. I guess these are warning signs? All batteries approaching EOL, replacement already scheduled.

/tmm

 

[marksandyham]

A high resistance connection in the supply circuit will cause a voltage drop to the load connected. On a resistive load like a heater this just reduces the voltage and the btu output goes down. Unfortunately those BTU's go to the connection that has high resistance and heats it up. This is the "the fire was caused by a space heater" headline.

If the connected load is inductive (motors etc) the current can go up causing the overcurrent device (breaker or fuse) to trip.

Another thing to verify once everything is back together is how much current is being drawn on the shore power when everything is operating. A circuit should only be loaded to 80% max. About 2800 watts if voltage is 120vac.

Most articles I read about shore power connections recommend they be check for tightness and heating on a regular basis.

A retired Navy man once told me they changed the World War 2 saying "loose lips sink ships" "to loose connections sink ships" He was an electrician.

 

[glider4]

Switched our shore power plug and inlet to a 30 Amp SmartPlug system a couple of years ago. Just to avoid your scenario. Not a perfect solution but much better than the conventional set up in my lay opinion. We leave our boat on shore power in the driveway from October to May with no worries.

SmartPlug B30ASSY 30-Amp Inlet Connector Combo Kit https://www.amazon.com/dp/B004PI8U5U/re ... 3MASX9EP3G

 

[Diatom]

Good point @marksandyham - the fundamental cause of the disaster is likely resistance at loose connection, not current draw of resistive loads. Bad habit: unplug 50' cord, coil it back to cockpit, leaving female end plugged in, probably incrementally disrupting tight connection. No more.

/tmm

 

[knotflying]

Your issue is not uncommon. The smart plug will often prevent this occurrence. Many times it is a poor plug connection or corrosion on the contacts. The smart plug has a positive connection with a grip hold on and a thermal connector. However improper connection of the wired to the male outlet behind the liner can also be the culprit. Make sure when installing a new plug, no matter what type, that the wired connected to the wall outlet are coated with some corrosion block and very tightly secured.

 

[BB marine]

If I understand correctly ACRs govern charging by alternator only, no impact upon shore power charging?
So - upon repair/shore reconnect I should be able to recover House?

The ACR's are not controlled by any charging source. The ACR's are regulated by voltage. If the shore power charger is charging and the batteries are above 11V and one of the batteries being charged reaches 13.0 for 90 sec or 13.6 for 30 sec the relay will close.

The recovery of the fully discharged house battery bank will require you to excite the battery bank for the charger to recognize it. This can be done by turning the cross over or parallel switch from the engine to the house bank on. This will tell the charger there is a battery there to charge. Once the charge is excepted, turn the parallel switch off and the dead house bank will charge. Confirm that the ACR's have the green light. If you have a separate charger and inverter the charger has three outputs and will charge each bank separately and the ACR's do not matter but will still close when the voltage requirements are met. The batteries are then charged as one imbalanced parallel bank. If you have a charger/inverter there is only one charging output and the ACR's function the same way as they do with the engine alternator.

As far as the 120V connection. Check the pedestal first for issues. Then the power chord. There was high resistance at the point of the heated connection. Loose connection , dirty contacts, loose connection at the receptical wiring connections.

 

[GaylesFaerie]

If your house batteries are FLA, you should probably do a load test and specific gravity reading on them to check their health if you can get them to charge. Draining them down to 9.7 volts is drastically below the deep discharge voltage of about 11.92V. Depending on how long the battery was in this state it can cause hardening and crystallization of the sulfate which will in turn form a permanent insulating barrier that can grow and get worse. You may still be able to charge the battery but its performance will suffer and it can damage your other batteries when connected via the ACR by an imbalance in their ability to take a charge. The charger will average its reading across the batteries to determine rate of charge which can result in over-charging your good batteries and negatively impacting them. If your house bank is shot, best practice is to replace them all. More knowledgeable folks here can add to these comments to keep me honest. Gary

 

[BB marine]

If you determine your house bank is in poor condition It would be wise to start over. If the batteries are relatively new and the length of time of the total discharge was not weeks I would give them a chance before condemning them. Based on your comment in previous post you claimed them to be EOL I am assuming "end of live" I would replace all and start with a fresh batteries. The type of battery you choose should be based on your use and expectations of longevity.

 

[Diatom]

Thanks Knotifying, Brian, Gayles - the fog is slowly lifting...
Brian you saved me a day of blind fiddling around, many thanks.
Quite the learning experience. I have a "Bliue Planet" which I think controls solar charging only, irrelevant to immediate fiasco. Then a TruePower Combi Charger + Inverter. Batteries: FLA but great timing, replacing next week anyway having Victron-ized the thing in preparation. (Yes Victron displays "deep-discharge" in accusatory red). If I can limp across the Georgia Strait I'll be OK.

/tmm

 

[FlyMeAway]

I will second the Smartplug reco. Have installed them in all of my boats.

It’s worth noting, however, that the newer Smartplugs no longer have the automatic thermostatic cut-off. Apparently the ABYC didn’t like that feature (for complex reasons I don’t totally understand / haven’t researched), so rather than fight it they dropped it. In theory though, the larger contacts mean that the plug is never a point of resistance for overheating.

 

[it4llc]

This thread has me considering installing the smart plug as well. I checked out their install videos which seem very easy. However, they say to tighten the hex screws to 15-20 lbs torque using the supplied hex wrench. How does one measure the torque using the little hex wrench? I've got to assume that most people go hand tight on these without overly cranking down, no?

 

[S. Todd]

it4llc: I have a couple of 1/4" drive torque wrenches that use hex key sockets (important to have in the world of bicycle mechanics). The last one I purchased for use on the boat (the Volvo reverse drive specifies a minor amount of torque on a hex head bolt when changing the transmission filter) I purchased from Tekton (a tool company that sells lots of tools that are made in the USA). I suspect you could do that install by hand tightening and trying to keep all the fittings consistent, but then you would not have an excuse to add to your tool collection.

 

[Submariner]

I highly recommend the Smart Plug. Easy upgrade.

https://www.letsgochannelsurfing.com/smart-plug

 

[it4llc]

I suspect you could do that install by hand tightening and trying to keep all the fittings consistent, but then you would not have an excuse to add to your tool collection.

Indeed indeed. And my torque wrench only goes down to 25lbs, so might need to buy an additional torque wrench as well. ;-). Good suggestion though - seems like an obvious one to have looked for in hindsight as well. 😳

 

[SassyRed]

INCH POUNDS not FOOT POUNDS I believe.
You need an INCH POUND torque wrench for that not your standard foot pounds wrench. Inexpensive amazon or Harbor Freight item

 

[it4llc]

Yes, that was 25 in lbs, but still not low enough....