Voltage readings

I saw in another thread that Jack had mentioned "left over surface charge" on batteries reading greater than 13 volts. I got back from a trip the other day- dropped the trailer where I park it and went back next day to retrieve some things and get ready for winterizing. Raised the top and then checked the little voltage meter I have plugged into cigarette lighter in trailer. it was reading 13.7. THis surprised me seeing as the trailer had set for 12 plus hours and the plates should have equalized out by then. Also- it had gotten pretty cold over night. I did not re-check with my good multi meter on the battery itself- and the little cigarette lighter receptacle always reads a bit high. Still- does this make sense? Does it mean my vehicle alternator ( brand new- for those of you who recall this issue earlier) is overcharging and integrated voltage regulator isn't noticing the state of battery charge on the trailer? I've got to haul it over the house this week and blow out lines and put in anti-freeze---so I will check again. But-I guess I never thought about what is regulating the charge to my house batteries while driving.

rick

Rick, I would be VERY surprised to see 13.7 Volts on a 12V battery, even right after being charged. I suspect the meter you were using was lying to you. And, if so, that's a pretty big error.

I think if your alternator was really able to raise the charged voltage that high, the batteries would be boiled dry.

- Jack

You may be right about the meter- I will double check tomorrow. Since i posted that I did some searching and most the info I am able to find says that my alternator on the tv would not be able to over-charge the trailer batteries. On the other hand- I just got back from dinner with a friend who did 15 years in the navy on subs, maintaining batteries, and he claims you can get it that high on a 12 volt battery dependiongon what each of the cells actually are.

Rick

I think the battery would have to be made of something different than the standard lead-acid design, which, when fully charged is 2.105 to 2.12V per cell, giving 12.63-12.7V in a 12V battery. One source I looked at said sealed AGM and gel cell batteries have a higher full charge voltage, in the 12.8 and 12.9V ranges. These are all "open circuit" (no-load) voltages.

I wonder if submarine batteries are designed to be "better"? It would make sense for them to be.

- Jack

Voltage

First let me let you know I know enough about electricity to keep from getting shocked........ But like hilltool I have received readings over 12 volts.
When we dry camp I use the cigarette lighter outlet to check the battery voltage level. I plug in a cigarett plug that has two wires to which I connect my volt meter. It is not uncommon for me to get readings above 13 volts. This was not just a one time for me. I've done this every since we bought this Hi Lo. Several times I see readings over 13 volts.
God Bless
Papa

You may want to read these articles about batteries, etc. The 12volt Side of Life (Part 1) or Deep Cycle Battery FAQ

Those are great links, Rich, especially the first one. They both mention an 80% discharge as being a full cycle on a deep discharge battery. A source I looked at the other day said to try to keep the discharge to less than 60% for best battery life. And, I hope everyone notices that batteries last longest when not discharged (used) at all! This seems a stupid thing to say, but it really means you should try to recharge a battery as quickly as possible after using it at all and you should try to get it back to a fully charged state when you do this.

- Jack

I checked today after raising the unit and letting it rest for about 5 minutes-and I got 12.4 at the batteries with the good multimeter( what do you figure the amp draw is on raising the top?). So.who knows? Its been 4 days with temps in the high thirties over night since I dropped the trailer- so that voltage doesn't surprise me but I did get that high reading the other day. I would have written it off to lingering surface charge if so much time hadn't passed.

These are sealed wet cell batteries- Delco, and i'm unclear how old they are. I did have that incident this summer where I burnt through the battery box top and it makes sense to me that i damaged a cell quite possibly while doing so. How that would relate to screwy voltage readings is beyond me....especially ones that are high----but most of this is beyond me anyway. i only drove about three hours on the way home and i really don't know what the batterys were at when I left after dry camping for four days. I had the solar charger on during the day but that could not have replaced more than 4 or 5 amps daily....still my readings were never below 12.3 during the time I was there. But, three hours probably didn't bring them all the way back. Tomorrow or the day after i will haul it to the driveway for a couple of days and feed shore power into it and get my winterizing done. Come spring I think i will replace with new group 27 batteries if they will fit ---probably COSTCO ----and start over. I've been following a lot of info from a book I downloaded on boondocking with an exstensive section on electrical and batteries. That author recommends NOT discharging below 25% of capacity and always bringing the batteries up to full charge the next day. So-that goes with what jack was saying- also. It also goes to the difficulty of depending on solar panels if you are using up alot of amp hours daily. Thus, another argument for a generator. My submarine buddy was, also, claiming you should discharge the batteries to almost empty twice a year to discourage memory and,I believe if I heard him right, help clear the sulfation off the plates. I'm not sure many would agree with that and i don't know as he is an expert---but it is an interesting view point he got , I guess, from hanging around batteries on a nuclear sub for a couple of years.

In the book I have, there is a table that estimates 8 amp draw for the furnace, but he may be talking larger RVs. Anybody have a thought on that?

Rick

I DON'T want to cast aspersions on your buddy, but lead-acid wet cells do NOT have "memory" problems. I believe the first of the two links Rich posted mentions that too. But, the batteries will exhibit an inability to fully charge (which is a bit like a memory effect in terms of usable runtime) due to sulfation. Batteries will sulfate if the electrolyte level is low or if they are not fully charged, as I recall.

Deep discharging lead-acid batteries tends to destroy the plates and can cause internal shorts to develop.

To my knowledge, the only batteries that have the memory issue are Ni-Cads. I wonder if subs use Ni-Cads now?

I still think the high voltage reading you had was due to left-over surface charge and possibly an erroneous voltmeter. 12.4V after the high draw in raising the top tells me you probably have batteries that are in pretty good shape.

- Jack

You may cast aspersions on him if you want. I do all the time. He does have some great sub stories , though.

Rick

I'll bet he has wonderful stories, and, since I know the Navy doesn't do things with equipment without a good reason, I'm really bothered by the concept of deep discharging the batteries. I suspect there's something going on here we don't understand.

- Jack

I will clarify with him- but his explanation the other night had something to do with clearing whatever residue there is in the plates ---but I will ask again on our Tuesday night gathering after DEADFISH POLO ( a canoe game...don't ask) for clarification.

That said- I hauled the trailer home yesterday to winterize it- and left it plugged in all night. Strange occurences continue to happen. So heres one- when i came out this morning it was reading 13.3-sensible for being on the charger. I turned the furnace on to warm it up because I needed to finish putting the couch back together on the inside (easier to get to water pump and bypass valves) and after the fan had been on ---it went to 13.5. So what do you think THATS about? On another note-I notice the DELCO sealed electrolyte window(s) were back to "green"- so maybe I should start depending on that little silly apparatus for telling me when the batteries are fully charged as they consistently turn green after a good , healthy, 12-15 hours on the converter/charger. And , finally, Jack. I'm going to experiment with manually raising the trailer with the manual pump just to show my thanks to you for all your sage insight the last 6 months. Is there a valve or lever I need to turn , first, like with a bottle jack?

Rick

I don't know about my "sage advice". I suspect it's often worth exactly what you're paying for it.

No valve or anything of that nature on my lift pump for raising. I just inserted the handle in the receiver and started moving it back and forth. Not much effort involved, but the top raised pretty slowly and I only raised mine about halfway up (so that I could easily get inside to look for something). Then, it lowered just fine by using the lowering switch.

This all happened at the RV repair place with a just barely alive battery.

Your voltage readings make absolutely no sense to me at all. The 13.3 after charging seems right, but 13.5, fan off and charger disconnected? That doesn't seem possible.

However, maybe I misunderstood something. Did you leave the charger connected? If so, the furnace fan would probably have reduced the charge in the battery (in spite of the charger). This would tell the charger to apply a higher charge voltage/amperage to restore the battery to a full state. Most chargers taper off the charging power as the battery reaches a fully charged condition.

Hopefully, I'm making sense here.

- Jack

Jack

No, you are correct in being confused. The shore power WAS engaged ---so I suspect you are correct in assuming the voltage kick was the converter/charger compensating for the draw down with the furnace on and fan kicking on and off. Been out working in it today trying to tidy up and get things ready for winter hibernation ( like finding three or four packets of food which would have made an attractive invite for mice...wife said she had cleared it all....) and running the lights etc and watching the voltages fluctuate as things are turned on and off. The LED lights make a big difference, there, as nothing seems altered when I turn one on but if I turn on a light with an older incandescent bulb I immediately see a difference in the readings.

My "junk" drawer is the one above the refrigerator and when I pulled it out today it just came apart. It isn't any different, for the most part, in other trailers, I know, but It is always a little disconcerting to see how badly the cabinets etc are often put together. I feel like I need to walk around with a glue gun and stapler half the time. Anyway- that gets on the lists for the some winter time re-building.

Didn't wok the "pump" yet- but I am looking forward to it. Then, I can safely pull my batteries for the cold months and leave the cables accessible for a jump.

rick

Up where you live, I imagine it is prudent to pull the batteries for Winter. Reading the link Rich posted, you do not want a battery to freeze.

I think you'll find that once you take care of all the "defects", you'll really start to enjoy your trailer. I know I have.

- Jack