Battery Trivia

BrianZ

The specific gravity of a fully charged golf cart battery (such as the Trojan T-1275, to which I just upgraded) is 1.275.  And if you move the decimal point one place to the right, that also happens to be the full charge voltage (as well as model number of my battery).

Mine was a bit depleted when I got it, at about 12.4V, but after leaving the T@B plugged in for a few days, then battery switched off overnight, it was reading 12.8+ Volts.  So, who said the converter can't fully charge a battery?  I haven't checked specific gravity yet, but that's on my list.  I also picked up a Noco Genius G7200 charger for periodic equalization & charging at the proper manufacturer's voltage of 14.8V bulk mode, since it has a cold charging mode which delivers that voltage.

Mostly, I'll use the Noco charger to maintain the old battery for backup.

db_cooper

I recommend you put the Noco charger on there and see how long it takes to finish. Just because you have a surface charge reading of 12.8 from the onboard converter doesn't mean there's not more room for some amps.

I find it takes my battery tender (max 3 amp per hour) overnight to fully charge after being "fully" charged by the converter. YMMV

BrianZ

Good idea, @db_cooper.  I'll unplug it overnight, then check voltage again & specific gravity, then run the Noco charger, then recheck specific gravity, and see how things compare.

BrianZ

Ok, @db_cooper, I unplugged last night, so the battery sat for more than 12 hours disconnected.  I then checked voltage and specific gravity, and here are my results:

12.88 V using digital multimeter.
12.9 V using T@B SeeLevel meter
Cell 1 SpGr = 1.285
Cell 2 SpGr = 1.285
Cell 3 SpGr = 1.285
Cell 4 SpGr = 1.285
Cell 5 SpGr = 1.285
Cell 6 SpGr = 1.280

Do you still see any point in my connecting the Noco G7200 charger when these measurements indicate this new battery is already fully charged?  The specific gravity was measured with a refractometer, which is the reference method, and the values are higher than what the manufacturer indicates is normal for a fully charged battery (1.275) at 77°F (temp was 76°F).  Fluid levels were exactly where the manufacturer says they should be (1/8" below the bottom edge of the plastic sleeve) in all cells.

If I did connect the charger, how would it indicate whether or not the battery was fully charged, and would that be any more reliable than these measurements?  Conversely, is there any risk of overcharging & damaging the battery?  Guess I need to read the charger manual.

BrianZ

Well, I found this on page 26 in the Noco G-7200 charger manual..

So I decided to try the new charger on our one year old group 24 Deka marine/RV battery, which has been sitting in our garage for the last week since installing the new Trojan 1275 in the T@B.  First I measured voltage and specific gravity:
12.80 V by digital multimeter
Cells 1-6 SpGr all = 1.280
All cells with normal water levels.

Connected the charger to battery, plugged it in, then set mode to 12V normal & watched..
Self test lights flashed then 25% charge light slowly pulsed on & off for about 30 seconds, then I could hear bubbling in the battery as it moved quickly through 50% light lit, then 75% lit, then 100% lit green, where it stayed.  All this happened in less than a minute, and I assume this was how long it took to progress through its diagnostics & decide charging was unnecessary.

This was the battery that came with our year-old T@B, which we have used on eight camping trips during the last year, all with hookups, no boondocking, and otherwise plugged in all the time with battery switch on, and 13.6V usually showing on the converter-charger.

Based on these results, I think I will skip trying to charge the new Trojan battery any further right now, although I'm sure we will need to put it to use after our first boondocking trip next month.  We might even have a dry run while parked at home for testing the frig & Alde on propane.

db_cooper

Sounds like your converter is doing a bang up job of charging compared to mine.  I leave our battery (2 GC) isolated and on the battery tender, so waiting for it to top off is not much of an issue.  The specific gravity checks are surely right, so I'm sure your right that you are topped off. 

Sharon_is_SAM

@BrianZ, if I read your post correctly, the recommended charging voltage for your batteries is 14.8 V.  I don't think the converter gets that high, but you proved that you can fully charge over a few days.  The smart charger that delivers the proper voltage for each stage would probably just hasten your charge time. 

BrianZ

Thanks for your comments, @db_cooper & @Sharon_is_SAM.  I may have only proved that the converter is adequate if you only use hookups, since we've never really deep cycled our battery with significant discharging, although the new Trojan was down a little to around 12.4V when we got it.  So, I guess it can do an adequate job, given enough time & if already in good condition.  I don't think the converter ever went into bulk mode at WFCO's 14.4V though, plus as you pointed out, Trojan says 14.8V is proper.  Since the new charger uses 14.8V for a cold charging mode, I'll likely make use of that after boondocking.  Plus, the converter doesn't do equalization as far as I know, so I can use the charger for that some day when specific gravity values get too low or varies between cells, according to Trojan's maintenance sheet..

"Trojan recommends equalizing flooded batteries (NEVER AGM or Gel batteries) only when batteries have low specific gravity, below 1.235 or wide ranging specific gravity, > 0.030 points between cells, after fully charging."

Sharon_is_SAM

@BrianZ, just as you mentioned, we charge our AGM via our Battery Tender Power Tender smart charger to make sure it is full between trips and storage.  

ColoradoJon

The onboard WFCO converter certainly can charge the batteries to full, they just are inefficient at doing so.  The absorption phase voltage is very low so it cannot push the amps into the battery very well.  Given enough time it will, but you are much better off using an external charger that is designed for these batteries.  I don't think anyone ever said that it can't fully charge the batteries.

BrianZ

Well, I discovered a new use for our Noco 7200 battery charger..

..when my DW parks car in garage, turns off engine, then turns key back to ACC to listen to music on the radio, leaves car & gets distracted.  Then next day cannot find her car keys anywhere, until looking in the car which will no longer start!  

Fortunately, it successfully completed the full charging cycle overnight.  And it was nice to not have to string together two sets of jumper cables to reach inside the garage & then go on a long drive just to recharge the battery.

klenger

This seems to be an old discussion that popped back to life again.  That being the case, I'll add my comments.  I do agree that the WFCO converter will fully charge the battery over an extended period of time.  While I don't understand how battery chemistry works, it seems that a constant supply at lower voltage (thus lower current) will supply the needed energy to fully charge the battery, ... it just takes more time to do this. 

If you camp with hookups all the time, then the WFCO converter will work just fine and not likely toast your battery.  If you are camping off grid, and attempting to charge using a generator, then a good battery charger that provides a bulk charge at ~14.4 VDC will drastically reduce your generator run time.  I strongly encourage anyone taking this route to invest in a battery monitor system (~$200) so that you know exactly what the battery state of charge is at all times.  The combination of generator/charger plus solar provides the best option for getting close to a full charge from the generator and let the solar top it off the remainder of the day.

ScottG

I'm no battery engineer either, but by studying the change profiles of my small chargers (not to mention charging and maintaining a boatload of batteries) I've noted it's that variation in current (amps) not voltage that determines how quickly your battery will charge.

A high voltage (typically 14.4) is required to "push" charge into the battery, but doing this at a lower flow (current) is generally better for the battery. Small batteries (like those for motorcycles) can even be damaged if charged with too high a current.

A good smart charger regulates both the current and voltage to optimize charging, but will almost always deliver 14.4 in the bulk phase. The WFCO is supposed to have a 14.4V bulk phase as well, but I've never seen it kick in on mine--it usually goes right into float (13.6V). The apparent difficulty in getting the WFCO into bulk mode may be one of the reasons its charge capabilities get criticized, but now we are getting a little out of my pay grade!  :-) 

grubbster

This has me wondering about charging the battery on my 400 when I am boondocking using a generator.  The batteries in these things is neigh on impossible to get to to hook up a charger directly to the terminals.  I have a Victron MPPT 75/15 solar controller hooked up and I was wondering if I could run the battery charger through that since it is wired into the battery and has wires that reach outside the camper.  I have Anderson connectors on the controller wires and it would be easy to take a battery charger and add Anderson connectors to it as well.  Can anyone think of any issues this would cause?  More or less efficient than the WFCO?

ScottG

@grubbster, I don't think I would run a smart charger through a solar controller. I have no idea what would happen or if it would cause any damage, but intuitively it seems like the two electronic brains may not play well with each other.

My inclination would be to purchase or make a dedicated harness for the charger with ring terminals on one end leading a more conveniently located connector to attach directly to the charger on the other. You would still need to get the ring terminals on the battery, but you would only have to do it once.

BrianZ

Agree, @ScottG, or if there are other similar "pigtails" or other wires to be connected to the battery, consider using a bus bar to provide multiple connection terminals which is then connected by just one cable  to the battery.  This removes clutter from the battery & makes the battery easier to service.

klenger

grubbster said:

This has me wondering about charging the battery on my 400 when I am boondocking using a generator.  The batteries in these things is neigh on impossible to get to to hook up a charger directly to the terminals.  I have a Victron MPPT 75/15 solar controller hooked up and I was wondering if I could run the battery charger through that since it is wired into the battery and has wires that reach outside the camper.  I have Anderson connectors on the controller wires and it would be easy to take a battery charger and add Anderson connectors to it as well.  Can anyone think of any issues this would cause?  More or less efficient than the WFCO?

I would suggest purchasing a good 3 stage converter (Progressive Dynamics is one of the good ones) and install it near the WFCO distribution center and connect to the 12 VDC battery bus there.  Next, remove the wire that powers the WFCO internal battery charger from the 120 VAC circuit breaker and cap and stow that wire. Hook up and electrical outlet to the circuit breaker that the WFCO was connected to and use that to power the new converter.  Finally, pull the 40 amp reverse polarity fuse from the WFCO fuse panel and leave it out.  This completely disconnects the WFCO battery charger.  Now when you plug your generator into the trailer 30 amp campground power connector, the generator will power the whole camper, including the new converter and you will be a happy camper.  

If you click on the link in my signature and then select Wiring Diagrams from the top menu, you can view the original 320S and my modified 320S power system.  My system is highly modified, so don't let the complexity of my changes distract you.  Note that the converter I used is a part number specific for the Lithium Ion battery that I installed.  Do NOT use that part number for a conventional battery or it will cook it in short order (constant 14.4 VDC output).