Charging a Battery Bank

[RobWNY]

I am planning on upgrading my batteries to 4 6v batteries wired in series and parallel to have a 12v system with plenty of Amp Hours. There is a ton of information on how to wire things up but nothing on how to charge them both to top them off while boondocking and long term during the winter month's. Do I have to disconnect the parallel connection and charge them as 2 separate 12v banks (2 banks of 2 6v in series) or unhook everything and charge as 4 independent batteries or is there a charger that can charge all 4 batteries without disconnecting any of the battery connections? Also, what would be a good battery charger to get to accomplish the charging? I have an inverter generator and I'm looking at portable solar panels in the future to use while camping and will be storing the batteries in my basement during the winter month's. Thanks for your input.

[landyacht318]

Auto parts store cables use steel ring terminals and are junk. Your series cable is one such cable.

[Joel_T]

[MEXICOWANDERER]

Troubleshooting flooded battery problems without using a hydrometer as a polygraph versus instrumentation is like trying to drive blindfolded wearing ear plugs. Post an image of your shunt and exactly how it is connected please 🙂

[BFL13]

That is a good set-up for the camper, with the solar, inverters, converters, monitors, etc.

In the photo it is not clear where the PM-75's chassis ground goes. It is supposed to go to the rig's frame independently. The input 120v cord's green wire goes on the chassis inside and the chassis external 'ground lug' connects to the rig's frame. AFAIK it is for reducing noise on radio and TV. The converter works ok without it.

I am not sure what can go wrong if the converter's chassis ground gets mixed in with the output neg DC down the line somewhere on the way to the frame. It is a big no-no to bring an inverter's chassis ground around to its DC neg input, and get to the frame via the battery neg to frame.

[Joel_T]

Oh, there's no rush in my blood to go buy new batteries. Other than they aren't acting like everyone thinks they should I've no solid evidence, yet, that they're on their deathbed. I'm gonna keep an eye on them and let things settle for a bit. Nothing about my batteries, or charging, has followed conventional wisdom or preconceived notions. In a bit, if they're drawn to 50% SOC from lack of a mix of solar or shore power, I'll try the PM again. If I get itchy I'll try the invertor load on the batteries and see what the PM does.

[BFL13]

The batteries don't have to be perfect to still do the job. No panic to rush out and replace just yet.

A newbie guy with a used trailer, I was helping had two old 6s (Interstate/USB U-2200s) and was running his microwave etc with a 3000w inverter from those two batts no problem.

I checked his SGs and one of the 6s had SG in the red on one cell and two in the green, while the other 6 had two cells in the red and one in the green, best they could get to on a proper recharge. Still worked! I was amazed to say the least.

I sold him my spare 130w panel and got that set up for him, and he went for two more months like that till end of that summer camping season, and got away with it.

I told him to wait till Spring before buying new batts. He then got four new 6s for the new season and is now starting his third year on the new batts.

So there you go.

Meanwhile, I hope you found whatever was the problem with the 75 not charging after you re-installed it.

[Joel_T]

I cheated on the charger wiring...I'm cheap and lazy sometimes. The 2 red wires were cut from one wire that had lugs on both ends. Not proper I know. The controller, inverter and charger leads all go to the same posts. The drawing separated them a bit for ease of drawing and understanding. One of the bigger puzzlements to me is, based on SG, how I got from 0% SOC to 100% in 2 hours. That cabled charger is an old Harbor Freight CenTech garage unit that has a timer and can be set on 2a, 10a, 40a or 200a for starting. Nothing special. I'd originally been happy (will still be) if the PM could get from 50% SOC to 80 or 90% SOC in close to 2 hours.

I need to "unpack" the batts to watch SG before more testing. Both low cells were in the same battery...didn't notice seeing different levels but will check.

[BFL13]

LY that is the new PowerMax with a hole in the side so you can get at the little pot inside with a small screwdriver like for eyeglass frames. (Second hole is for a switch that changes it from 3 or 1 stage, which is adjustable voltage for that one stage)

Idea is you can use it as a regular 3 stage or as an ADJ as required--very nifty concept, but a little awkward to operate without being right up to it. It only comes with the external knob and voltmeter if you special order that, or just buy the older model with those.

I can't tell from the photo what is what for checking things. Seems he used two red wires from the terminals (ran out of white?) but hard to match the photo to the earlier schematic.

Anyway, OP- with solar and WFCO turned off -just turn on the PM-75 (see the green light is on!) and use the meter to check for voltages starting right on the unit's two terminals, and then at each junction along the way to the batteries looking for the break in the path either on the neg or pos path or both.

Be too easy if it is just no 120v input--no green light--to fix that.

[landyacht318]

The 2 hours of a garage charger What is make model? got a link/photo? raising SG from flat to near full levels would seem to indicate severe stratification. the hydrometer was pulling much less dense acid from cell tops. The garage charger's amperage and its near 16 volts caused enough gassing and perhaps heating that mixed up the electrolyte so it appears that the battery went from near dead to near fully charged in 2 hours, which is impossible unless they are severely capacity compromised.

Your powermax adjustable voltage model, should have been easily able to outperform the garage charger, but I do not see a voltage adjustment potentiometer in your photo. The adjustable voltage model I am familair with has a small voltmeter on the top, next to the potentiometer.
Without it perhaps the 3 or 4 stage automatic unit saw 13.6v from other charging sources and decided to do nothing.

If it was an adjustable voltage model working properly it would seek to bring voltage at output terminals to what it was set at, with its maximum available amperage until that voltage was reached.

it looks to me, from your photo, that you have an automatic 3 or 4 stage powermax, and I do not think these make for a great converter for fast and complete battery charging in a timely manner. I'd only ever consider their adjustable voltage manual models as I do not like their automatic charge algorithms, and would choose a PD92XX-14.8v series converter instead, if I wanted a converter, which I do not.
At least that model through pendant/wizard allows for a manual voltage override.

I take care of several neighbor's batteries on occassion. they usually have these ridiculous chargers on them for 12 hours and expect them to be fully charged. the biggest joke of them is a 12/2 amp manual transformer based Schumacher charger that cannot exceed 4.2 amps and 13.74 volts. What a joke of a charger.

I frequently find SG deep down in the red despite an overnight recharge on the well marketed garage charger, and no longer try and get their chargers to do anything, I instead take out my Meanwell rsp-500-15, set to to 14.8 ish volts and let it go until amps taper to ~1.5% of capacity, dip the hydrometer, and then possibly crank voltage up to as high as 16.2v, if required. No worrying about if it is going to charge or not.

It is single minded in its pursuit of the target voltage I chose before hooking it to the battery, or afterwards, once amps taper and there is little voltage drop on the 8awg DC output.

Nothing worse than a charging source deciding upon a timid target voltage when the batteries are anything but fully charged, or one charging source has still depleted batteries at a high enough voltage that the other charging source decides it does not have to do anything.

Why your powermax did nothing needs to be investigated but other charging sources or surface charge from recently applied charging sources, having battery voltage above 12.8v are the usual culprit.

The two cells which read 1.265, are their electrolyte levels a bit higher than the 1.275 cells? The low cells in the same GC-2?

[Joel_T]

Here's a picture. Kind of awkward but I think all the connections are obvious. The furthest post switch to 2/0 is positive. There's a fused disconnect like the Morningstars not quite visable for the battery side of the controller. After a lottery win the Centech is to be replaced by a 2000w puresine. I'd like to know if there's something wrong here.

[Joel_T]

I'll get a couple pics of the setup in the pass through later this am. The charger's hung upside down on the roof of the pass through with the holes facing the door. I've clipped some tester leads to the feed going to the batts so I can always check voltage right there.

The shunt's directly hooked to one of the batteries neg post with a 3" piece of flattened brass tubing with holes drilled in both ends for the post and shunt. It's my understanding that that is as good as it can get. There was definitely something screwy for a 50% reading to be in place of a real 0% SOC. I think it was a recent fluke as the percentage readings to my knowledge have kept pace with actual amp usage. It's a pain to "unpack" the batteries for a SG check but I will be frequently comparing Trimetrics %SOC with SG for a bit.

[BFL13]

It is a puzzle why the 75 did nothing after being reinstalled. It did have DC output in its bench test before that. No doubt the OP is chasing that down with a multimeter.

Once this all gets sorted out, I would like to see (photo please) how the PM-75 is installed so you can get at it to operate the voltage adjustment pot and see the voltage changes as you do that.

Just getting at the hole to put in the small size screw driver is one challenge. Running back and forth to see the Trimetric display is another. A voltmeter co-located with the adjustable converter solves that. If you can easily see the voltmeter while twiddling the pot!

It is easy to arrange for all that in some RVs and not so easy in others, depending on physical layouts. The OP could demonstrate how he does it, which would help others. With adjustable voltage converters becoming the new thing, we are all going to have to solve that somehow.

[westend]

Joel,
If you are relying on the Trimetric for measuring, I'd suggest to locate the shunt at the frame ground with nothing between the shunt and ground. Your diagram does not illustrate this location and may be the cause of the inaccurate measurements.

[landyacht318]

I would prefer the charging source hold 14.7ish volts until amps taper to 1% of capacity before initiating any EQ voltages . If that happens then A healthy battery should not require more than 5% In amps, of battery capcacity, 5 amps per 100Ah of capacity, to be brought to 16 volts, or 16.2v as trojan an Rolls Surrette now prescribe as an EQ voltage( at 77f battery temperature).

Important thing is his charger got Sg to respond on most of the cells. See if those last two can catch up, then see how the batteries handle a normal overnight usage

I still EQ charge the screwy 31( group 31 marine USbattery) once in a while, originally rated at 130Ah capacity. 5% of 130 is 6.5. Usually it took only 6.2 amps for it to achieve 16 volts, and I'd hold 16v until it reached 1.280 on all cells or until they no longer rose, or amps started increasing to maintain that 16v.

Battery temperature played a big part in how long it took to max out SG. Hot days it happened faster, in my observations of that specific battery.

When one of its cells refused to respond to EQ voltages, I also noted that cell got hot on the bottom and removed it from deep cycle duty. I expected it to short out well over a year ago, but the battery keeps delivering shallow cycles without issue, and will maintain 12.79v when unloaded for 4 days after a full charge.

Max out the SG, test it. Perhaps test it to well below 50% state of charge then max out SG again on whatever charging source can accomplish this. Perhaps it will like it and restore some capacity. perhaps not.

If not, you now know how to keep the new batteries performing well. Get that SG up, pronto, and keep it there until it is time to work the batteries again.