Balancing battery bank charging

[Life-in-Him]

Question re charging of s battety bank.

Have 2 grp 27wetcell batteries in parallel.

From DC theory years ago, we learned that even a small resistance value, like inter device cables, would cause a difference in charge-discharge amounts. Thus a best scenario would be to parallel in the middle junction or use a reference tag from the far end back to a smart charger.

Our batteries parallel from the end.

We used the midconnect process in huge (100-500kw) banks years ago.



Has anybody tried or seen a difference using mid connections of parallel bank on RV's

[chuckster57]

I have always hooked the trailer leads to opposite ends of the bank. I personally doubt anybody on this forum has taken the time to test the differences.

For true accurate results, wouldn’t you need the same conditions for both scenarios? Likely not to happen with weather changes, etc.

[Life-in-Him]

Opposite ends makes sense.

The delta voltage drop would average out especially on the charge cycle.

Ours are on the same end & I've noticed if we have a dc discharge (power outage :35 min last Friday before generator came on) of just the basics (controllers only, no hi loads) we're still running 13.8v.
It'll take 3-4 days to come down to float @ 13.2v.


I've checked each battery voltage off line & it's 12.7 or so last time after we get to 13.2.


Seems like a long time to flatten out with only 1-4A drain.

[Life-in-Him]

Finaly dropped to 13.2 this evening.

We're going to do a load test tomorrow.

Interesting thing, the tank sensors are correct now.

[JRTJH]

There's a very good "theory of operation" document located on the WFCO website that explains how their converter/chargers work, what "triggers the changes between charging modes" and how the "voltage/current relationship" is maintained....

Essentially, we are all "trained to monitor voltage" (voltage regulation systems) where the WFCO systems are not "voltage regulated" rather they are "current regulated" and voltage will vary to maintain a consistent "current charge" to the battery bank.

You can download the WFCO Theory of Operation document here: https://wfcoelectronics.com/wp-conte...eration-v2.pdf

While it's not an "easy read" that document, along with the information in the WFCO Owner's manual will give you a better understanding of the relationship to regulating the battery charging (both time limited and voltage limited). You'll also find an "interesting tid-bit" hidden in the text: The converter will only "enter the float mode" (13.2 VDC) if there is no "current demand on the system for 44 hours"... In other words, turn on the water pump, open the refrigerator door (interior light comes on) or even turn on the overhead lights in the trailer, and the "44 hour clock" resets and the timer begins all over at zero. So, theoretically, many (maybe most) people will never see their trailer converter/charger output read less than 13.6 VDC, even with the RV in storage, because as soon as they open the trailer door and turn on the overhead lights to better see the power center door, they have "triggered float mode disruption"...

With a "1-4 amp drain", in theory, the WFCO micro-processor would never allow the converter/charger to enter the float mode.

[chuckster57]

John, I’m glad your really retired and can spend time reading for me. How much do I owe you

Good info to know, RVIA training is fairly basic.

[JRTJH]

Originally Posted by chuckster57

John, I’m glad your really retired and can spend time reading for me. How much do I owe you

Good info to know, RVIA training is fairly basic.

I can't remember the "why" that led me to that document, but after I found it (hiding in plain sight) and compared the information in it to the information in the WFCO Owner's Manual, that "theory of operation" filled in much of the "left out info" in the Owner's Manual. Filling in the blanks helped me understand some of the "WFCO WTF moments" when my voltmeter didn't read what my intuition thought it should read"....

Essentially, at least for me, realizing that current regulation is the way WFCO monitors and charges batteries was the key.... My "feeble mind" kept going to the "basics of voltage regulation" not "current regulation" (voltage and current are "inversely proportional" and when voltage increases, current decreases in a regulated circuit)...

Once I started thinking in those terms, it made sense to me that even though the voltage output is only reading 12.7 VDC at the converter terminal (when connected to a battery bank) it can still be "bulk charging the battery" at 30 amps. Doing the "math", 12.7 VDC @ 30 amps is the same 371 watts as 13.6VDC @ 28 amps.

It's the same with AC voltage as well. 105 VAC @ 15 amps is 1575 watts while 125 VAC @ 15 amps is 1875 watts.... While it might seem "insignificant", a "brownout condition" where the trailer Air Conditioner requires 1800 watts to operate, it is drawing 15 amps on 120 volts... At 95 volts, that same Air Conditioner will be drawing 19 amps... Just under the 20 amp circuit breaker, so the compressor "overheats and burns up" without tripping the 20 amp breaker.... (that's why an EMS is so important)

The same "principle applies to battery charging" and explains why sometimes you'll see 12.7 VDC on the battery terminals and the battery is still charging and not "overcharging"....

I know, I know: "Clear as mud"....

[chuckster57]

Perfectly clear !! Thanks

[Life-in-Him]

Thanks JR
Constant Current Reg. (CCR) & the 44 hour timer were the missing parts.

CCR is not a difficult thing to understand. It was just missing from my brain since it looked like the system was doing voltage regulation. 13.8V, 13.6V, 13.2-13.3V.
However so far it doesn't look like the 44hr timer follows the rules.

I'll keep trying to connect to WFCO doc site.

After the 44hr timer starts Float mode, there must be a mini/max current draw that passes another time to be in maxV-minI mode

I haven't been able to connect to the WFCO site but the

[JRTJH]

If the previous link won't work, click on https://wfcoelectronics.com/ then click on SOLUTIONS, then "Theory of Operation" Maybe that will work ???

[flybouy]

Originally Posted by Life-in-Him

Question re charging of s battety bank.

Have 2 grp 27wetcell batteries in parallel.

From DC theory years ago, we learned that even a small resistance value, like inter device cables, would cause a difference in charge-discharge amounts. Thus a best scenario would be to parallel in the middle junction or use a reference tag from the far end back to a smart charger.

Our batteries parallel from the end.

We used the midconnect process in huge (100-500kw) banks years ago.



Has anybody tried or seen a difference using mid connections of parallel bank on RV's

What may make great sense in theory may not make as much sense in a real world pratical application. This, combined with the scale difference would make the change negligable. A 1/2% increase in 500 KW would be a 25,000 difference. Scale that down to 2 12 v batteries and the gain wouldn't be worth the extra cable, and connections that would be potential areas for corrosion and connetion issues in a moving, vibration prone open air environment. JMHO

[Life-in-Him]

Finally got onto WFCO's site & followed the links to the "how it works" pages.

They are switching power supply technology which makes the current regulation straight forward.

The 4 hr. /44 hr. Timer area says that can do a lot to recover deep discharge event damage.



We did a load test of the batteries today. Operating voltage was 13.2.
Didn't wait for voltage stability (usually 30 min)

High load (30 amps) was held on for 5 min.
Va dropped to 12.7v under load & came back up to 12.8 in about a min under no load.
Digital vom read the same as incommand before & after tests.

System reads 13.8V 2 hrs later.



Essential our batteries are both good & not noticeably damaged by the -25° F they endured last Dec for 2 weeks.

They were fully charged before hitting the welcome to Tx, Ok, panhandles & eastern Co.



They are G24,CCA 550, MAC @32 675, 23 Max @ 32 - 140 min (2-2020 & 3-2020

Not great but that's what we have.

Can't $$$ anything bigger or better till something dies.


Did find one doc saying connect @ opposite ends to get good balance which is where we started this.



Thanks for the info.