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Did I speak with forked tongue? Chassis voltage.


Smitty77_7

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A gent in the park we're in, walked over with his multi-meter and asked my opinion on the voltage he'd read on his coaches chassis battery. 

He read 12.48, with his house battery charger (MS2012, with the Smart Battery Combiner) having been off for over four hours. Single wet cell 8D Chassis Battery. (I have the MS2812 with the SBC, so familiar with it.). 

I first asked him if he'd observed the LED lights of the SBC before turning the Charger portion off. He said he had not. I then asked if he'd turned of the Main Battery Disconnect, rear main unit, not the in the door Salesman Switch - and he said he had not (Actually, he said he did not know he had one.) 

So I told him that his Chassis Battery was still supporting some minor loads (Radio, Onstar, LP Detector, ECM's, etc. And that I felt 12.48 range was fine. Maybe not full charged, but pretty dang close. I said I'd be surprised that if he were to either turn of the Main Battery Disconnect, or even better, disconnect the cables to the battery itself, and let sit for a few hours, he'd probably see the reading higher then the 12.48 he'd just measured. 

I also suggested he could turn his charger back on, let it sit for a bit, and then go look at the LED status of the SBC. Suspected he'd see that it was Status of Solid Green, and the Disconnected LED would be off - indicating both House and Chassis were fully charged. That if he'd monitor the SBC LED's for the next few days, he should catch the Status & Disconnected LED cycling thru different levels of charge maintenance. 

He said he was told by his FIL, that he should see a Greater Then 12.6V reading at the chassis. So was concerned his chassis was not doing well. 

Again suggested he disconnect the cable from the battery, let it rest, and then take another multi meter reading. And that IMO, 12.5 to 12.6V reading would be fine. (And again, to turn on the Magnum Charger, and monitor the SBC LED's - as I suspected he'd see the SBC felt the Chassis was fully charged, even with a 'moderate draw' of power reading of 12.48. And to stop at NAPA or Autozone and get a good quality tester and suck some juice up and get a reading to compare to the his multi meter.

He's here for another two days, and if I've 'spoke with forked tongue' and given him bad info - be happy to go correct my thoughts. (Heck, I just stepped out and did a multi meter reading of my 8D chassis battery (Wet Maintenance Free 4 1/2 year old CAT battery.), and had a reading of 12.45V. My SBC Meter reflected Solid Green Status, and no Disconnect led on at all - so it feels all of the batteries are topped off fine...). I think, this reinforces my feedback to him. And looking at some reading I took back in January (Had blown a fuse on the SBC, so was monitoring things after replacing the fuse.), I had readings over four days of 12.45 - 12.58V under the same conditions. 12.97 - 13.0V when the SBC indicated it was charging the Chassis. 

Sure, long winded again - but hate to pass on bad info to a newer RV'er. So if I did, want to correct it before he heads on:)!

TIA for Monday AM Quarterbacking for me,

Smitty

 

Be safe, have fun,

Smitty

04 CC Allure "RooII" - Our "E" ride for life!

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Smitty, here's a state of charge versus voltage chart for flooded lead acid batteries at rest at 77 degrees:

Temperature: 77 degrees Fahrenheit

 Percent  Hydrometer  Unloaded
  charge     reading   voltage
     100       1.265     12.63
      75        1.210     12.30
      50        1.160     12.00
      25        1.120     11.76
       0         1.100     11.64

As you well noted THATS AT REST AND STABILIZED. Of course, as you already are aware if there's a load AND SUBJECT TO HOW MANY AMPS  Id naturally expect the voltages above to draw down WELL DUH. Its been my experience different brands of so called "Smart" chargers have different charging algorithms.

2 hours ago, Smitty77_7 said:

He said he was told by his FIL, that he should see a Greater Then 12.6V reading at the chassis

The FIL is correct PROVIDED THAT the batteries are under charge (then maybe 13 to 14+)  but as you know NOT if there's no charger running and loads are drawing current.

I agree a good quality load test goes a long way.

Best wishes

John T    PS finally, law work done, home inspections and appraisal,  headed out in the RV tomorrow for Wisconsin, Minnesota, Iowa (Ferguson Expo) and Illinois (Half Century of Progress Antique Machinery Show) yayyyyyyyyyyyy

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For what it is worth.....Here is another possible scenario to low voltage readings with a MS2012(or any Magnum inverter) equipped with the BTS option.....

 

I had similar readings on my coach(which has a MS2012 with 4 Group 27 12volt batteries) last summer and after my local RV repair guy talked to his regional rep for Sensata (Magnum's parent company) he suggested checking the battery temperature reading on the remote. It read 99celsius, seemed odd that the batteries were at 4times the ambient air temperature that day but were cold(relative term) to the touch. It turned out that the Battery Temperature Sensor(BTS) for the inverter had crapped out and was telling the inverter the batteries were at 99degrees Celsius and therefore it cut the maximum charge voltage to ~12.5volts. Immediately after unplugging the BTS from the inverter the voltage increased to well over 13volts. Replaced BTS and no more low voltage.

 

 

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I talked with my neighbor before they pulled out. He updated me that yesterday afternoon he had:

-Observed that the SBC Status Light was solid Green, no other lights, indicating fully charged batteries based upon the SBC settings.

-He had disconnected the ground from the chassis battery terminal, and just under four hours later, had a reading of 12.56V from his multi-meter.

He still felt that was a bit low, but was pleased to see it raise from the values he'd read while under slight load. 

I suggested he do some monitoring of his House Batteries, and then check the setting on his Magnum. (It was programmed by the RV Tech that installed his battery, Magnum, and related Magnum components.). Pointed out that the combo between MS2xxx & SBC would not shift power to the Chassis - until the parameters that were programmed for the house were met. 

Good chance he is fine, maybe a bit on the low side on the Chassis. More monitoring of the Chassis battery would also be prudent... But coming back up some without load, is a positive. (Seems I recall that 6-8 hours of resting after load/charging, is better then under four hours?). 

He also told me that he had found the Battery Side of Life 1 & 2, that I had referred him to the first day. Has them saved, as well as he'd done lot's more surfing on battery management in general. 

Made me chuckle, as he said he felt a bit foolish for not knowing some of this already. I laughed a bit, and told him about every 3 to 4 months - I seem to learn what I thought I knew about batteries, our Magnum systems and components, our solar and MidNite Classic Controller, etc. - was in need of 'adjustment'... That it's all part of the RV'ing experience. And sure, sometimes the lessons are expensive (Two times I had less then 3 years on chassis battery of a previous coach. (Good quality batteries.) Until somewhere I read to also check where the ground attacks to the frame... So $$ lessons are OK, as long as you learn from them:)!

Thanks again for the sanity test, best to all,

Smitty

Be safe, have fun,

Smitty

04 CC Allure "RooII" - Our "E" ride for life!

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Received an email from the gent this morning, as he has moved on from the park we're in. 

When he got to the new park, he went thru normal set up including Shore Power, and his Charger kicked in, did not remain on too long, as the house was at 100% SOC, went into float mode reflecting 13.1V by his BMK Meter and also by his multi meter at the battery an the SBC too. 

SBC reflected the same Green Status light, indicating both batteries were seen, and no need to divert to the chassis (That is how I interpret the manual on the Status of solid green.) Connect and Low/High Disconnect are at Magnum's default settings. 

He said he then drew a draw off of the chassis battery for several hours, lights, radio, and hooked up an air compressor with hose clamps to the chassis battery, and was very popular as he'd run it for 10 mins, then off, then 10 mins, more - etc. 

He exercised the chassis battery downwards, for about three hours. Turned off everything, except for the earlier posts mention of parasitic draw down from the chassis (ECM's, Radio Memory, LP Detector, others(?). He waited 90 mins, then took a reading at the chassis battery with his multi meter. And a reading of 12.29V. He and I both felt, and house still showing 13.1V in Float Status. 

He and I both felt that the SBC should have shifted power over to chassis battery? But same solid green Status light is on. 

He said today he was going to a NAPA to purchase a hydrometer, and will pop his MF cap off and take a reading, to compare to the multi meters. 

I suggested he also send a request to Magnum for a Tech Support gent/lady to call him back, to review what he was seeing. (Get in line, as they can sometimes get some back up:)!). 

Any other thoughts on this, and I'll send them to him. (Invited him to join the Forum, even as a non Escapee member, and he does not seem to want to do that...).

Very possible what I thought I understood about the SBC functionality, is faulty:)!

Best to all,

Smitty

 

 

Be safe, have fun,

Smitty

04 CC Allure "RooII" - Our "E" ride for life!

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So, this should be the final post - having fun with my own updates:)!

He did talk with Magnum, and they had him go recheck the Auxiliary/Chassis Blade Fuse again. Asked him to remove it, and put in another one. He did, and all is working as it should now... They recommended he buy the fuses that have light that goes on when blown, and the same thing they told me about 18 months ago - to move up to a 30A from 25A fuse. (Seems his installer also used the 25A that came with it, but for the kind of install he has (And me too...) 30A is more appropriate. 

He explained that once the chassis batter dropped low enough, he would no longer see a Green Status light. It would turn to Red for Fault. Which is what I had with my coach 18 months ago. That he agreed it was a bit misleading that the Status Light remains Solid Green even with a blown fuse to the Auxiliary/Chassis battery (Chassis in our RV install, for boats, it could be a generator battery, starter battery, etc.). 

So, I've updated my own notes to always check, and remove and test, my Auxiliary/Chassis blade fuse whenever I'm seeing 'unusual' voltage readings... 

Hopefully this will not be an ongoing problem for him, after going to 30A. In four or so years, I've had this happen only three times... 

Best to all,

Smitty

 

 

 

 

Be safe, have fun,

Smitty

04 CC Allure "RooII" - Our "E" ride for life!

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