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Old 03-18-2020, 01:32 PM   #1
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New Battery Problem....

So I added four new Trojan T-105 AGM batteries to the toyhauler and a Victron 712 battery monitor before we left on vacation for a month in Death Valley.

I should have 434 AH from the four batteries but we would take 60 or so AH overnight with two cpap's and such - only to wake up with the voltage down to 12.2, give or take. This voltage is way lower than it should be.

I verified the wiring of the battery box - all 2 gauge cable.....I wired them up with the pairs of T-105's in series to get 2 12-volt batteries and then the two 12-volts in parallel. Also tried the bats paralleling two 6 volt batts with a series in the middle. All gave the same voltaqe. Looked at the voltage of each individual battery - all four exactly the same........

Only thing I can now say is bade batteries.

Ideas?
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Old 03-18-2020, 02:10 PM   #2
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Are ALL grounds going to one side of the shunt and ONLY 1 cable from shunt going to both negetive battery posts ?
If not, other loads may not be monitored.

How are you recharging your batteries and do they fully recharge ?
Bulk and absorb above 14 volts and float at 13.5 volts ?

Are you measuring battery voltage with no load on them ?
They need a hour or so to bounce back after being drawn on.
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Old 03-18-2020, 02:27 PM   #3
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according to the Trojan spec sheet 12.2V (6.1/battery) ~ 58% charged

i'll rate the 2 cpap machines @10A - so overnight (10 hrs) you should use 100AH of battery or ~22% of your capacity (no inverter involved)

assuming no other draw on the batteries, you are right, it is lower than it should be, but there are lots of other things using 12V all night

as stated, this is assuming a fully charged battery bank @12.7V at the start of the night

mark
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Old 03-18-2020, 04:32 PM   #4
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Quote:
Originally Posted by Mkaye View Post
according to the Trojan spec sheet 12.2V (6.1/battery) ~ 58% charged

i'll rate the 2 cpap machines @10A - so overnight (10 hrs) you should use 100AH of battery or ~22% of your capacity (no inverter involved)

assuming no other draw on the batteries, you are right, it is lower than it should be, but there are lots of other things using 12V all night

as stated, this is assuming a fully charged battery bank @12.7V at the start of the night

mark
I've checked the cpap draw at around 3.5 A each.

Never had this problem using two T-105 wet cells with one CPAP. Something is wrong.
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Old 03-18-2020, 04:36 PM   #5
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Quote:
Originally Posted by twinboat View Post
Are ALL grounds going to one side of the shunt and ONLY 1 cable from shunt going to both negetive battery posts ?
If not, other loads may not be monitored.

How are you recharging your batteries and do they fully recharge ?
Bulk and absorb above 14 volts and float at 13.5 volts ?

Are you measuring battery voltage with no load on them ?
They need a hour or so to bounce back after being drawn on.
Neg batt cable hooked up per your example.
I drove from Portland to Death Valley over two days with 10 AMP charge from truck. I've used on board generator with 60 amp converter/charger to 95% per Victron and Also have 320 watts of solar. I should be filling them up.....
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Old 03-18-2020, 05:01 PM   #6
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I'm going to get to a full charge via the Victron tonight and then disconnect the positive cable from the busbar. I'll take a voltage reading in the am to arrive at a resting voltage reading.

The tech at Trojan says the resting voltage should be 12.84 volts.

More news in the AM!
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Old 03-18-2020, 05:02 PM   #7
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If you tested the voltage on each battery, while disconnected from the others, and they test the same, it would mean all 4 are bad. That just seems unlikely.

I would seperate them and let them sit a day or so and see if one or more drop in voltage, indicating a bad one.
If your traveling, just run on 2 batteries a day or so and then the other pair to see if one set has a problem battery.

Are you sure all 4 are batteries are wired in.
Click image for larger version

Name:	6v-battery-series-and-parallel-wiring-600x519.jpeg
Views:	10
Size:	35.5 KB
ID:	278406
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Old 03-18-2020, 05:24 PM   #8
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Originally Posted by twinboat View Post
Are you measuring battery voltage with no load on them ? They need a hour or so to bounce back after being drawn on.
This is very important, and I would say a minimum of 3 hours of no load. Industry standard is 24 hours of rest. Battery temperature will influence the voltage as well. Temperature correction factor is published on the data sheet.

How many times have the batteries been cycled? It takes a few cycles to "break in" new batteries. I've seen new batteries only come in at around 50-70% of rated capacity for the first few cycles.

Your battery monitor will tell you how many Ah have been drawn and give you an estimated percentage based on pack size at that draw. To estimate capacity based on terminal voltage alone of an actively used pack is difficult and inaccurate at best. If you really want to know a hard number, do a measured capacity test at the 20 hour rate.

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Old 03-19-2020, 05:19 PM   #9
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Quote:
Originally Posted by twinboat View Post
If you tested the voltage on each battery, while disconnected from the others, and they test the same, it would mean all 4 are bad. That just seems unlikely.

I would seperate them and let them sit a day or so and see if one or more drop in voltage, indicating a bad one.
If your traveling, just run on 2 batteries a day or so and then the other pair to see if one set has a problem battery.

Are you sure all 4 are batteries are wired in.
Attachment 278406
This is the way the batteries are wired.
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Old 03-19-2020, 05:33 PM   #10
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Originally Posted by Mark_K5LXP View Post
This is very important, and I would say a minimum of 3 hours of no load. Industry standard is 24 hours of rest. Battery temperature will influence the voltage as well. Temperature correction factor is published on the data sheet.

How many times have the batteries been cycled? It takes a few cycles to "break in" new batteries. I've seen new batteries only come in at around 50-70% of rated capacity for the first few cycles.

Your battery monitor will tell you how many Ah have been drawn and give you an estimated percentage based on pack size at that draw. To estimate capacity based on terminal voltage alone of an actively used pack is difficult and inaccurate at best. If you really want to know a hard number, do a measured capacity test at the 20 hour rate.

Mark B.
Albuquerque, NM
I disconnected the batteries from load after a full charge last night per the battery monitor for about 18-hours. The resting voltage was 12.87 this afternoon. Trojan said it should be 12.84 after 12-hours so we are ok there.

I've cycled these guys like 30-times over a month in Death Valley. I did not see any improvement in performance.

A couple of the nuts on the bus bar were not tightened down firmly, I've corrected that and will check voltage with no extra load tomorrow. I'm not an electric guy, would semi-loose bus bar connections cause issues?

If voltage is ok tomorrow am, we'll then sleep in the trailer with both cpaps going to replicate the environment we had while on vacation.

Mark - I undersatand just using voltage to assess SOC is a crude sword, but the voltage shouldn't go down to 12.15 after drawing out only 65 or 70 AH.....

I guess after that a load test.
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Old 03-20-2020, 08:30 AM   #11
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Quote:
Originally Posted by Oregon RR View Post
I disconnected the batteries from load ..The resting voltage was 12.87 this afternoon.
Good.

Quote:
I've cycled these guys like 30-times over a month
OK, check that box.

Quote:
A couple of the nuts on the bus bar were not tightened down firmly,...would semi-loose bus bar connections cause issues?
Loose connections are more resistive and will cause voltage to go down under load. I wouldn't expect the voltage to change any with no load so a static measurement after fixing it won't tell you much.

Quote:
we'll then sleep in the trailer with both cpaps going to replicate the environment we had while on vacation.
Or any equivalent load, unless you don't mind spending the evening out there proving the point. Is your battery monitor connected directly to the battery or at some other point in the system? If it's not right on the battery then any voltage drop through wiring and connections will influence your measurement. A measurement under load right at the battery with a 2nd meter to see if they agree would be a useful data point.

Quote:
the voltage shouldn't go down to 12.15 after drawing out only 65 or 70 AH.....
But you're assuming that the 12.15V you're seeing is a hard number for SOC, and we're saying that terminal voltage except for a very specific conditions won't be accurate. Between "loose" connections and unknown measurement conditions I would put that 12.15V reading as suspect and would chase down a more accurate means of measurement. The most direct and quantitative answer would be a load test at the 20 hour rate. Anything you'd do using loads in the coach is kind of "squishy" due to losses in the system and load dynamics. A 20 hour load applied directly to the batteries isolates those variables and provides a hard number. This assumes proper charge profiles are used which is another issue to explore. All this isn't to say your observation is without merit but there are a number of installation variables that affect capacity directly that have to be ruled out before declaring it's the fault of the batteries.

Mark B.
Albuquerque, NM
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