Diagnose extreme DC capacity loss when no AC

[JRF0st3r]

Our '67 Safari has all new electrical which I installed. We had kept it plugged into shore power and stayed at full hook up campgrounds until we stopped at a motel on our return from Galveston. Power cord to truck was unplugged. Next morning battery capacity was at 25%. The only appliance running was our AC/DC Isotherm DR 65 refrigerator which should on average consume 30 amps per 24 hours.

Our DC system includes 2 12 Volt AGM Lifeline (GPL-31XT) 125 amp hour batteries, Progressive Dynamics Intel Power 9200 Power Converter (PD9245C) and Bogart Engineering's Tri-Metric Battery Monitor 2030. All of this plus our refrigerator seemed to work hunkey-dorey until we "boon-docked".

With the refrigerator running with only DC power on the Tri-Metric registers -45 to 55 amps immediately. Plug in the AC and Tri-Metric shows + 70 to 80 amps. I pulled out the refrigerator to measure its amps it was using with only DC and it showed about 3 amps, about right for the Danfoss/SeCOP BD35 compressor since I left the drawer open for a minute or two. Then I disconnected the refrigerator and the Tri-Metric went back to normal, around + 0.2 amps.

I also discovered that driving back with the power cord connected to the truck battery capacity remained as low as when first discovered but did not lose more. Should the truck have recharged the trailer batteries?

What is going on???

Jim

[uncle_bob]

Hi

If your load pulls 50A and you have 250AH batteries, they will be dead flat in under 5 hours. (Capacity at C/5 discharge is < 250AH). They will be at the "this will damage them" level in under 2.5 hours. A 12V 30A load is sustainable for about 4 hours before you risk damage to the AGM's.

Bob

[JMynes]

Originally Posted by JRF0st3r

I pulled out the refrigerator to measure its amps it was using with only DC and it showed about 3 amps
Jim

I suspect those 3 amps you measured were 120v AC coming out of the inverter.
If you had measured 12v DC amps going from the battery to the inverter you would have seen much more.
Amps x Volts = Watts
My current RV fridge is 440 watts. previous RV fridge was 400 watts, I rigged it to run on the inverter and it drew 35 watts from the battery, but the motor home had a 175 amp alternator that kept up just fine.

[HiHoAgRV]

See if the trimetric is programmed for the wrong shunt size. 55 amp draw is HUGE! They offer 2 different shunts, it might be calculating the draw for a high amp shunt when actually you have a low current one in the system.

[uncle_bob]

Hi

50 A at 12V into the inverter is not a crazy number. That's only 600W into the 1KW inverter. If it's 80% efficient (which could be optimistic) you have about 500W on the inverter output. Indeed it's a bit crazy relative to the batteries. The whole system is a a bit of a compromise between multiple objectives.

Bob

[JRF0st3r]

Guys,
Thanks for sharing your ideas! I have no inverter so that is not the issue. At this point I think the TriMetric system may be the problem.
Jim

[uncle_bob]

Hi

Check the idling voltage on the batteries with a multimeter. If they are sitting down around 12.0 to 12.2V, they are indeed discharged.

Bob

[HiHoAgRV]

If you have the user instructions for the trimetric, you can check the shunt program pretty easily. If P7 is NOT set to L3, then by default itsooking for a 500A shunt. All of the ones I've installed shipped with a 100A shunt, thus the problem.

If you set P7 to L3, then you can change P11 to Sh.L, the proper setting for a 100A shunt.

On edit, I'm sure your unit is looking for a 500a shunt since the display has only 1 decimal. XX.X amps. When set for a 100A shunt, it shows XX.XX amps, with 2 decimal resolution.

[JRF0st3r]

Very helpful replies!
Thanks
Jim

[trumpetguy]

My fridge pulls 40 amps on inverter. That's from the Magnum remote plus the Blue Sky remote.

[HiHoAgRV]

Drawer DR 65 Stainless Steel Refrigerator / Freezer
Compressor: Built-in Danfoss BD35F
Voltage: 12 / 24 Volt DC and 100 - 240 Volt AC
Current Draw:
Compressor Running: 5.0 Amp @ 12 Volt DC (half at 24 Volt DC)
Average: 0.9 Amp @ 12 Volt DC *

We have a different animal here

[JRF0st3r]

HiHoAgRV, you are correct on several fronts. Our Dr 65 Frost Free should average 320 watts in 24 hours so perhaps 25 to 30 amp hours?

I ran another test today and found that the battery voltage was at 13 when the TriMetric showed 85% full. When compressor was running voltage dropped to 12.8 V and the reading was the same on monitor and with a multimeter at the battery.

Responding to your suggestions I verified that "Charged" level had been set at 14V and battery capacity was at 250 amp hours. The problem (thank you HiHoAgRV) was that the shunt type was set at the factory at 500 A but I had installed a 100 A type. I have been using Operating Level 1 for which the shunt type is fixed at 500 A. The Instruction Manual says "if your “amps” readings appear to be off by a factor of 10, the most likely cause is this is not set correctly for your shunt.” I then tried to change Operating Level so I could revise the shunt type but the darn TriMetric would not allow me to go above Level 1.

One of the sharpest minds for this stuff is Lew Farber aka "Lewster" and he was a big help is solving the problem. Perhaps I could figure out how to live with the TriMetric but, taking Lew's recommendation, I have ordered a Vilctron BMV-702 to replace it.

Thanks again to all who responded!

Jim