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Old 08-06-2017, 06:17 PM   #531
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I would assume that a sophisticated system such as the RT one has some kind of shunt based battery monitor to let user know SOC level. As indicated on the previous post chart this type of battery monitor is critical for Li batteries, voltage measurement is practically useless.
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Old 08-06-2017, 06:28 PM   #532
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I would assume that a sophisticated system such as the RT one has some kind of shunt based battery monitor to let user know SOC level. As indicated on your chart this type of battery monitor is critical for Li batteries, voltage measurement is practically useless.
RT has stated they will reintroduce the Coach Connect system that does provide state of charge info, maybe based on shunt based measurements inside each Ecotrek but maybe not...
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Old 08-06-2017, 06:31 PM   #533
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I'd like to know how you are figuring out the remaining capacity ............. Is it just a total guess?
Using this SOC table that I shared here that somebody else made, and which seems to be right in my experience (the 13.6 for confirmed fully charged batteries seems accurate to me).

https://convotrek.blogspot.com/2017/...s-on-heat.html
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Old 08-06-2017, 07:00 PM   #534
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That chart is way, way, different than anything I ever recall seeing for lithium. Most show them staying much flatter in the middle range, kind of like this one that shows (to one decimal) the same voltage at 13.2v from 30 to 70% state of charge. The actual voltage of the flat center, I think can vary a bit based on temp, also.
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Old 08-06-2017, 08:15 PM   #535
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The Master Instruments chart shows 20% SoC being 13.08V whereas the chart WingedRyno is using shows 13.1V being 50% SoC.

12.44V on the Master Instruments chart indicates 5% SoC whereas the chart WingedRyno is using assumes 12.4V being 20% SoC.

It appears that the chart WingedRyno is using was someones best effort / best guess but likely not accurate.

Another clue as to the inaccuracy of the chart WingedRyno is using would be that it is unlikely that volstart kicks in at 44% SoC. It's more likely that it would trigger closer to 10% SoC than 44% SoC.
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Old 08-06-2017, 08:28 PM   #536
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Are the extra modules still in the $3500 range or have they come down?
I think from the outset they have been around $2500 per 200ah module. The 400ah setup is now $4992 and the 800ah version is $8684 so there is some savings in the higher ah units. But it's a little sneaky because their $3913 GU option also includes 2 additional AGM batteries for which they otherwise charge $871if ordered as a discrete option. However, if you select the lithium option, they delete the AGMs from the GU option but provide you no credit for their value.
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Old 08-06-2017, 08:31 PM   #537
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The whole "how much power do I have left" gets pretty complicated for an Ecotrek, kind of like having "reverse Peukert" on steroids .

If you discharge the module very quickly, in an hour for instance, you only lose about 4ah to parasitic. If you discharge the module over 24 hours you lose a whopping 96ah to parasitic. If you put a monitor on, about the only way you could be accurate would be to also have a stopwatch running to know how much to address the monitor reading. The loss in one module in a day is very close to two days use for use, even with the compressor frig (depending on weather). All this assumes a 4ah per hour parasitic per module, which may or may not be correct. Has anyone timed how long it takes to run a module from full to shutoff with no loads on it?
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Old 08-06-2017, 08:41 PM   #538
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The whole "how much power do I have left" gets pretty complicated for an Ecotrek, kind of like having "reverse Peukert" on steroids .

If you discharge the module very quickly, in an hour for instance, you only lose about 4ah to parasitic. If you discharge the module over 24 hours you lose a whopping 96ah to parasitic. If you put a monitor on, about the only way you could be accurate would be to also have a stopwatch running to know how much to address the monitor reading. The loss in one module in a day is very close to two days use for use, even with the compressor frig (depending on weather). All this assumes a 4ah per hour parasitic per module, which may or may not be correct. Has anyone timed how long it takes to run a module from full to shutoff with no loads on it?
That would be an interesting test. Turn off the fridge and cover the solar and time it. Should give a pretty good idea of BMS draw.

When I have more time I'll try to find a carport or garage and time it.
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Old 08-06-2017, 08:42 PM   #539
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Some of you give RT credit for more sophistication that they probably deserve. They appear to set charge parameters based on voltage and not SOC. It seems to me that is what they are doing when they had to add the AGM battery to make Voltstart work.

Another thing they probably consider is the issue of needing to periodically reset your amp counter with a shunt based system. I've noticed on occasion you need to do that and it may be beyond the understanding of most of their customers and result in more warranty visits. Most folks seem to understand voltage.

From the testing I've done in my bus, I really don't see much difference between setting charge engagement on SOC or voltage. I don't set it for coming on so that I get the maximum depth of discharge - I suppose if you had a small bank, that might be necessary. Somewhere around 30-40% is fine, as the battery has more than enough capacity that it takes awhile to get down that low as it is. Also, the solar coming in is largely wasted if you are precluding charging until the battery were down to 10-20%.

I also never charge fully - I set it to shut off charging at 13.4 or 90%. That way you are using the middle band of the battery capacity, which reportedly will extend it's life significantly, or at least, prevent degradation.
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Old 08-06-2017, 08:48 PM   #540
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Quote:
Originally Posted by markopolo View Post
SoC curve of an LiFEPO4 cell (4 cells in series in 12V systems)



There's so little voltage difference between 90% SoC & 20% SoC.
I agree that using voltage as a parameter for measuring SOC is certainly inferior to a shunt derived SOC display and adding 3 digit voltmeter registering 100mv increments is practically useless for measuring a lithium battery SOC. However, the 4 digit meter I have that displays 10mv changes provides sufficient sensitivity to permit a barnyard interpolation of our lithium battery state.
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