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Old 08-12-2016, 11:16 PM   #331
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Originally Posted by wincrasher View Post
Could it be they are trying to account for the voltage sag you'll see in a rapidly depleting battery with a large load on it from the inverter?
They also need to set the trigger voltage high enough to avoid the inverter low battery voltage shutdown under heavy loads. I think a manual reset is needed on the inverter they use after a low voltage shutdown.
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Old 08-13-2016, 12:09 AM   #332
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Thanks, I will certainly consider both of your suggestions.
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Old 08-13-2016, 12:13 AM   #333
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I don't understand the fascination with voltmeters for SOC determination. They are barely better than the idiot lights, unless you have a designated fixed load you can hook up to get a more accurate, loaded, voltage reading.

It is not rocket science to put in a shunt based battery monitor, even with the sealed modules. Many can be programmed with any parasitic losses, so the 5 amps could be taken into account (unless it is so much it is out of range!). Other lithium providers put in SOC monitors (the one Greg linked a while ago does), so the only reason I can think of that would keep Roadtrek from doing it would be then the customers could see how much power is getting wasted.
I haven't had the opportunity to work with SOC measurements of large lithium batteries but I have done measurements with smaller lithiums used on electric assist bikes and with four digit measurements, you can put together a table that establishes the state of charge with usable accuracy.

That said, there is no question that shunt driven monitors are the way to go. With a setup like ARV provides this is easy to do because all of the batteries are either on or all off. RT makes this more difficult to implement because they permit the user to bring batteries on or off in a multiple independent battery setup. To initiate any of these monitors, the ah capacity has to be inputted. Consequently, with the RT arrangement, if the user takes one or more of the batteries off line, while the voltage reading may be accurate, the State of Charge readings would not be accurate unless the user reconfigured the ah capacity accordingly. So, with RT's setup you would either require multiple shunts and meters or a program written for the BMS that would determine how many batteries are on line and provide some correction information to the metering system. I'm sure it's doable but it's certainly more complicated.
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