What is your max charging and discharging current? That is the first thing. Second thing is what is the voltage range of the device you are using to measure the current.
For example, if you never expect more than 50 amps and your telemetry will measure 0-1 volt on the analog input, then your shunt needs to be less than 1/50 or .020 ohms. So when 50 amps is flowing, there will be 1 volt across it. That is equivalent to 20 feet of #10 wire. You don’t want to use a 10 volt input because if 50 amps is creating 10 volts across the shunt, not only do you lose 10 volts with which to power your load, the shunt is going to crank out 500 watts of heat under full load. The lower the shunt resistance the better because shunt voltage is subtracted from the voltage used to power your equipment and no need to make any more heat than you need. However very low resistance shunts make very low voltages and analog telemetry inputs may have digitization errors and noise errors with really low inputs. Normally battery current is not so critical that those errors are a concern. From: Ryan Ray Sent: Wednesday, August 30, 2017 11:28 AM To: [email protected] Subject: Re: [AFMUG] Cost effective battery charging and monitoring device How would you properly spec out a shunt given a certain number of batteries? On Wed, Aug 30, 2017 at 8:39 AM, Adam Moffett <[email protected]> wrote: it puts out so many millivolts depending on how many amps are moving through it, so with a volt meter you can monitor what your load is. ------ Original Message ------ From: "Steve Jones" <[email protected]> To: "[email protected]" <[email protected]> Sent: 8/30/2017 11:36:38 AM Subject: Re: [AFMUG] Cost effective battery charging and monitoring device what does the shunt do in this case? On Wed, Aug 30, 2017 at 10:26 AM, Adam Moffett <[email protected]> wrote: Yeah, up to 10 amp. ------ Original Message ------ From: "Chuck McCown" <[email protected]> To: [email protected] Sent: 8/30/2017 11:18:36 AM Subject: Re: [AFMUG] Cost effective battery charging and monitoring device I think Forrest has them on his site with the site monitors. From: Sam Lambie Sent: Wednesday, August 30, 2017 9:15 AM To: [email protected] Subject: Re: [AFMUG] Cost effective battery charging and monitoring device Parallel. Site Monitor! Now where can I get a shunt? On Wed, Aug 30, 2017 at 9:09 AM, Chuck McCown <[email protected]> wrote: 4 batts in series or parallel? Shunt + sitemonitor would be a better way to go and you don’t have to write code. From: Sam Lambie Sent: Wednesday, August 30, 2017 9:06 AM To: [email protected] Subject: [AFMUG] Cost effective battery charging and monitoring device Hey all, I am getting away from using APC at a couple of our sites and right now I have installed a Tripp-Lite APS750 connected to 4 Deep cycle marine batteries for a total of 404 aH system. I'd like to be able to monitor the discharge rate of the batteries when power is out remotely. What have you guys been doing to that effect? I'm thinking a Pi and a shunt and some quick scripting classes on Python to put it all together... -- -- Sam Lambie Taosnet Wireless Tech. 575-758-7598 Office www.Taosnet.com -- -- Sam Lambie Taosnet Wireless Tech. 575-758-7598 Office www.Taosnet.com
