Your monitoring device/telemetry unit has an A/D converter in it. Many times they are 13 digits of precision. So 8192 discrete levels.
Say you are monitoring a current that is expected to range from 0-20 amps but using a 200 amp shunt, even if the telemetry has a setting for a 200 amp shunt, the problem is you have 8192 levels to represent all currents. So with a 20 amp shunt and an agreeable telemetry unit, you can measure down to 20/8192 or 2.4mA steps. Your precision is +/- 2.4 mA Installing the 200 amp shunt in that same circuit, now your precision is +/-24 mA And if the A/D is a 10 bit unit, the precision would be 200/1024 or 195mA. If you are not worried about granularity, then it doesn’t matter. Me, I like as many digits of accurate precision I can get. From: Charles Regan Sent: Wednesday, September 06, 2017 7:38 PM To: [email protected] Subject: Re: [AFMUG] Cost effective battery charging and monitoring device But if you have the correct ohm resistance of the shunt? Your monitoring device should have a setting for that? With the ohm reading, it should be pretty accurate. I'm using one of those shunt (150A 20$) on my electric bike and I get the same amp draw reading on my fluke meter. Max I draw is 65A or 4kW so that's higher than most wisp battery backup system. That's my fuel gauge so it needs to be pretty accurate. Here's the meter I use on my bike , no network connection but serial data output and the monitoring of amp, watts, voltage and AH used is there. www.ebikes.ca/product-info/cycle-analyst.html Le mar. 5 sept. 2017 à 18:53, Chuck McCown <[email protected]> a écrit : The higher the amperage the shunt, the less precision you get from the system. From: Charles Regan Sent: Tuesday, September 05, 2017 3:52 PM To: [email protected] Subject: Re: [AFMUG] Cost effective battery charging and monitoring device Why just change the shunt for one like this? That's a 600A shunt. 45$ Deltec 600A Ammeter Shunt http://www.electricmotorsport.com/deltec-600a-ammeter-shunt.html Le mer. 30 août 2017 à 14:29, George Skorup <[email protected]> a écrit : Yeah, about that. I wouldn't use those on 12VDC systems. Too much current. I've burned up a couple of the 10A shunts on Traco BCMUs that were running around 200W load on battery. 200/13 = 15 amps. Ungood. One site at about 225W, first time it went to battery, the shunt went kaput after 10-15 minutes and the site went down. I'm hoping Forrest comes up with some Hall effect stuff or even plain 20+ amp shunts that can be used on the SiteMonitor's existing 100mv input. Hall effect is nice because you don't have to be "in" the circuit. But I'll take what I can get. On 8/30/2017 10:26 AM, Adam Moffett 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
