Is a Shunt Required?

[menalice]

I notice that most of the wiring diagrams indicate a "shunt" on the negative side of the DC system. I have the MidNite Classic 150, with the positive circuit protected by circuit breakers before the "+PV In" and after the "+Battery Out".  Is the Shunt required if I am not using an ampmeter to monitor the batteries?

[tecnodave]

The purpose of the shunt is to divert most of the current around the ammeter so if you are not using an ammeter or other current measuring device including the Whizbang jr. Or battery monitoring device you will not need a shunt. The Classic has internal current monitoring.

[Westbranch]

If you want to get/use the recent addition to the capabilities of the Classic, you will need a WhizBangJr and the shunt to attach it to... Otherwise you don't need it.

[ClassicCrazy]

The extra $75 that a shunt and whizbang cost is well worth it for the extra system monitoring capability and perhaps control capabilities  that you can utilize with it.  Easier to put it in initially than to have to go back and install it later.

[tecnodave]

I gotta agree with Classic crazy on that,  I have two shunts on my system one for the Whizbang jr and a trimetric battery monitor and the second for digital meters that use a different value shunt. At the cost of batteries it is well worth the cost of some kind of battery monitor to protect your battery bank.

Note the digital meters are from brainy deal on Amazon and are $16.99 each 200 amps/200 volts combo LCD panel meter with included remote shunt. I have two on my system, one at PV input and one at Classic output. They were originally used with a cheaper controller which did not have good meters. Unfortunately they do not use the 50 mv. Standard in the solar industry. (They are 75mv.)

Batteries are one of the most expensive parts of the system and are usually the first to fail, so a bit of monitoring is well advised

[Westbranch]

TD, boB wrote a bit about how to use a non standard shunt wither here or on NAWS, not too long ago...might help you out in using it.

[menalice]

Looks like I need to check out the whizbang to see what all the bells and whistles are about - more comments to come after further review. I usually just use a hydrometer, but if this is accurate enough I guess I could do without crawling under the slide out to access the batteries.  Thanks for the comments.

[tecnodave]

WB, the shunts I am using are measuring different values, the 75 mv shunts only look at the Classic input and output and are there to help calculate which string voltage to use into the Classic or the tracers that it replaced to achieve maximum efficiency.  In full sun I normally use 34 volt strings with strings of 2 36 cell mono panels in series on each string in parallel with 1 72 cell poly panel on each string and do not use my CdTe panels as that would overload the Classic, when foggy season sets in I use 4 36 cell panels in each string , 2 72 cell panels in series and all of the 154 cell CdTe panels in parallel , I guess I got lucky in this mixed bag of panels as the v.m.p. of all the panels strings are within 1 volt of each other. The 50 mv shunt measures total battery current. The Whizbang is new and I am unfamiliar with it as yet. Bogart Engineering is in my neighborhood right up the way in Bolder Creek so I have been familiar with their product for some time. I did read boB's notes on using non standard value shunts, but I am using them only for the brainy deal digital voltmeter/ammeters. The quality of the brainy deal shunts and meters is questionable and I was only able to get reasonable accuracy by feeding the meters with a regulated 9 volt power supply and re calibrating them with my Fluke 87V to achieve 1% accuracy.