Doc Watson meter, how to connect to 48v SLA setup...

[GreatScott!]

Hello,

Not sure if this topic has already been done but I am looking for some advice on how to connect a doc watson meter to a 48v SLA battery pack system, I can't get it to work.

On these meters, there are a four wires to account for in total.....two wires, a black and red wire coming from the left (Source) side of the meter and two other wires, black and red again coming from the right (load) side of the meter. I am using an alltrax golf cart controller, I first tried to connect the Red (positive) wire from the source side to the main power wire from the battery, I did this at the controller + tab. I also connected the RED + wire from the LOAD side to this same location. I then connected the BLACK, negative wire from the SOURCE side to the negative terminal wire of the battery where it is connected to the controller tab, I also connected the BLACK negative wire from the LOAD side to this same location, essentially connecting the meter across the battery. This doesn't seem to work as it only displays overall pack voltage but I get no other readings such as KW and Ah etc. How is this thing supposed to be connected?

cheers.
Jonathan-

 

[Johnbear]

The source wires should go + - to the battery and the load should go + - to the controller. That is how I hook up mine.

 

[GreatScott!]

I believe I did connect it the way that you are describing the first time I tried it, here is a schematic of how I connected it, what am I doing wrong?

 

[Jeremy Harris]

First off, the motor current has to return through the Doc Watson negative (black) lead, as there is an internal resistive shunt that is used to measure current.

The black lead from the "source" side goes to the battery negative, the black lead from the "load" side goes to the motor/controller negative, so that the motor current flows through the Doc Watson. There should be no other connection from the battery negative to the motor/controller.

The second point is more important. The internal shunt in the Doc Watson won't handle high continuous current, plus the Doc Watson wiring is really far too small for something like an Etek motor. IIRC, the doc Watson is good for around 30 to 50 amps continuous, 100 amps maximum and they provide advice on how to modify the device to use an external shunt with a higher rating if you want to operate at higher average currents.

I've modded my Doc Watson, by removing the internal 0.001 ohm shunt and wiring it up to an external one, fitted into the total power system return lead. There are full instructions on the RC-Electronics site, here: http://www.rc-electronics-usa.com/special-mods.html. RC Electronics also supply the big shunts needed for running high continuous current as well.

Jeremy

 

[commanda]

I have just fitted a Doc Wattson to my EVT the same way Jeremy has, using an external shunt, but powering it from the 12 volt converter using the auxiliary power input.

The 2 red wires are connected together internally, you only need to connect one of them.

In your diagram, the batt neg should connect to the Doc W source neg, and the Doc W load neg to the controller neg. There should be only one wire terminated at the controller neg.

But, with an Etek, you'll need an external shunt. You need to read the pdf Jeremy linked to.

Amanda

 

[GreatScott!]

Lol....I wish they would have explained this on the website before I bought it. I mean forget it, look how big that high powered shunt is, there is no way I could fit that to my already cramp cockpit. I will stick with my nice simple current LED meter. Thanks for all the advice though.

FOR SALE: DOC WATSON METER

If anyone wants to buy a brand new DOC WATSON meter at a discounted price let's talk.

CHEERS.

 

[Jeremy Harris]

Well, I guess they do have a lot of useful stuff on their website, including the ratings of the Doc Watson and Watts Up, but maybe they don't exactly spell out on the front page that the meter needs mods if it's to be used on a high power EV.

The current shunt isn't that big, mine's maybe a couple of inches long and an inch and a bit tall. It's easy enough to mount to the motor/controller terminal, using a short copper link.

One advantage of using the external shunt is that you don't need to run big wires up to the meter itself, it can be fed with thin wires, which makes installation a bit more flexible.

Jeremy

 

[GreatScott!]

RIght right, I understand.......however, if you have ever seen my setup, there would be precious little room to fit even that size of a shunt. I had to work hard trying to locate even the main power switch.