Power Meter for Van Battery

Stratman77 · Senior Member

Power Meter for Van Battery

sandsmere · Guru

I got one from Auto Cheap. $29.

dorian · Guru

I would look for a device that doesn't insert itself into the current path. Silicon Chip magazine had a design for an ammeter that clamped onto the cable and used a Hall effect sensor. It was good for 150A continuous usage (up to 900A if core is demagnetised afterwards).

archive.siliconchip.com.au/cms/A_30669/article.html

I wonder if there is a combo power meter that uses the same non-invasive approach.

Stratman77 · Senior Member

That's interesting. I think the shunt in these devices is around 0.1 ohms. Anyway, I could not measure a voltage drop at all across it. But theoretically, the hall effect device is way out in front!

PeterD · Guru

Chris, may we have a link to it please?

Stratman77 · Senior Member

This looks identical to the one I bought, but I can't be sure it's the same seller. It's $1 cheaper though!

www.ebay.com.au/itm/DC-90V25A-Digital-Amp-Volt-Combo-Meter-Battery-Capacity-Power-Charge-Discharge-/161475944698

Delivery took about 2 weeks after I ordered it October 13. The instruction sheet is also very well done and not in Engrish.

One thing I found the terminals unsuited to normal 25A round eyelets, I found some reasonably heavy spade terminals the right width and drilled a hole through for the fixing screw. Works well.

While I was doing this I took the opportunity to sort out an ugly bunch of in line fuses by using a small 10 fuse panel from Jaycar. I had to modify the centre live bus to provide 12v from various sources but it's now quite neat and tidy and I won't have to sort through a bunch of fuses to find the right one! The fuse panel and the meter fitted neatly into a cheap plastic project box also from Jaycar.

I'm happy to provide my wiring diagram if anyone is interested.

-- Edited by Stratman77 on Saturday 8th of November 2014 04:31:58 PM

-- Edited by Stratman77 on Saturday 8th of November 2014 04:41:28 PM

-- Edited by Stratman77 on Saturday 8th of November 2014 04:42:05 PM

-- Edited by Stratman77 on Saturday 8th of November 2014 04:42:33 PM

-- Edited by Stratman77 on Saturday 8th of November 2014 04:44:07 PM

dorian · Guru

I found a similar looking unit (DCM9030C). It's specified for 30A.

www.keepandshare.com/userpics/k/e/v/i/n2009/2013-04/sb/dcm_indicator-66964393.jpg
www.keepandshare.com/userpics/k/e/v/i/n2009/2014-08/sb/9030c_rear01_30a-1308174.jpg
www.keepandshare.com/userpics/k/e/v/i/n2009/2014-08/sb/90xxc_voltage_state_of_charge-76341880.jpg
www.keepandshare.com/userpics/k/e/v/i/n2009/2013-05/sb/9030_discharge_new-91681656.jpg
www.keepandshare.com/userpics/k/e/v/i/n2009/2013-05/sb/9030_charge_new-68597009.jpg

I wonder if it's the same device, but with a higher rated sticker.

As for an 0.1 ohm shunt, that seems far too high. At 25A the voltage drop would be 2.5V and the dissipation would be 62.5W.

Stratman77 · Senior Member

Being a newbie at this, I will have to remember that there will always be members out there who know so much more than I do about any given subject and are happy to correct me when I stuff up. Dorian, you are quite correct with your application of Ohm's law. That will teach me to double check my statements and not just grab numbers out of the air. The shunt value is not specified, but obviously would need to be considerably lower than 0.1 ohms. I suspect that the DCM9030C is virtually identical to mine as the rear connection block IS identical. If you look at the snag attached of the rear of a 9030C, you will notice that the label says DC 0-90v, 0-20A. How peculiar! Strange things go on in China.... In any event, whether or not they are the same, it is a great little device for the job and I doubt if I will see charging currents anywhere close to 25 or 30 amps! Maybe the only difference is the label....

dorian · Guru

I was just looking at the specs for a 50A DC watt meter. It has a "precision Alu-Chrom current sensing resistor, with only 0.001 Ohms resistance". Maybe the DCM9030C (or is it DCM9020C or DCM9025C?) has a similar shunt.

Stratman77 · Senior Member

Hi, Dorian! 0.001 ohms? Wow. I doubt if my DMM would even measure that! There is probably more resistance in the meter leads. It certainly is a strong possibility, but you would need super sensitive electronics to work at that level!