How to measure DC current

[bukzin]

I am wanting to measure some of the loads (amps) on my coach.

My standard multi-meter does not support this.
Thinking about options.


What are you folks using and any tips on ways
to get reliable readings?

Thx

[jrnymn7]

Another handy use for the Kill-a-watt, is the ability to see how many KW Hours are consumed while charging off "borrowed" shore power. For example, I can show my brother that I only use 20 cents worth of grid power to charge my bank for 4-5 hours.

It could also help verify one's electrical consumption when paying for hydro at a campground.

[jrnymn7]

LarryJM wrote:

jrnymn7 wrote:
bukzin,

keep in mind, you cannot measure amperage across a double cord (i.e; black and white inside casing) with a clamp meter. That's where the kill-a-watt comes in handy. The clamp meter is for checking current thru single battery cables and such.

If you can use a kill-a-watt you can use a clamp on meter for much better readings by using a line splitter so your concern is a non issue. You can find line splitters in various configurations from X1 to I think up to X10 or 100. Plus a clamp on will measure DC where a kill-a-watt is only good AFAIK for AC.

Larry

Hey, Larry.

Yes, I am aware of those line splitters. I was just giving the OP the heads up, in case he thought he could use a clamp meter (alone) for measuring ac current. I have both a kill-a-watt and a clamp meter, and am very satisfied with both. The uni-t's are a good little meter, but they do tend to read a little low. And yes, the kill-a-watts are ac only, but very handy for reading line voltage, amp draw, and wattage while determining the efficiency of a charger, and thus its compatibility with one's genset.

[vermilye]

I use an Amprobe clamp on AC/DC multimeter for individual circuits, however installing a TriMetric 2025 battery monitor is even more useful. You can easily keep track of amp hours in & out of your batteries; useful for dry camping.

[Chris_Bryant]

When I replaced my last meter, I chose one without high current measuring capability (it does read micro amps, which I use to troubleshoot ignition modules). I added this Tenma AC/DC clamp, which will work if you have a millivolt range on your meter.

As a note- you can also test current by using the standard blade type fuses as a shunt- turn on the load, measure the voltage between the two side of the fuse (on the top). While I don't have the figures in front of me, fuses are a reasonably well calibrated resistance- different for each value. Often you can do this just to detect a load- if you see a voltage between the fuse legs, there is a draw on that circuit (or the fuse is blown :))

[2oldman]

12v amperage usage in RV

[wa8yxm]

Most standard multi-meters will meter up to 10 amps wheh put in series with the load (Easiest way is to pull the fuse and repalce with the meter and an in-line fuse holder).

However for bigger loads go to Sears. A Crafstman model 82369 will do up to 400 amps clamp on, However it does NOT indicate direction of flow when used clamp on.

[LarryJM]

jrnymn7 wrote:
bukzin,

keep in mind, you cannot measure amperage across a double cord (i.e; black and white inside casing) with a clamp meter. That's where the kill-a-watt comes in handy. The clamp meter is for checking current thru single battery cables and such.

If you can use a kill-a-watt you can use a clamp on meter for much better readings by using a line splitter so your concern is a non issue. You can find line splitters in various configurations from X1 to I think up to X10 or 100. Plus a clamp on will measure DC where a kill-a-watt is only good AFAIK for AC.

Larry

[PaulJ2]

pnichols wrote:
The best thing would be to install a permanent ammeter in your coach.

First, install what they call a "shunt" in the main negative lead of your coach battery. Then, run a wire from this to wherever in the coach you would like a small and inexpensive digital meter to read current. (The shunt is not expensive either.) The meter will read negative (a "-" symbol ahead of the current reading) if current is going out of the battery and will positive (a "+" symbol ahead of the current reading) if current is going into the battery.

I've had this for years and it is real helpful for monitoring what current every 12V item in the RV is using and how well the batteries are performing and getting charged. I velcro'd the digital ammeter right on the dash where I can watch it as I drive or camp.

I have something similar. A permantly mounted 30-0-30 round analog ammeter from an old rideing mower. Shows what is going into or out of the battery at all times. Converter is 30 amp unit so works great.

[SCVJeff]

jrnymn7 wrote:
bukzin,

keep in mind, you cannot measure amperage across a double cord (i.e; black and white inside casing) with a clamp meter. That's where the kill-a-watt comes in handy. The clamp meter is for checking current thru single battery cables and such.

Unless you have THIS
It's also fun to freak out friends by clamping onto the x10 coil to ask your friend why his LCD TV draws 1000 watts.. 🙂

[Gonzo42]

Harbor Freight Ammeter Plugs into fuse socket and reads current.

I believe there are more than just this one.

[tenbear]

Sometimes I use my multimeter, sometimes my DC clamp-on and if I want to see how much current is flowing into or out of my battery I use the built-in ammeter. (Built in by me.) Perhaps you could give more details of what you want to measure.

[RJsfishin]

If you want to go permanent, this works great, 50 amp w/ shunt.
Others available in 30 amp to 300 amps
http://www.ebay.com/itm/100V-50A-DC-Digital-LED-Amp-Volt-Combo-Meter-w-Shunt-f-12v-24v-HHO-EV-car-So...

[dclark1946]

A DC clamp on Ammeter makes it really easy to make current measurements without breaking a connection. Sears sells a really nice DMM combined with DC/AC clamp on Ammeter. I have both the Sears unit and an Extex true RMS clamp on Ammeter. Great for measuring load and charge current.

Dick

[korbe]

My 5 dollar volt meter has an amp setting that I used to measure all my DC loads. I disconnected the positive lead at the battery and touched the meter prongs while my DW turned everything on and off.

[jrnymn7]

ah, good call. I wasn't even thinking along those lines.

The trimetric is mooey $$$, but very accurate, amp hour wise.