Measure current flow - Thumper

Can't say I've heard of a DC tong meter?

I was imagining hooking an auto ammeter in series, but if I want to measure the flow in as well as out I'll need to hook it internally somehow.

I could also put in a ammeter on one of the sockets but that would only work on that socket and obviously not measure the flow in. This isn't a real need but would be interesting seeing how much is coming in when driving.

The tong meter is also known as a clamp ammeter. It relies on the magnetic flux generated from the current flowing through the wires. Some of these are only good for AC, but others incorporate a Hall Effect device and can measure DC current as well.

I must be clamped around only one of the conductors, if it is clamped around two of them then the magnetic flux will cancel out and you will not get a reading.

I have two of them and can use them to measure the peak current drawn from the battery when starting the engine.

They also have voltage and resistance measuring capability and some even have temperature as well.

See the following link to Sidewinder who have such a device, Jaycar will also have them.
Sidewinder

That looks exactly the sort of thing I'm after, and the price is decent as well.

I'm not really following the instructions though. Where would I need to connect it?

Okay, more research.

Shunt info here:

http://en.wikipedia.org/wiki/Shunt_%28electrical%29

Basically you just interrupt the negative line to the battery?

Yes, the linked instructions could be clearer.

The meter is in two parts, the digital readout panel can be placed where ever convenient, on the Thumper box or nearby. The current shunt which is actually a very heavy duty resistor is inserted into the negative cable which connects to the thumper battery inside the box. These two modules are interconnected with 3 wires which do not carry current so can be light-duty such as a length of 3-core mains flex. If the panel meter is on the Thumper box with the shunt the 3 interconnections could be made with light-duty auto cable or hookup wire.

The function of the shunt is to generate a small voltage proportional to the current passing through it and this small voltage is received by the panel meter and causes it to display the current passing through the shunt.

Just be aware that no more than 50 Amps should pass through the shunt or it may be damaged so do not use the thumper for higher loads such as jump-starting the engine unless you connect directly to the thumper battery without the current passing through the shunt.

That's a good point about jump starting. I may need to get a higher rated unit as I do use it for this from time to time using the jumper cables on the thumper.

Or I could just connect it to the negative line on the cig lighter socket? This would only measure flow on that socket and wouldn't measure flow in, but still better than nothing.

Tony, I have prepared a schematic which may be clearer for you.

Image Could Not Be Found


Thumper units and their copies vary somewhat in arrangement but I assume that yours has an Anderson plug which you use to connect for charging and for jump-starting. One way of overcoming the shunt load problem is to fit a second Anderson socket which is connected directly to the battery terminals and use that for jump-starting without the current passing through the shunt.

Otherwise, as you say, connect the shunt only to the cigar socket but forego reading charging current.

Allan, that schematic is great. You should send it to Jaycar!

My thumper has two anderson connections. One is a lower current one for connecting to the 50A charge kit. The other side has a much larger high current connection that you plug the jumper leads into for jump starting. I also connect the battery charger to these leads when I use it.

So I may be able to use your suggestion?

I'll see if I can drop down and take a photo of the inside of the unit.

Tonydav,

If you connect the shunt to the negative cable that feeds the cigarette/merit sockets
You will be bypassing the heavier duty jumper anderson socket and all should be good.

Not quite all good Bill. Tony said he would like to be "seeing how much is coming in when driving."

I've attached a photo of the thumper insides.

I'm not sure it will be possible to do what I want with one ammeter.

If it does the current out that's the main thing though.

To explain the cabling, the positive runs to the big anderson from all batteries and then a small line to the 3rd socket from the left.

Negative is much the same with the small black cable also goes to the third socket from the left.

The small anderson on the left takes the 50A charge kit and goes via some plate in the middle (don't know what this is for) to the battery.


Pic of thumper insides

Tony, that pic is good and shows the arrangement pretty clearly.

The "plate in the middle" is an overload circuit breaker to protect the cigar sockets. It is in lieu of a fuse.

That looks cool. Where did you get it?

Looking at my thumper pic, where did you "insert it"?

That Turnigy unit looks pretty good Andrew and I found them on ebay as low as $32. I would be interested myself if I did not already have metering installed.

Tony, this still would not handle starter motor currents, but if you wired it to the smaller Anderson socket and ensured that the cigar sockets were also connected there, then arranged to charge the Thumper through that Anderson, you would achieve your original wishes and also be able to read Ampere-hours as well as current & voltage.

So what you're suggesting is to move the wire for the sockets from the big anderson to the small connector?

Would I need to move the positive as well as the negative? I'm thinking not but not sure.

Alternatively, given this unit also gives Ah, if I just connected it into the negative of the socket wire it would give me a reading of how much was used over a period and not just a reading at the present time.

I can see this being useful and I imagine if I mixed it up with the inflow from being charged it wouldn't work (I imagine the Ah reading would reduce from being charged????)

Realistically 99% of the time all I'd care about was how much was going out. I was just looking to check the in reading to ensure all was wired correctly.

Tony,

They are available from Ebay etc or from hobby stores (radio controlled gear etc) eg www.hobbyscene.com.au

For a simple install, i have powerpole connectors (the smaller version of the 50A anderson connectors) on either end, with numerous "adapters" for multiple uses eg powerpole to SB50 etc. That way it is flexible and can measure one or a number of devices as appropriate.

Having all the low current feeds (ie. not the large connector SB175?) going through it would measure those feeds, though you need to add a reset switch if measuring watts etc.

Hope that helps.

Andrew

Tony, I cannot tell if the Turnigy measures the current in the negative or positive conductor so to be sure it would be necessary to connect using both. Just be sure that current to the larger Anderson does not pass through it.

This looks like the way to go.

There's an interesting thread on it here which gives some more info on their capabilities:

http://www.trailersailerplace.com.au/forum/viewtopic.php?t=5593&sid=1e6f4743470d8ec9d0d0fcffc933c819

Andrew, I'd really be interested in looking a picture of your setup. I was thinking of something along the lines of what it sounds like you've done.

Tony, several things I learned from that link were:

1. The current sensing is in the negative conductor.

2. The metering accuracy can vary from reasonable to poor.

3. The device has a self-consumption of 14mA. This is not excessive but leaving it permanently connected will drain some capacity from your battery. If this was of concern it could be arranged with only the negative current passing through the device and the positive wire being connect to a +ve source via a switch or pushbutton so that it only displays when required. Of course in this mode, the integration readings of Ah or Wh will be reset to zero when the device is switched off.

Oh, and one other thing:

4. It is not bi-directional. It reads current flow in one direction only so the one unit cannot be connected to indicate charge and discharge unless it were connected via plugs so that it could be reversed.

In case anyone is interested in these, Hobbyking.com sell these for about $24 plus $6 delivery.

They also sell the original genuine Watts up version for about $50. If you wait on the page you will normally get offered this at about $40. Very good value for a US made product.

I have one of those clamp meters from Derek, and am very happy with the purchase.

If you want to test the current draw of your fridge, or input of panels, or your alternator etc etc a handy piece of equipment.

I wouldnt hesitate to reccomened one.

Trains

Something else to investigate.

Great help here. I really just need to work out what information I want to be displayed and the appropriate tool.

Bruce, I'm having a little trouble finding this product on their site. Any chance you could send a link?

I knew once I posted that last I'd find it. Here:

http://sidewinder.com.au/page153aa.html#Anchor3

Strange it didn't come up when I did a search on "clamp meter".

Have ordered one of these as I can see it being useful a host of times.

May yet still decide to mount one of the other units but for the present time this clamp meter looks really cool.