RV & Marine Battery Monitor for cumulative amp hours

[markopolo]

Looking for some comments re: the Doc Wattson R102 DC Ammeter & Amp Hour Meter
http://www.rc-electronics-usa.com/ammet ... nitor.html
PDF Manual: http://www.rc-electronics-usa.com/docs/ ... manual.pdf

Knowing cumulative amp hours would be handy. A Trimetric would be nice but I'd like to find something that counts amp hours (daily or weekly) that costs much less.
The cheaper units only seem to count amp hours either incoming or outgoing depending on where you install it. Net cumulative amp hours for the day (or week) would be more useful to me.

[markopolo]

Note the three wire connection in RV's.
http://www.rc-electronics-usa.com/ammet ... ction.html

Three-Wire Amp Hour Meter Connections

This arrangement requires only two heavy gage wires to carry the negative lead current and so is best for remote testing and monitoring. The third, plus, wire can be lighter gage (e.g. 20 gage or heavier) as it only carries the small current required to run the meter itself.
The three wire hookup also allows higher current operation as the heat from power dissipated by high current in the plus wire is no longer present.
Bottom most diagram shows use of reset button with auxiliary power connector cable.
See our Meter Links page for a handy wire resistance and voltage drop calculator.
Please Note that many other meter uses and arrangements are possible.
The meter's User's Manual has more details and safety precautions.
A battery or other voltage limiting device must be connected between the meter's red and black leads anytime the load is connected or disconnected. The battery prevents inductive loads causing damage to the meter.

[markopolo]

There's a cheaper one (around $30.00) that can also be wired in using only three wires not four. It is a Turnigy 130A or also known as a GT Power 130A
MrWizard on RV.net provided a photo of his three wire install here:http://www.rv.net/forum/index.cfm/fu...6.cfm#25052286

and someone else here: http://webby.natcoa.net/Analyser/Analyser.html looks to have installed it using all 4 wires in a lower amp draw installation measuring only his fridge.

[markopolo]

I went ahead and bought two even less expensive battery monitors. Total for the two including shipping was only US$ 35.30 http://www.ebay.ca/itm/261043830897



I think I'll wire them in like this:

[battery negative] to [source *meter #1* load] to [load *meter #2* source] to [common neg buss for converter, inverter, solar]

I could leave the inverter out of the mix but I would like to get that data.
I won't measure the charge from the alternator.

I'll tap into the manual battery switch to power both units at their source connection point. That will let me easily reset them. I have 50 amp and 80 amp thermal breakers and 100 amp fuses on hand. I also have Anderson connectors, ring connectors, etc. I have enough wire also. It'll be nice to keep this whole project under $40.

I'll limit the use of the 14ga wire to 4 inches in total if I can. Maybe I can open them up and put 10ga in them if it will fit.

I think this will show me cumulative amp hours in and out. The counter goes to 65 amp hours and resets to zero. It will count watt hours to 6,554 though. The data will be nice to have if I camp without hookups for three days or more. I doubt I'd look at it for one or two days dry camping.

The small gauge wire causes me some concern but other RV'ers have used units with the same specs. They're only on the negative wire, not the positive. I can't see my system ever pulling or pushing more than 40 to 45 amps through them.

I think this is the user manual for the units I purchased: http://www.evpower.com.au/IMG/pdf/Watt_ ... r_User.pdf It sure looks like it.

I copied the following from the manual:

2.1 Features
? Measures energy (Wh), charge (Ah), power (W), current (A) and voltage (V)
? Connector to use an optional receiver battery for measurement down to 0 V
? Accurate & precise ?0.01 A current and 0.01 V voltage resolutions
? Measures peak Amps, peak Watts and voltage minimum (sag)
? Rugged -handles 50 A continuous and 100 A peak at 60 V
? 14 ga., super fine stranded, high temperature, silicone rubber insulated wire

[markopolo]

Moved topic to Tweaks Mods and Projects
__________________________________________________ ____________________________________________

Now that I bought something I guess this is a project
I think I'll start out measuring lower amp draws when I first install these units. It's only $35 but no point in letting the smoke out of them too soon.
Maybe I'll get to use up all these spare bits and pieces I have.

[markopolo]

Here is a good technical review from a camper / trailer forum of the meter I purchased. (I'm 99% sure it is the same meter)
http://myswag.org/forum/index.php?to...2426#msg122426

[markopolo]

Related links:

Remote shunt on a Turnigy: http://endless-sphere.com/forums/viewto ... =2&t=21976
Watt's Up schematic: http://endless-sphere.com/forums/viewto ... 04#p242804

I've got a lot of reading to do

I've been thinking about using an external shunt. I guess I just don't understand how the small internal shunt can measure high amperage without melting.... Any ideas?

[markopolo]

External shunt for "Watt's Up" and "Doc Watson" meters:

http://www.rc-electronics-usa.com/special-mods.html

Using with an external current shunt resistor instead of the internal shunt
The shunt inside both the Watt's Up and Doc Wattson is a 100 Amp peak, 100mV type. i.e it has 0.001 ohm resistance. It's in the negative i.e. black lead.
Using an external current shunt resistor allows increasing the maximum continuous current of the meter. It also allows using small diameter wires to the meter as only the shunt needs the heavy current carrying wires.
If you have the necessary skills you can modify the meter for use with an external current shunt resistor like we sell on our site (of course, doing this will void the warranty). The CSA100-100 or CSB500-100 would be suitable. With the CSB500-100 (500 Amp) you would need to multiply all current related dsiplay measurements by five and you would use the full dynamic range of the meter. With the CSA100-100 (100 Amp) no corrections to display values are needed since this is the same value shunt (though with higher power dissipation) as is already in the meter.
To modify the meter you need to crack the case open and remove the internal shunt. See instructions for opening the case elsewhere in the FAQ.

[markopolo]

The watt meters arrived by mail this week. The LCD displays were a little off center so it was a perfect excuse to open them up. At $17 each there's not much money at stake.


Shunt










There's an adhesive pad inside so centering the LCD screens was easy.

I'm now planning to use these in parallel with a switch. With the switch closed the current will mostly bypass the meter. When the switch is open then current will flow through the meters and be measured. I'm doing it this way because the wire gauge and shunt size etc. seems small for RV use. The start up load of my air conditioner on the inverter would be too much for one of these meters. I can close the switch to avoid the big loads.



The cases are aluminum and could be painted or maybe mount the meters without the cases. There's lot of options with these.

Interesting thread here: http://www.fieldlines.com/index.php?topic=145653.0

[markopolo]

A little bit of progress. I've attached the two meters, an on/off switch and a large bypass switch to a board.







Two large negative wires (4 gauge or greater) will connect to the bypass switch. One will be from the battery bank and one will go to the converter, solar panels and all loads (all on a common buss).
One small positive wire will connect to the on/off switch to power the meters.

I put a bypass switch in the mix because the crimp connectors I used will not handle large loads. Normal mode will be with the bypass switch closed. Most of the current will bypass the meters.
When I want to measure loads for a fan, lights, solar in, pump etc. I can open the bypass switch and all current will flow through the meters.
The top meter will measure incoming power. In from solar and in from the converter.
The bottom meter will measure outgoing power. Out from the house battery bank.

I think this will be useful when dry camping when the loads aren't large. I'll be able to see the cumulative amp hours in from solar and the cumulative amp hours out from using the pump, lights, fan, laptop on inverter etc.

This is not setup to monitor large loads like running the microwave oven off the inverter. My guess is that it will be ok to maybe 20 amp hr max in short durations.

[markopolo]

I installed the two watt meters today. It is interesting to watch them and you can get a lot of data. I shot some video with my camera:

This one shows the amps in from the converter dropping quickly as the batteries near full charge. This is the input meter.
[youtube:1b2scbe0]DBv2WN97Sxo[/youtube:1b2scbe0]

Another video showing a Watt Meter measuring input from the converter/charger:
[youtube:1b2scbe0]Rs2VVTUBzjs[/youtube:1b2scbe0]

This is the output Watt Meter. It measures the draw from the batteries.
[youtube:1b2scbe0]zEj-BRkcHDo[/youtube:1b2scbe0]

These meters measure 7 DC values:
Amp-Hours
Watt-hours
Amps
Watts
Peak Amps
Minimum Voltage

[markopolo]

A few photos of the Watt Meters:

Top meter measures power in. Bottom meter measures power out.


Watt Hours


Minimum volts


Peak Watts


Amps in (top meter)


Amp hours out

[markopolo]

Here are some Amp draws I noted tonight:

Propane detector: .03 amps (the propane detector is always on - subtract .03 amps from a numbers below for better accuracy)
Fantastic Fan: Low: .92 amps, Medium: 1.25 amps, High: 1.73 amps
LED lights:
1 bulb: .11 amps
2 bulbs: .19 amps
3 bulbs: .26 amps
4 bulbs: .34 amps
5 bulbs: .40 amps
6 bulbs: .47 amps
Inverter on: .50 amps or .63 amps with microwave over clock on
110v Fluorescent light fixture on inverter: 1.2 amps

Plugged into grid power: 0 amps out (all current supplied by converter) This might be different if you have an inverter/charger rather than a converter/charger. Maybe someone with an inverter/charger will let us know.

[markopolo]

Here's another meter that might be a better choice:

http://www.ebay.com/itm/170869014075
http://www.ebay.com/itm/180957166631
http://www.ebay.com/itm/170901497030

Looks to be much easier to read.
It measures both forward and reverse current. (my guess is that it will show "net" current)
It has a proper sized 100 amp shunt.

The seller sent me some pdf files that I will read through.

--------------------------------------------
The meters I have are hard to see because:
1. I mounted them near the floor
2. They don't have a backlight

[markopolo]

I you just want a ammeter without having to install a shunt then this one with a Honeywell hall effect sensor should do it:
http://www.ebay.ca/itm/0-56-3-Red-LE...m=110933738306

[markopolo]

I had my van out of the garage yesterday to wash it so I had a chance to observe the charge from the solar panels (120 watts of panels). The Sept 2, 2012 around 4pm sun looked to be at an angle of approx 45 degrees.

For the short test I ran the fantastic fan and observed:
Amp hours in: .318
Amp hours out: .313

3.49 amps in peak.

What was interesting was that the charge came in stages. It wasn't steady. It would charge and then stop for a while and then charge again. When it was charging it supplied all the current the fan needed. When it wasn't charging the fan drew current from the battery. I would have expected to see a steady output from the solar controller.

I need to learn more about this to see if there is a problem with my solar controller or if it is normal for it to perform this way. My batteries were fully charged at the start of the test. Charging seemed to begin when the voltage dropped to around 12.85v. It would get back up over 13v and then stop. The process would repeat like that.

[Armchair RVer]

That is impressive, but unfortunately, way over my head. I can't see how you can measure wattage in the "Switch down" position when most of the current bypasses the wattmeters??

I have played with solar this summer a bit and found that voltage from the cells was quite stable. So really all I needed to know is the electric current to determine the wattage. But mine was an easy setup.

The only problem with ampmeters is that I kept blowing up the fuses on them. It doesn't take much... like turn the rotating dial on the ampmeter the wrong direction, and over do the current, and there the fuse goes..

[markopolo]

Originally Posted by Armchair RVer

........ I can't see how you can measure wattage in the "Switch down" position when most of the current bypasses the wattmeters?? ....................

You understand it correctly. When that large switch is in the down position the meters are not measuring. That large switch has to be open or in the up position to get accurate measurements.

The large switch is a bypass. The meters have small wires (14 gauge I think). I have 2 gauge wire running to and from the large switch. I put the bypass in so I can still run heavy current loads off my inverter and not burn up the meters. By heavy current loads I mean items like the microwave oven at maybe 90 amps. I'm not comfortable pushing that much current through the meters and the 14 gauge wire. The large switch lets me route the current around the meters or through the meters - I can choose what I want.

[Armchair RVer]

Thanks for the explanation. Looks like you've got all angles covered then.