Amp-hour meter

[Otto]

I purchased the Doc Wattson meter and I am confused as to how to interprut the amp hours it is displaying.  I must have misunderstood something along the way, because I thought an amphour meter read zero when your batteries were fully charged and would display negative numbers as the batteries were being drawn down. As an example if my batteries were capable of 500 amp hours at full charge and the meter read -100ah I now know I have 400 amp hours left in the batteries. The Doc Wattson does not display negative numbers as the batteries are being drawn down but is displaying amp hours.  Assuming the displayed amp hours are what has been drawn from the batteries, shouldn't the meter reset as the batteries are being replenished/charged?  I hope this made sense.  Please enlighten me.

Otto

[Volvo farmer]

I don't have one of these but it is apparently similar to the "Watts up" monitor. Watts up says "Easilly reset data via the external pushbutton switch." Do you have an external pushbutton switch?

What you seem to be seeking are the features in the Trimetric 2020. It costs three times more than the Doc Wattson, but counts negative amp-hours and resets itself to zero once the battery voltage reaches a user-defined point. I use the crap out of my Trimetric. I honestly wonder if I'm going to wear out the buttons on the thing.

Here's a feature I really like for an off-grid system. I have a Mate on my Outback inverter which tells me battery voltage, so I set the Trimetric to display instantaneous amps. So at a glance, I see volts AND amps (plus or minus). I highly recommend this setup because it provides way more information than just volts OR amps. A couple button pushes gets me amp-hour data, and for the wife, she can see the remaining battery capacity in percentage.  

My neighbors leave their Trimetric on volts all the time and I think that value can mislead a person. I came home today after a mostly cloudy day but an hour or so of sun in the afternoon. My battery voltage was 26.2 (24V system). It looks all good until I see that I'm still 85Ahr down from the day before. I never got to absorb voltage, I sure didn't hold absorb voltage for two hours like I want to, or my MX60 would have told me the float time minutes.

So maybe Doc Wattson is a manual meter and you reset it yourself when you know for sure batteries are full, just know that it only counts negative amp-hours and reverse your thinking?

[snowcrow]

  Otto, even if you buy a second "Doc Wattson" you will still be ahead money wise.  

  I have one for solar, one for wind, and one for the load center.  My Xantrex C-35 controls and meters a diversion load.  The four meters tell me a lot about the health of my system and where my money for future expansion would be best spent, wind, solar, or storage.

  One great thing about the "Doc Wattson" is the 3 wire hook-up, which meters the negative pole, allowing for higher current metering, and allowing you to use one push-button switch to reset all meters at once on the positive poles.

Blessings, Snow Crow

[Otto]

Snow Crow thanks for the reply.  Is there a way I can use the Doc Wattson as a fuel gage of the battery charge/how many amp hours I have left in them?

Thanks,

Otto

[snowcrow]

  Otto, you will need to have at least two meters, one for incoming power sources, and one for outgoing power to loads, including dump load!  You just subtract outgoing power for the incoming power to get the approximate amp-hours stored.  The true storage capacity of your batteries will depend on temperature, age of the batteries, and rate of discharge.  It's not as simple as "power in" equals "power out".

  This are some links that maybe of interest to you:

  http://otherpower.com/otherpower_battery.html

  http://otherpower.com/otherpower_battery_metering.html

  Here is another link to the manual that should give you a better idea of its uses:

  http://www.rc-electronics-usa.com/docs/wu100v2_user_manual.pdf

Blessings, Snow Crow

[Otto]

Snow Crow I am a little dense.  I have read these sites. Isn't there a meter that just measures how many amp hours I have in my battery bank?

Thanks again,

Otto

[snowcrow]

Otto, try this: http://stores.mavericksolar.com/Detail.bok?no=55

Blessings, Snow Crow

[Otto]

Thanks Snow Crow

Otto