Are specific gravity readings highly accurate?

softdown
softdown Solar Expert Posts: 3,896 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
For well over two decades, I have been a professional aquarium specialist. The tool is measures the SG of salt water is almost identical to the tool used to measure the SG of a battery.

Having bought, and sold, dozens of these SG tools, I will testify that the overwhelming majority have been off by a fairly significant amount. For example, the saltwater has a SG of 1.023. These flotation devices will generally give a readout between 1.021 and 1.025. Doesn't sound like much but it is a very significant difference.

Battery SG measurement tools costs a lot more than saltwater SG measurement tools. Obviously they use different materials to handle the corrosive properties of battery acid. Let us *hope* that quality control measures are far higher. Some manufacturers care. Many do not. Especially in todays environment of cost cutting and fancy boxes housing good looking, cheap crap.

At any rate and irregardless of the initial quality of your own SG gauge. It needs to be rinsed with very clean water ~ three times after each usage.
First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
· Share on Twitter

Comments

  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #2
    I was always frustrated with the several glass hydrometers that I have used.  I always felt that the readings were difficult to reproduce.  No doubt caused by stickiness.  I was always careful to rinse them with distilled water after use, but I could measure a cell 3 times and get three different readings.

    I currently use a Hydrovolt hydrometer and find it to be quite reproducible and it has built in temperature compensation. 

    I have used refractometers on a few occasions and found the readings to be quite reproducible.  The ones I used had built in temperature compensation.  

    Most of the professional installers that I know carry refractometers in their tool boxes.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
    · Share on Twitter
  • Ralph Day
    Ralph Day Solar Expert Posts: 1,022 ✭✭✭✭
    #3
    I've tried a refractometer but it didn't work well.  "Zero-ing" it with distilled water resulted in readings way off.  Zero-ed with known acid sg and it worked ok.

    Hydrovolt I found too cumbersome compared to my good bulb hydrometer.  The bulb squeeze on the HV was just too much over 24 cells, and the original tip tube was too short for my fill wells.  Back to the glass bulb type.  I stick to what I know.

    Ralph
    · Share on Twitter
  • softdown
    softdown Solar Expert Posts: 3,896 ✭✭✭✭
    #4
    Hydrometers will be the go to measurement device for most. But I suspect that we may need to realize that the measurements may  be off by a bit. Much like thermometers....almost all give a slightly different reading.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
    · Share on Twitter
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #5
    Ralph Day said:
    I've tried a refractometer but it didn't work well.  "Zero-ing" it with distilled water resulted in readings way off.  Zero-ed with known acid sg and it worked ok.
    Both refractometers and hydrometers should be calibrated with electrolyte of known SG, and the calibration solution should be in the range of SG that you wish to measure. 

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
    · Share on Twitter
  • softdown
    softdown Solar Expert Posts: 3,896 ✭✭✭✭
    #6
    Once bought a very expensive refractometer. It never worked once. People wonder why I'm cheap.

    Ralph Day said:
    I've tried a refractometer but it didn't work well.  "Zero-ing" it with distilled water resulted in readings way off.  Zero-ed with known acid sg and it worked ok.

    Hydrovolt I found too cumbersome compared to my good bulb hydrometer.  The bulb squeeze on the HV was just too much over 24 cells, and the original tip tube was too short for my fill wells.  Back to the glass bulb type.  I stick to what I know.

    Ralph

    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
    · Share on Twitter

Categories