MMW is an acronym for MilliLiter(s) per Minute per Watt.
MMW is meant to measure the efficiency of any given electrolyzer technology; particularly electrolyzers designed for on-board vehicle use. The idea is to know the relationship of the volume of BG being produced (milli-liters) for each watt-minute of work (volume of electrical energy).
MMW came into the public domain (I haven’t tracked down the originator) during the explosion of on-board electrolyzer experimentation that happened during 2008. The originator popularized the measurement even though there was already (for decades) an electrolyzer efficiency standard in place and accepted worldwide by the scientific community.
The ‘official’ standard for electrolyzer efficiency is Watt-hour(s) per Liter (Wh/L). Watt-hours are a measurement of work, so this measurement gives the actual amount of electrical energy it took to make 1 liter of BG.
So, an on-board electrolyzer (like the Mighty Mite version of the HyZor technology) that measures 30 seconds to fill a 1,000 mL volume, using a steady 13.8 VDC and 8.5 ADC would calculate:
Given:
13.8 VDC * 8.5 ADC = 117.3 watts30 seconds to fill 1,000 mL = 120 liters/hr117.3 watts * 1 hr = 117.3 Wh
Results:
117.3 Wh / 120 L/hr = 0.9775 Wh/L (for Wh/L smaller is better)
2000 mL / 1 minute / 117.3 watts = 17.05 MMW (for MMW larger is better)
Here are some very good MMW spreadsheets you can download so you can know the efficiency of your experiments (click) (click).Here’s a nice simple online MMW calculator (click).
The key factor you need to consider is properly taking measurements to assure an accurate result.
For ‘pretty good’ at home testing, we start with making a gas Volume Testing Apparatus (click)
My testing protocol is:1. Get the electrolyzer producing gas under the conditions that it will be tested (pressure, temperature, etc.) You want ‘steady state’ conditions.
2. Note the amperage and the voltage at the time of the test.
3. Switch the output of the electrolyzer to the VTA; starting a stopwatch at that same instant.
4. Watch the volume markings on the VTA and stop the stopwatch at a chosen volume.
Now I have amperage, voltage, volume and time. Simply calculate for Wh/L and/or MMW.Here’s a nice simple online MMW calculator (click).
NOTE: For highest accuracy make sure the liquid level inside the bottle is even with the liquid level outside the bottle.
This VTA only works when testing at ‘steady state’ pressure, because if the electrolyzer loses pressure as it is tested, you’ll get a false volume as the ‘stored’ gas expands to ambient pressure. Most people simply get the electrolyzer operating with the BG outputting to atmosphere and then plug the electrolyzer output into the VTA when starting the stopwatch.My VTA is slightly different than most in that I counterbalance the weight of the testing bottle. When measuring without counterbalance, I lift the bottle to keep the liquid level inside the bottle even with the liquid on the outside of the bottle. This VTA does a pretty good job of keeping the liquid levels even, so your volume measurement will be accurate. I use this apparatus because I’m often testing by myself and I don’t have three hands :)It’s also important to note that the temperature of the water and any impurities in the water can affect the ‘reading’. I use pure water at ambient temperature (about 70°F). If my electrolyzer is hot, I bubble the output gas through water to bring it’s temperature to around 70°F. This eliminates inaccuracies that would be caused by steam volume in the output gas.
For absolute accuracy (not generally needed unless comparing results to other electrolyzers) the ambient air pressure needs to be factored in, to correct the gas volume to US-STP.