Thursday, March 13, 2008

Teaser for 9W2ALT and 9W2LYZ...

Here is the startup display of your voltmeters...
They just underwent 7 hours of burn-in test last night...
No problem...
On the topic of battery monitoring, note below is extracted from Wikipedia...

These are general voltage ranges for six-cell lead-acid batteries:

  • Open-circuit (quiescent) at full charge: 12.6 V to 12.8 V (2.10-2.13V per cell)
  • Open-circuit at full discharge: 11.8 V to 12.0 V
  • Loaded at full discharge: 10.5 V.
  • Continuous-preservation (float) charging: 13.8 V for gelled electrolyte; 13.5 V for AGM (absorbed glass mat) and 13.4 V for flooded
  1. All voltages are at 20 °C, and must be adjusted -0.022V/°C for temperature changes.
  2. Float voltage recommendations vary, according to the manufacturer's recommendation.
  3. Precise (±0.05 V) float voltage is critical to longevity; too low (sulfation) is almost as bad as too high (corrosion and electrolyte loss)
  • Typical (daily) charging: 14.2 V to 14.5 V (depending on manufacturer's recommendation)
  • Equalization charging (for flooded lead acids): 15 V for no more than 2 hours. Battery temperature must be monitored.
  • Gassing threshold: 14.4 V
  • After full charge the terminal voltage will drop quickly to 13.2 V and then slowly to 12.6 V.
For more information, click here


9W2RYZ said...

Hey bro,

How much you selling? I have a friend who might be interested to get one.

I also have a few questions:

1) I suppose it is not important for a car volt meter, but I'd like to know (roughly) the input impedance of the meter.

2) Is the voltage input same as the power supply? If same, do you need to connect it after the ignition switch?

3) Can this meter monitor the voltage trend over the last 30 minutes? Meaning, taking (and storing) a voltage sample every, say, 3 minutes, and compare the latest 10 results to indicate if the voltage has been rising, constant or dropping. (I'd be really interested in this feature.)


9W2BSR said...

Price around RM60...
1. The input impedance is roughly 25k ohms. Can be increased if needed... It feeds into a voltage divider...
2. Yes, the voltage input is the power supply.
3. Trending can be done if needed... There's still room for codes inside.

9W2BSR said...

Btw, since the unit take power from the car battery, I suggest wiring it to accessories power line (similar to Radio, cigarette lighter, etc). During ignition, the power to the accessories will be cut thus preventing dangerous spikes from effecting the accessories and this unit.

That is how it's wired in my Sorento now... connected to the cigarette lighter...

9W2RYZ said...

OK. The impedance is high enough.

If you can provide voltage trend, can you also provide display off, so that the meter can be connected directly to the battery full-time (to monitor trend) but display is switched off when the ignition is off to lower the consumption. We can take care of power spikes with those ferrite rings.

Another good feature is to display lowest and highest voltage within the same 30 minutes trend. These features may help us determine if the battery condition is deteriorating and a battery change is imminent.

Bolehkah? Now I'm getting more interested.


9W2BSR said...

Display off function can be made... just need two resistors and another sense wire...

The min and max will need a switch to toggle between readings... need bigger casing already... no more space in current casing :(

Battery deterioration is not overnight... Daily check of the voltage will give you indication of battery condition already...

For info, based on last few days, the behavior are as follows:
1. Voltage in morning is around 11.9-12.1V (accessories on).
2. After ignition it's about 14.5V, constant current charging.
3. After about 15 minutes of driving, it's about 13.5V-13.8V, top up charging.
4. During driving it vary about 0.5V.

The features you mentioned are easy to implement, just need additional components and some more programming :)

9W2RYZ said...

No need to add components. Just display the readings this way:

Display current voltage for 5 to 8 secs.
Flash Lowest voltage for 2 secs.
Display trend: _-* (for rising), --- (constant), *-_ (dropping) - for 2 secs. (* for segment a)
Flash Highest voltage for 2 secs

Yes, battery deterioration is not overnight. But it is difficult to monitor with just a simple voltage reading. The good guide will be the voltage trend in the first 30 minutes of charging when you start driving around in the morning, and the 30 minutes after you switch off the engine.

One more thing about capturing the trend. When displaying the current trend, please exclude the latest 2 readings. This means that the trend should be 3 to 6 mins delayed. This is to ensure that when you start your car in the morning, the immediate charging do not affect the trend reading. Also, if the voltage varies less than 0.3V in 8 readings, voltage should be regarded as constant.

For displaying highest and lowest voltages, 30 mins time span is not good enough - coz if you drive around longer than 30 mins, the lowest voltage reading become meaningless. Maybe 24 hrs data taken at 30 mins interval? What do you think?

So modifications are in the programming only, except for display off feature.


9W2BSR said...

May be you can enlighten me more... based on the voltage readings I show above, after 30 minutes, result will be as approximately as follows:

Lowest Value: 11.9V (Engine Off)
Highest Value: 14.4V (Engine Started) @ T0
Current Value: 13.8V (End of Journey) @ T30
Trend = dropping?

Likely scenario after engine off:
Highest Value: 14.4V (when engine first started)
Lowest Value: 12.5V (estimated, after 30 mins)
Current Value: 12.5V (both current value and lowest value will be the same).
Trend = dropping too?

How would I be 'better' informed through these?

9W2RYZ said...

Wah! Cepatnya response.

OK. My initial description was confusing. Sorry.

The Highest and lowest reading is NOT related to the trend. Highest and lowest values are taken over 24 hours. The trend is taken over last 30 minutes.
Remember the meter is connected full-time to the battery. Only display comes on when key is switch to ACC.

However, Hi and Lo readings are also a good indicator of a weak battery.

I'll email you a graph to describe the trends.


9W2RYZ said...

On second thoughts, based on your data which quite conforms to my observation on my car, and also to make your programming easier, I think a shorter period for trend monitoring is more meaningful.

So I suggest you store 4 readings taken at a 3-minute interval, and use the previous 3 readings for display. This means the trend is monitored over the last 9 - 12 minutes. In this case, a voltage difference of less than 0.2V should be treated as constant.


9W2BSR said...

New firmware done... display 'off' when voltage drop below 13.0V, i.e., ignition off... checkout new blog entry on the matter...

9W2RYZ said...

Eh! Tak boleh.

What if you want to check the voltage reading without starting the engine? Just turn the key to ACC should turn on the display.

9W2BSR said...

Aiyaa... read the blog details la... :-)
The display will blink for 0.5s every 3s when voltage is below 13.0V so it doesn't draw more current than normal operations... Thus, you can still check the voltage with ignition off...

BTW, the unit takes about 50mA during normal operation thus during 'off' blinking, it will just take less than 10mA... negligible by car battery capacity...

9W2BSR said...

BTW, with the revised operation mode, no modification required to the circuit...just firmware updates...

9W2RYZ said...

...The display will blink for 0.5s every 3s when voltage is below 13.0V...

This on time of 0.5s is only to display current voltage, isn't it? What about other Hi, Lo, and Trend readings?

I still prefer adding a sense wire to the ACC provided you have a free input port available.