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Zener Regulator (Double)


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After I installed a Victron 702 battery monitor I became aware that my battery bank was out of kilter by sometimes more than 1 V. In researching a remedy I came across this YouTube post.

 

and

 

https://www.youtube.com/watch?v=H5Z8pBE0HlU.

 

Dockarl then made the following videos for me 

 

 

 

 

The following document is what I based my Zeners on (http://www.evdl.org/pages/hartregs.html).

 

The Zener diodes give off a fair amount of heat and traditionally the battery posts are used as heatsinks. Since my batteries are in a box and I cannot see the bottom two batteries I wanted to do something different.

 

A computer CPU heat sink was just the thing, but the space between the fins was too small so I drilled out every second fin and used silicon to secure the Zener diodes. My batteries are 260 Ah so I decided to double up and have two Zeners per battery. The fan means I now need a power source so I plan to link up an Arduino, build 4 voltage dividers, and log on my computer individual battery voltages.

 

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Chris, have you measured and compared your zeners before assembling everything. I needed 32 zeners for my 16 batteries and ordered 60 zeners. I then measured each of them on the work-bench and their values were all over the show. I got voltage differences of up to about -0.1V and +0.3V at the same constant current - if you use say two of the -0.1V zeners for one battery balancer and two of the +0.3V zeners for another battery balancer, you might get a "balanced" voltage with a difference of up to 0.8V between the two batteries. I still have to mix and match my zeners to get pairs with similar clamp voltages at a specific current. I've also measured and grouped my 3.9ohm 5% resistors. 

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Hi Chris,

 

May I ask what values you used on the zeners? 6.2 or 6.8V or what combination?

 

Hi Edmund welcome to the forum. I used a 6.2V and a 6.8V in series.

 

 

Chris, have you measured and compared your zeners before assembling everything. I needed 32 zeners for my 16 batteries and ordered 60 zeners. I then measured each of them on the work-bench and their values were all over the show. I got voltage differences of up to about -0.1V and +0.3V at the same constant current - if you use say two of the -0.1V zeners for one battery balancer and two of the +0.3V zeners for another battery balancer, you might get a "balanced" voltage with a difference of up to 0.8V between the two batteries. I still have to mix and match my zeners to get pairs with similar clamp voltages at a specific current. I've also measured and grouped my 3.9ohm 5% resistors. 

 

Hi SuperDIY

 

I bought 30 6.2V Zeners and 30 6.8V Zeners and measured them on variable power supply. The one I have flicks between constant current and constant voltage and I was able to reasonably accurately determine avalanche voltage. I had a whole lot that measured the same avalanche voltage. I have just measured across the Zeners now and they range from 12.96 through to 13.08 V

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Hi Chris,

Thanks. I current have 2 x 6.8v zeners and cannot see much happening. That being said after I corrected the installers battery connection it seems to be in balance throughout the charge and discharge cycle.

 

Hi Edmund

 

My Zeners' LEDs only light up at about 14.5V. My Bulk charging is 56.4V (14.1V) below gassing voltage at 25oC so I am unlikely to see them glow unless there is a problem. I tested them against a variable power supply and they light up like a Xmas tree at 15V. My Zeners are heating up - the heatsink is normally cool to the touch with the fan on and now there is only a small difference between it and my hand's temperature. So although I cannot notice it from the LEDs there is a flow of current.

 

Dockarl the Aussie whose post I have been following says it takes several cycles before the batteries become balanced.

 

Chris 

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post-822-0-68584700-1439388020_thumb.jpg

 

I suppose the proof of the pudding is in the eating. I was in the shearing shed most of today but came in for a cup of coffee mid afternoon. I have never seen no difference in the midpoint voltage - perhaps the Zeners work after all. The sun has not shone brightly all day so definitely not a definitive test.

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  • 2 weeks later...

Just an update. In spite of the Zeners I continued to battle with my batteries being out off balance late in absorb. Once into float things would even out. A large intermittent draw would more often than not rapidly cause the battery bank to be unbalanced. When I made my cables I did not have gas for my blowtorch and could not solder the lugs onto the cable. All I could do was crimp them. I wondered whether this was having an effect and thought I might have a dry joint. I earlier this week took all the cables to the workshop and soldered the lugs. It seemed to make no difference. Zeners need several cycles to balance a set of batteries.Today has been rainy and overcast and although we never had 20 -30A from the panels we have had enough sunlight to bring us up to 96% SOC  without a midpoint voltage deviation of greater than 0.6%.

 

Battery voltage has hovered around 54V (float most of the morning).  I would have expected the voltage to be closer to 56V by now. Any ideas what is happening today with my system?  

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