DIY Lee Hart's zener lamp Battery Management System

[Leslie]

Ok I was looking at my batts as they were charging and I saw some disturbing voltages on one of the batteries.

I called up Rod from EV-power Australia to order some stuff and asked him about an SLA BMS for my batts.


He mentioned some stuff about installing over each battery terminal 2 zener diodes to = 14.3 volts in opposite polarity and a lamp to take the load off.

Now im looking around google and I cant find what wattage zener would do.  The only ones I can get ATM are 1 watt.  This seems pretty poor IMO so what do I install? 2 * 1 watt zeners in parallel and a 500 milliamp bulb?

Will a 1 watt shunt away about 2 volts on a 2.2 amp charger?


Updated:[/color]

6.8V 1N4736 5 Watt Zener Diodes 
6.3V 1N4737 5 Watt Zener Diodes
2.4 volt 3 watt lamp

Will update to the final



          zen    lamp
     |--[|<]--|''|----|
0v n_____________n 16+v unbalanced, 14.3 volts zener voltage break down.
    |                      | 
    |______________|

Im working out I need 4 watts at least.

Hmm but the lamp takes the heat off the zener...



Thanx in advanced.

[Leslie]

I found a tutorial in pdf compressed and condensed it. Here goes!
Ill tinker with the values whe I get some feed back or when I get the bits tomorrow and test it....
This is set up for my 18ah sla's and 2 amp charger.

Things you need.

Updated:

6.8V  5 Watt Zener Diodes 
6.3V 5 Watt Zener Diodes
2.4 volt 3 watt lamp
Resistor to be decided.



In this tutorial this guy used a pr2 bulb, these come in diferent sizes looking at the data charts the 2 zeners break reverse at 5v and 4v = 9 v so 12 volts is going to fit the job, and he adds a resistor in parallel incase the bulb blows im thinking...

Solder the resistor in parallel to the bulb.





Then we get a zener and hook it to the positive ring terminal with the striped end pointing toward the ring to block the current.






On the other negative terminal keep the polarity the same and face the the striped end away from the negative terminal.




Solder the resistor end to the either the positive or negative terminal with bulb in parallel .






Nice job, matey gets an A+ on ebay





Works like a charm.




When the charging battery reaches 14.3 volts the zeners break down creating a shunt circuit and draws around 9volts into the bulb and resistor lighting it up and burning off the the extra current. The result is a voltage drop across the unbalanced battery while still allowing 14.3 volt to get through to the next battery and so on untill the charger reaches it full potential.

Can anyone here elborate on this design and improve what I am saying here please assist me in getting this perfect.

Les

[Leslie]

It works and good too.  I got my hands dirty and tired a few things out.

The PDF tutorial lacked all the values of the zeners PR2 globes (what ever they are) Im thinking it means 2 volts.

Ok I went to the electronics store and got the tinker stuff, Welll after I fried a few one watt zeners I used the last 5 of each in parallel. 

I got my test rig charging and saw the one reading 16.2 volts.  I whacked my zeners on reversed and put a few different lamps on the best one was the 2.5 volt 3 watt and the zenner became hot and the battery voltage droped to 14.55 volts. the lamp lit up dim and died out and heat was burning off and almost got to hot to hold.

Im thinking id use 6x10v 1 watt zeners in parallel  in series to  6x3.3v or 6x3.6v zenners in parallel to get it down to 14.3 14.4 volts and ill keep using the 2.4 volt globe as I don't want these tio blow at any stage and don't care about if they stay lit up... 
They will with the smaller value zener I gather.

Im using a 2.2 amp charger on 18 amp hour batteries that say intitial charge cycle between 14.3 max 14.5. and my little BMS system is kicking the volts like I want them...

I'll put these zeners on a blank PCB board and wire it up all pro into a box the connects to my power leads.

I would supply pics but I had no hands free to take photos...

Ill finish this.

Sucess

[Leslie]

Ok. more.

I figured that the 7.5v and 6.8v worked great. 14.55v full charge is better than 16.5v.

Other people that used this design ive read use much bigger chargers and 12 sla's in series with bigger globes.  You got to think 12 batteries in series is going to put some batteries out quite a bit...  I wrote this all out wrong to begin with as I'm learning this simple circuit.

Using 6X7.5v 1 watt and 6X6.8volt zeners and a 3 watt globe in between I figure is is where im burning off the extra current.  Because Im only using 3X12 volt SLa's the unbalance is small so the need for larger globes is overkill and the larger globes didnt do what I wanted.

Les.

[Leslie]

There is a thread over at ES regarding a Zener resistor BMS thread.

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=6604&p=99906&hilit=zener#p99906

there isnt much positive feeback.  Makes slow charging is my only concern in all that.  It takes my SLA's 4.5 hours to charge max 5 hours if the bike does one trip a day which is more than often.   SLA's when not discharged  below 45% can last a very long time.  One old fella I got speaking to said his sons exon SLA's in his car did 12 years...  Take the stress off them, charge them with a charger rated a good half under the manufactures rating and make sure the battery can handle the current rate. (SLA 18ah +56 amps. ive seen the pull 100 amps peak) charge the batteries with a simple zener balance system, fuse it and Im looking for the the long hall. Hopfully least 3 years +.

I think its more to do with how this works and not how it doesnt. I watch the charge phase voltage go up and down on the other batteries that werent shut off and this battery remained pretty flat some times it woud go up to 14.68 and down to 14.55 for a little bit.  The zenner doesnt alow the full signal amplitude through, so this is not a bonus it just shuts/shunts the charge.  Well while this happens the other batteires get time to push the the zener voltage back down on the shunted battery, a lot faster than people imagine too, the zener shuts off the charger signal, however at 14.55 volts, a higher voltage potential than float battery phase or just resting for that matter.  This acts as though its sitting in parallel with a battery 14.55v (in this design), the plates must absorbe the voltage in a form, speeding the charge up the process..  Now this again, even if there is a 'runt' cell as always, the overvolt inadvertently, is cut to that runt cell  regardless and the battery gets a breather so the cells have a chance to balance themselves.

My charge max cycle voltage from my chargers is 43.5 thats 14.5 per batery on the dot, when unbalanced at 16.5volts it seems, instead of that runt cell copping the two more volts (poor lil runt), can anyone tell me which cell in the in the batteriy is does get hammered when the zener is shunting the 2.2 volts im measuing here with no (oh dear) load resistance, 2.8v no load? 

[Lanchon]

the problem with this balancing circuit is that 12V lead-acid batts are really 6x 2V cells in series. so I don't know why all six cells in a batt would unbalance "in tandem" with respect to other cells. (of course I'm assuming you're following standard recommendations and stringing only same type batts with a similar usage history.)

cell balancers are typically not used with lead-acid because these cells can tolerate moderate overcharge (not the case of lithium). after a normal charge, the batts can be "boiled" a bit to balance the cells by continuing the charge. in overcharged cells electrolysis turns water into O2 and H2 gases (explosive mix!), while undercharged cells keep charging and balance up. I believe SLAs have catalyzers that recombine most of the gas back into the electrolyte, as long as boiling is done slowly. wet ones you have to replenish with distilled water.

[Leslie]

the problem with this balancing circuit is that 12V lead-acid batts are really 6x 2V cells in series. so I don't know why all six cells in a batt would unbalance "in tandem" with respect to other cells. (of course I'm assuming you're following standard recommendations and stringing only same type batts with a similar usage history.)

Cheers.

I kept looking at my bulb voltage thinking 2.5 volts where have I seen this before. 

Im going to tinker with the ultracaps I have sitting here to see if I can inuct some regen to help defeat voltage slump in SLA's.