- Projects -

These are some projects that might be helpful in conversions

From http://www.cameronsoftware.com/ev/EV_BatteryManagementSystems.html

Each battery has a regulator which consists of

• 2 - ring terminals, with hole for 5/16" bolt, and crimp for #6 wire
• 2 - 6.8v 5watt zener diodes
• 2 - #PR2 flashlight bulb

Solder a zener diode into each ring terminal where the wire normally goes. Solder a 6" piece of wire to the other end of the zener diode. Solder the flashlight bulb between the free ends of these two wires. Now you have the two zeners and flashlight bulb all wired in series.

Lee added on 8/09 - Since there are two zeners in series, and they have a 5% tolerance, I measure their actual zener voltage, and match them up in pairs with the same total. I have a bench power supply with knobs to set the voltage limit and current limit. I set the current limit to some value like 100ma, and set the voltage limit higher than the zener voltage (like 10v for a 6.8v zener). Connect the zener, and the power supply automatically supplies a fixed 100ma. Measure the voltage across each zener. Sort them into bins (6.5v 6.6v 6.7v 6.8v 6.9v 7.0v 7.1v). Use pairs that add up to the same total
6.5v + 7.1v = 13.6v
6.6v + 7.0v = 13.6v
6.7v + 6.9v = 13.6v
6.8v + 6.8v = 13.6v

Fill the space between the zener and ring terminal with epoxy glue. Likewise, dunk the bulb and its wires in epoxy glue. This makes everything waterproof and acid proof, and helps conduct heat. The zeners get their heatsinking from the large ring terminals and battery posts they are bolted to.

Lee wrote on 9/2/09 - On mine, the diodes are potted with a thermally conductive glue inside a "heavy duty" copper ring terminal. The ring terminal is bolted to the battery to act as a heatsink for the heat produced by the zener.

Put one of these circuits across every 12v battery. If the charging voltage exceeds about 13.6v, the zeners begin to conduct and the lamp lights. At about 15v, the lamp is fully lit and is bypassing about 0.5 amps.

Use a photocell to detect the light being produced. When any of these battery regulators lights, the photocell sees it and either switches the charger off, or to a low-current trickle charge or float voltage setting.

6 V Version -

Comments and an ansii schematic by Lee (5/06) -

I published the version for 6v batteries a year or so ago. Basically, I suggested the same parts (two 6.2v zener diodes), but with *two* #PR2 lamps. Each lamp has a zener in series. This makes two parallel paths, so it shunts twice the current -- 1 amp max instead of 0.5 amp max. This is more appropriate for >100 amphour batteries.

One zener and one lamp in series, wired across the 6v battery. Use two such regulators across each battery. Physically, you'd put one zener in the ring terminal on the + battery terminal, and the other zener in the ring terminal on the - battery terminal. Like this:

If the 6.8v zener lets the voltage get too high (gel cells, for instance) try a 6.2v instead.

You want a zener that draws negligible current when you aren't charging. The fully charged voltage for lead-acid is around 2.1v/cell, which is 6.3v for a 6v battery, 8.4v for an 8v battery, or 12.6v for a 12v battery.  AGMs tend to be a little higher, and floodeds can tolerate a little more. [The lamp]  provides a roughly constant current once the zeners start to conduct.

I used a pair because two 5w zeners are cheaper than a 10w zener. Also, I could put one in each battery terminal, to split the heat between them rather than concentrating it all at one point. Also (I never do anything for one reason :-) because the temperature coefficient of zeners around 7v is roughly zero.

The resistors act like just a backup system. Someday the bulb may burn out or get broken. The resistor means you don't lose *all* regulation.

Your charger has to be smart enough not to charge excessively. The charger has to be at a low current when the regulators begin working, and has to shut off after a relatively short time. You can do this "open loop" by arranging the charger so it automatically delivers low current for a short time. For example, a transformer-rectifier charger that is adjusted to deliver <1 amp at 2.5v/cell, and has a timer to turn itself off in 1-2 hours.

Or, you can do it "closed loop", where the light from the regulators commands the charger to cut back and turn off.

This is a parts list by Chris Zach, parts from Mouser

• 606-PR2, PR2 Chicago Miniature Incandescent Base Flange 2.38V .5A
• 526-1N5341B, 1N5341B NTE replacement Diodes/Rectifiers 6.2V 5W ZENER DIODE
• 610-CZ5342B, CZ5342B Central Semi Diodes - Zener 6.8V 5.0W
• 660-MF1/2DLT52R10R0F, MF1/2DLT52R10R0F KOA Speer 1/2Watt Metal Film Resistors 10ohms 1% 100PPM

And of course you need potting compound:

• 1 590-832-TC-450ML Epoxy Compound 1 1 0 $29.95

The smaller lugs are standard Home Depot 12-10 gauge yellow lugs; the smaller diode fits in them. For the larger one I used heavy-duty 6ga tinned eyelets, with a 5/16" bolt hole, from Waytek Wire, part# 36472.

Here is a link to a PDF that shows the steps in making the Zener regulator

I got these drawings of Mark Brueggemann's when I got my partially finished S-10

Side view, showing the gas lift attachment and the fabricated frame that the bed sits on.

This shows fabricated frame that the bed sits on and the pivot hinge details

A 24vdc supply is plenty for rejuvenating a 12v battery. If 24v won't bring it back, give up. "He's dead, Jim".

A light bulb works well as a current limiter, in case there's a shorted cell. The initial current will probably be quite low, but it will g-r-a-d-u-a-l-l-y rise as the battery moves away from 100% dead. Note that it may take DAYS for the current to stop rising.

Once the current stops rising, remove this high-voltage current-limited charger. Wait a while, and check the open circuit battery voltage. If it's around 12v or more, it's OK -- continue charging with a normal 12v charger. If it hasn't come up to at least 12v, you probably have a shorted cell -- the battery is shot.

Lee Hart - EVList, 6/07/06

Hello everybody,

About 6 months ago I wrote an article here (Battery undervoltage warning). The idea was that I would be able to avoid my nemesis, unequalised batteries (explained here), and have early warning of bad connections like the one which caused this terminal failure in my car. Argh!

The battery monitor was fairly successful but only gave a crude qualitative measurement of voltage drop. I have been looking for something better. Something with which I can see the actual voltage each battery is at.

When I saw the battery monitor on Jim Fell’s Seicento I had to have one. It’s based on the robust LM3914 LED driver IC.

The circuit I found and adapted can be found here. National Semiconductors have kindly provided an example circuit and some very good explanation.

I adapted this circuit to show 10 lights for 6.37V and above and no lights for 5.75V and below, with the rest of lights showing about 0.6V intervals. Each interval loosely approximates to 10% DoD (Depth of Discharge). Here’s the schematic:

Here’s a table which shows number of lights shown against voltage and State of charge (100- DoD):

1. 5.75V ~10%
2. 5.82V ~20%
3. 5.89V ~30%
4. 5.96V ~40%
5. 6.03V ~50%
6. 6.09V ~60%
7. 6.16V ~70%
8. 6.23V ~80%
9. 6.30V ~90%
10. 6.37V 100% upwards

The LM3914 has 2 modes: “bar” where it will show all of the lights up to a certain light and “dot” where it will only show one (or occasionally 2 lights at a time). I started off using bar mode but I found this too bright and distracting – it lit up the whole car. Lighting up all those LEDs also drew a higher current and generally read lower due to the associated voltage drop.

You’ll see that I have designed this circuit for 6V Flooded lead acid batteries. For those of you running 8 or 12V you want to replace Rx with 33K or 56K respectively. I tested this at 12V with 56K and it works just fine.

For each meter you’ll need these components:

LM3914
10 DIL bargraph display
10 uF electrolytic capacitor
100R resistor
1k resisitor
270R resistor
10K resistor
22K resistor (for the 6V version)
200R precision cermet trimmer
500R precision cermet trimmer
IN4001 silicon rectifier diode or similar.
a piece of stripboard 10 holes x 16 holes (strips run along the 16 hole side)

All resistors should ideally be 1% or 2% tolerance.

The electrolytic capacitor needs to be very small and short if you want to mount all the boards together as shown below.

Tools required:

Small soldering iron and solder
Adjustable power supply (5.5 – 6.5V for 6v batteries)
Digital multimeter

If you have made the circuits tidily you should be able to glue the LED modules together and mount the whole thing on another stripboard.

Now to put it in the car.

I have left out all of the relays I used in the original battery monitor and the unit is now permanently on. I measured current usage and found that if you are using “bar” mode with all the LEDs on, you can expect to draw about 100mA per meter at 6V, probably about half that at 12V. If you use “dot” mode then you’ll draw about 10mA per meter. Certainly for my battery pack this is a very small loss.

I am so much more confident in my battery pack now that I can see what each individual battery is doing. I am sure that it’ll make the batteries last longer because I’ll be able to know about a discharged battery before I cause a cell reversal or over gassing.

That’s all for now! Step by step stripboard instructions coming up in Part 2.

James May in the UK

http://www.evconvert.com/article/led-bargraph-battery-monitor

Solectric S-10

When I was thinking about my conversion I really thought that the Solectric S-10 configuration was very well done.

They had 2 motors, 2 controllers and the battery pack all rear of the cab. The bed tilted up at almost 90 degrees.

Here you can see the rear of the S-10 with the bed tilted up, the 2 motors with the drive shafts facing to the rear. The rectangular aluminum box that they are bolted to has a rubber drive belt which in turn connects to the drive shaft of the rear end. The other end of the tail end of the motors connected to the cross member. You can see that the drive shaft has 2 universal joints to permit it to flex with the up and down of the axle.

Here is a view of the motors from the bottom rear of the truck. It looks like a different truck, cleaner.

You can also see that that there are 6 leaf springs. My US Electric S-10 also has 5 springs. As manufactured by GM it had a GVWR of 4800 Lbs, but US Electric added another leaf to make the GVWR of 5600 Lbs. So maybe the Solectric also has a GVWR of 5600 lbs.