Archive of Lee's Wiser Moments

In my meanderings in the EV space, I have met two men who have what I would refer to as 'guru' status. One is a mechanical guru, a practical mechanic with real world experience. The other - well, the other is Lee, and this is his page.

This is where I stick postings and emails from Lee that I think I, and others, can benefit from. I have obtained Lee's permission to do this (I think) so hopefully I won't be being sued any time soon.

Anyway, no words below are mine. They are the words of Lee Hart, EV guru.


Lee on Battery Maintenance

Let's anthromorphize a bit, and consider lead-acid batteries as alive;
like the family dog.

1. They need exercise; it's good for them. You get the longest life
   when they are worked to about 50% of their capacity at moderate
loads.
   After they have been loafing for weeks, you will notice a distinct
   improvement just from giving them moderate exercise. 

2. But don't work 'em till they drop! If you drive an EV until it
   barely moves, the batteries are having a near-death experience!
   This is outright battricide, and a leading cause of early death.

3. They need to be be fed regularly (charged). Feed as soon as possible
   after a workout; they don't like to sit around starving after use.
   Batteries left sitting for days in an undercharged state develop a
   condition called sulfation.

4. Don't overfeed, or they get fat and have cumulative health problems
   and so die early. Chronic overcharging is a major cause of early
   death.

5. Don't underfeed, or they can starve to death. Chronic underfeeding
   also leads to a weak sickly battery and an early death.

6. Batteries can sit unused for months (hibernate) without needing to
   be fed. You don't need to put them on a trickle charger; just be
   sure to feed them occasionally so they stay near full charge.

7. They need fresh, clean water occasionally. Sealed batteries have a
   built-in watering system, but flooded batteries do not. Be sure to
   check water levels, and fill with distilled water as needed (dirty
   water poisons them!)

8. They need to be kept at reasonable temperatures, that you would find
   comfortable. Not too hot, and not too cold. Lead-acid batteries are
   "cold-blooded", so the lower the temperature, the slower they get.
   Likewise, they can't "sweat", so high temperatures cook 'em to death.

9. Batteries can't talk. They won't whine when they're hungry, or cry
   when you hurt them. You have to check their state of health with
   instruments, like voltmeters ammeters and hydrometers.

10. There are different "breeds" of batteries, each with its own good
   and bad points. Slow plodding workhorse floodeds, but long lived.
   Racehorse AGMs that are fast and powerful, but short lived. Using
   the wrong breed of battery for the application, or unrealistic 
   expectations leads to disappointing results.

11. And some is just the "luck of the draw". For no obvious reason,
   identical batteries in the same vehicle will have some die young, and
   some seem to live forever.

The usual reason you see used EVs that say "needs batteries" is because
the previous owner treated the batteries cruelly. Whether by ignorance
or laziness, some or all of the above guidelines were violated. But
batteries are replaceable, and it usually means you can get the EV
"cheap".

But such problems can be cured. A little detective work to fix the
problems, and then some tender loving care will go a long way toward
getting the longest life possible on the next set of batteries.

Lee explains the tao of the fuse

A fuse is just a resistor. It contains a fat piece of metal at each end,
with a skinny piece of metal between them. It "blows" because the skinny
piece melts when the power dissipated in it heats it up to its melting
point. 

The voltage rating is defined by how long the skinny piece is. Low
voltage fuses have a very short skinny part, to keep the resistance down
and so the voltage drop low. But once it has blown, an arc can continue
across the big pieces.

Your fuse's 500v rating is probably for AC. AC arcs automatically stop
120 times a second as the AC line passes through zero, but a DC arc
won't stop until the gap is very large. Unless you have manufacturer's
data to the contrary, assume the DC rating is 1/4 of the AC voltage
rating.

Using a fuse at less than rated voltage has no effect on the current or
speed at which it blows. However, the higher the rated voltage, the
longer the skinny part, and so the higher the resistance of the fuse.

Since it's just a piece of metal, the actual current at which it blows
depends on the exact dimensions of the metal, and the ambient
temperature. There is quite a large variation. The specs will be
something like, "does not blow for 1 hour at rated current, and blows in
less than 1 minute at 200% of rated current."

As the current goes up, it blows faster. A fuse's I^2T is approximately
constant; so if you double the current, it blows 4 times faster.

Lee on surface mount and board prep

Surface mount is cheap, and small. But it is harder to build and less
reliable. You pays your money and takes your choice :-)

I have installed more surface mount parts by hand than I care to think
about. You really don't even need any adhesives at all. I usually work
under one of those big magnifying glasses with a circle fluorescent lamp
in it. The PC board is pre-tinned (pads are solder coated). I use
tweezers to position the part, and touch the iron to one pad. The solder
already on the board and part melt together to hold it in place. Then I
solder the rest of the pins.

On ICs, if everything is scrupulously clean, you can hold the board
vertically, and just slide the soldering iron tip down the row of pins,
walking a little ball of solder. The pins solder beautifully once you
get the knack.

The main problem with surface mount is that there is no component lead
length to absorb stress when the board flexes, or when parts expand and
contract with temperature. So vibration and temperature cycling causes
cracked solder joints.

The second problem is that repairs are likely to destroy the part and
the board. If it fails, you throw it away.

> I really wish someone made a cheap automatic drill press.

Same here. Machine tools are still expensive. Your best bet is to buy an
old one at 10 cents on the dollar.

People have made their own out of drill presses with stepper motors,
etc. 
Another method uses a pen plotter, with the pen replaced by a flex shaft
to a dremel moto-tool. This has the advantage that most PCB layout
software already knows how to drive plotters.

Another uses very thin PCB laminate, the kind used for multilayer
boards. They wrap the laminate around a drum, chuck it in a lathe, and
spin it. A duplicate drum has a printed photo of the desired copper
layout. A photocell and cutter move slowly along the drum as it spins.
The cutter removes the copper wherever the photocell sees light. When
you're done, the PCB laminate is glued to a thicker piece of board
material.