for working on the truck
This note began with a list of Do's and Dont's from Michael
Mutch on the preparations needed to work on the EV. I've
removed some personal notes from the original email and
added my own emphasis where I thought it helpful.
Simply put, the electric power in the truck's battery pack
can kill you
if it should find a path between your hands as that path
travels near your heart. If the electricity finds a shorter
path, say across fingers of the same hand, it can severely
burn you. The power in the batteries is way more than is
needed to weld steel.
The metal of the truck is indirectly connected to the
Negative side of the battery pack. If you lean on the side of the
truck and touch a wrench to the Positive side of the battery pack,
the electricity will try to run through your body, between your
arms and across your chest. It isn't always fatal but why chance it?
Even when it doesn't kill, the high currents caused by a short
circuit can cause the batteries to generate a dangerous amount of
Also, keep in mind that you don't want to cause a short circuit
even if your body is safe. It's very easy to put a wrench on a
nut and accidently let the body of the wrench touch other metal,
like the frame which holds the batteries. The resultant lightning
bolt can so surprise you that your hand will move at very high
velocity out of the area. I have gotten severe cuts (on other
projects) when something like this has happened.
Thus, there are some important rules to follow when setting
up to work on the truck. Ignore them at your peril.
Most of the safety warnings I encounter are exaggerated thus
I sometimes ignore such warnings. However, I consider the EV
environment dangerous enough to have helped construct this
General Areas to Consider
- Work environment
- Other people
- Electric Vehicle Prep
- allow some time to learn. don't rush it.
- study the wiring
- you should know function, quirks, risks:
- batteries, and how pack is wired. rules of engagement.
- 12v system. DC-DC.
- brake assist
- devices inside the cab.
- fuse locations.
- ask questions of more knowledgeable people.
- provide easy access to ABC type fire extinguisher.
- consider lighting, workspace, tool access, manuals, drawings.
- tape or dip the ends of wrenches.
The 'dip' coating for tools is called "liquid electrical tape". It's
made by Tool Dip and is available from Harbor Freight.
- electrical device access: voltmeter, ...
- consider putting insulating pads (eg: rubber bath mats) around EV work zones.
- consider the possible dangers to others if you have to leave
when the work is partially done.
- Your bod: be rested, undistracted, feeling good.
- Your Plan:
- plan your approach. consider safety aspects.
- plan enough time, including a surprise or two. don't rush.
- when plans change, take a break, re-consider safety implications.
- don't wear loose metal neck chains, watches, buckles.
- DO wear insulating gloves.
- DO wear rubber soled shoes.
- choose attendant(s) wisely. The best is to have just 1 person present,
in case you get into trouble.
- remind others that a potentially lethal condition exists
- remind others that you'll need to stay focused.
- tell others what to expect. Describe your plan.
- define the bounds of a "don't touch" policy.
Electric Vehicle Prep
Initial check list:
- Parking brake set
- Transmission in neutral
- Ignition key Off
- ? Master Controller On/Off Switch ?
- Cell phone (distractions) Off (?)
The bulk of this section describes how to disconnect the battery
pack such that you can work on the controller etc. The sequence
described here is just run in reverse to restore the EV to its
The main traction pack voltage is isolated from the chassis, BUT
there is ground available through the dc-dc converter. If you
short the pack to chassis ground there will be sparks!
I will refer to the truck from the front looking back.
Disconnect the long cable that lies across the rear battery
bank and connects to the rear right battery (in the rear pack).
This will create two banks. One of 5 batteries (front) and one
of 15 (rear).
- Disconnect the cable that connects the shunt in the grey
plastic junction box in front to the pos on the front left
battery in the rear pack.
Disconnect the cable from controller neg to battery neg.
Front pack - left rear battery.
The traction pack is now isolated from the controller and
the dc-dc converter;
however, there is
still 120 volts in the capacitors
inside the controller box!
Use a jumper from controller B+ to a good ground (metal fence?
hose bib?) to discharge the caps. (you may have to scrape off a
little of the protective coating on the controller terminals to
accomplish this) Repeat this with the M terminal to make sure.
Check the terminals for voltage before proceeding! The shock from
the undischarged caps is definitely jarring!
It is now safe to work!
When you reconnect the battery pack, do so in the opposite order.
Negative first, positive last. I like to connect the long cable
across the rear pack last. Expect a small spark, it is normal