charger


Yesterday started out poorly. I only slept for 4 hours. After waking up at 4am, I headed over to my computer. There was a notification from Ebay about some US Electricar stuff that went up for auction. As it turns out, it was the same hardware that one of the guys in the USE group had mentioned was for sale. We thought it would be a private sale. But here it was on Ebay. I immediately posted that fact that it was on Ebay to the group. The boards were all suppose to be 65kw. But only 2 were 65kw, the other 6 were 50kw boards. So I looked at the name of the seller, and it looked vaguely familiar. I searched my email archives and found that I had corresponded with the guy in the past. So I wrote him a plea to not sell them on Ebay since some random buyer could end up with these important parts. He agreed to pull them from Ebay and sell them to me. Sometime later this week they should arrive. Also included were 2 charger boards and a dc-dc board. There was also 4th board that I have never seen before.

What I have done in the past with two other batches of boards I have received,
is to go through these boards carefully with my test fixture, and see if they
work or what they need to make them work. One 50kw board looks to have some
serious damage to the Mach220. I have replaced a couple Mach220’s already. But
that serious kind of damage may also have toasted some board traces. Worst case
the board becomes a parts donor. I hope the DSP chip is ok as it could be used
in another 50kw board. Almost every chip from the 50kw boards are missing. Since
the DSP chip cannot be copied, then the boards will always have to borrow a DSP
from another board.

The 65kw boards will go onto my test fixture to see if they can be lit up or
not. At least they have all of their chips. I’ll see if the 65kw chips are any
different than the 50kw chips. At least one of the 65kw boards has a red arrow
on it indicating that it needs something.

5 out of 6 of the 50kw boards are 2nd generation. They have a socket on the
Mach220 plus some other additions. I think the factory finally figured out that
when the Mach220 gets damaged, that unsoldering it from the board is dangerous.
At least with the sockets the Mach220’s can be swapped in and out for testing. I
have the code for the Mach 220’s so duplicating them is easy.

There is also a pair of charger boards and a dc-dc included. There is a 4th misc
board that I have never seen before. No idea what it does.

I know of 2 other sources that need boards. So if any of the 50kw boards are any
good, 2 of them will get shipped out asap. Usually when the chips are missing
the boards have issues.

All of the boards that run will have to be test driven to see if they exhibit
any of the classic dropout issues. As I was discussing the dropout issue last
night with a fellow member, he pointed out that every board we have could end up
with severe drop out issues just simply from driving them long enough. That is
exactly what has happened with a couple of the boards that I have. To me this
issue is 50% resolved. The last 50% will be tough.

So the next morning the pack was still soft. The voltage sagged right away. So I electrically removed about 14 cells from the pack so the charger could keep the current level up around 1-1.5 amps even at full voltage. This will overcharge the nicads and help equalize them. Flooded cells are the only ones you can get away with this. So the charger was programmed to stay on an extra 5 hours after full pack voltage, 400v, was reached. The pack was charged like this all week.

A couple of days ago, I noticed that the resting pack voltage after the charger shut off during the night, was very low. About 306 volts. This concerned me. The first day the resting pack voltage in the morning was 325v. But today it occurred to me that I may have finally gotten what I was trying to achieve. The pack’s cells are now all at the same state of charge. So the cell to cell voltage is closer. With 237 cells in circuit (14 removed), at 306 volts, that’s 1.29v each cell. That’s a bit low. Usually the cells are about 1.35v to 1.4v after sitting for hours. I am guessing that the cells hit the knee in the curve as a group, and the voltage starts to go down as the cells are overcharged. This is some fairly serious overcharging. But it shows that the cells now are more equalized.

Midweek I reduced the overcharge time from 5 hours to 2 hours.

This weekend I’ll reattach the 14 cells that were taken out of circuit and see how the whole pack is acting. Although the 14 cells did not get the huge overcharge, the pack should show improvement. I could add some overcharge to the 14 cells before closing the pack up just to try and bring them into the same state as the rest of the pack. I’ll actually make sure I do that.

The bottom line is that with 3 different versions of the same cell, they are getting worn out as exhibited by their impedance being high. This allows the pack voltage to rise artificially high and make the charger think the pack is full when in fact many of the cells are not fully charged, resulting in a sagging pack.

Isn’t debug fun? It sure separates the boys from the men, or me from my sanity Wink

I’ll be on vacation starting Monday. That excuse one for not having my BMS installed. #2 is that the second truck has taken all of my time to get corrections made to it’s various electrical systems. It’s basically done. Just needs a new pack. So the #1 truck is the tough vehicle to get a shielded cable from the pack to the interior of the truck. Once the cable is mounted through the wall of the pack, then adding the BMS is easy. Now I have Thundersky’s that I have been testing as well as 3 new 50ah Hi Power cells to test.

To look for noise it’s helpful to determine if it’s conducted or radiated noise. Steps that I use.

Conducted Emissions

1) I like to use clip on ferrite beads for initial debug. Easier and faster than adding components. The kind you see attached to a wall wart power supply or your pc monitor cable. 25-30mm long. 15-20mm in diameter. When picking them up from surplus locations, get a few different versions as you don’t know which RF material they are made from. Clip them onto both ends of the master bus cable. One at the master board and one at the first slave. Check for changes. Does the system work better? Verify with a scope, always.

2) Now repeat step one with the Slave bus, with all of the master bus ferrites removed. The slave bus could easily carry EMI/RFI and cause issues.

3) Repeat step one with ferrites on Master and Slave bus.

4) The shotgun approach is to just do both Master and Slave bus at the same time. But you won’t know the sources of noise as well.

If 1-4 improve function then it’s the noise is mostly conducted emissions. Although radiated emissions from the vehicle could turn into conducted emissions due to the huge amount of wiring we have to use.

5) Always twist pairs of cables to 4 turns per 25.4mm(1 inch) between slaves. Cordless drill works great for twisting wires together.

6) Use shielded cables with twisted pairs for Master to first slave cables.

Radiated Emissions

Here is a fantastic article on how to make a home made probe for sniffing EMI/RFI with your scope from a piece of coax a tiny ferrite bead, and some sandpaper. When I showed the crew at work this article, everyone had me making these probes for them.

http://electronicdesign.com/components/simple-homemade-sensors-solve-tough-emi-problems

Here is the probe I made from the article.

Above is the probe I made from the article.

Here is the probe I made from the article.

Above is the probe diagram from the article.

Below are scope shots using my probe on a project that has so much EMI that it smoked the processor and other drivers badly enough that my head with a full face helmet, hit the ground hard and made me unconscious. Had a concussion for a year. So EMI and I have become great friends!

There are EMI and RFI (aka E field) probes. An E field probe is just the ground of your scope probe tied to the probe tip. It shorts it in a dc sense. But for RFI, it’s a path to joy and harmony. If you make your probe ground lead a bit longer and coil it, the probe becomes much more sensitive to weak signals.

HBoth EMI and RFI probing examples of my concussion making machine (a home made self balancing scooter) are shown here.

Both EMI and RFI probing examples of my concussion making machine (a home made self balancing scooter) are shown here.

These scope shots showed me clearly at the time where the emissions were coming from. Each output from the processor got a 1k resistor to isolate it from the drivers. A 1k resistor was put on the output of the driver chips. These two steps did not reduce EMI, but did reduce it from getting into the sensitive parts. The next step was to reduce the EMI itself. I had used 250mm long ribbon cables for connecting the master board to two slaves (control board to 2 H-bridge boards). Normally the ribbon cables are about 50mm long. Reinstalling the 50mm cables did the trick. The EMI probe showed me the way. As you can see from the scope shots I also found EMI from the power supply inductor as well that I could follow with my handy EMI probe along a ground trace. That’s right. EMI was following the ground!!

So assume nothing, and measure everything!!

This truck just had a female connector hanging down low to plug into. But being that it was a female connector, try to imagine what the extension cord would look like. Hmmm. A male connector on each end....

This truck just had a female connector hanging down low to plug into. But being that it was a female connector, try to imagine what the extension cord would look like. Hmmm. A male connector on each end....

I hunted all over town for a piece of flat black plastic to make the ring adapter for attaching the outlet to the fuel door box. This oil drain pan was a good choice. I cut 4 ring adapters out of it just to have spares. I was able to easily CNC these parts out due to a an add on piece of software that I bought with my CNC software, Mach3. This add on made it so I could specify the triangle bolt pattern and the other features machined into the ring adapter with great ease.

I hunted all over town for a piece of flat black plastic to make the ring adapter for attaching the outlet to the fuel door box. This oil drain pan was a good choice. I cut 4 ring adapters out of it just to have spares. I was able to easily CNC these parts out due to a an add on piece of software that I bought with my CNC software, Mach3. This add on made it so I could specify the triangle bolt pattern and the other features machined into the ring adapter with great ease.

That large black plastic part is the fuel door box that was missing from the #2 truck. So I ordered it and many other parts from a local GM dealer. Also shown is the outlet and the CNC'd ring adapter.

That large black plastic part is the fuel door box that was missing from the #2 truck. So I ordered it and many other parts from a local GM dealer. Also shown is the outlet and the CNC'd ring adapter.

Here is the finished outlet install. All nice black parts. Even the screw heads are black. I was in a black out mood last night. The ring adapter is a bit too flexible, so it will get a second ring adapter to stiffen it up a bit.

Here is the finished outlet install. All nice black parts. Even the screw heads are black. I was in a black out mood last night. The ring adapter is a bit too flexible, so it will get a second ring adapter to stiffen it up a bit.

The buzzing is from the H-bridge that powers the IGBT’s. Half of the
fets are not getting a gate signal. The driver is not getting one of
it’s two gate signals. So I spent alot of time trying to buzz out the
board to find the pwm source for the H-bridge but could not. Anyone?

I’m glad I have a functional board now for reference. I can complete
my test fixture in minute detail. I’d like to duplicate the truck on
my bench so I can more completely test and characterize the board.
I’ve learned from rebuilding motor controls that just because
something spins a motor does not ensure that the various voltages and
pwm signals are at their nominal values. I’ve seen that a few times.
So I have a list of “test points” on my customers hardware that I go
thru and make sure are meeting spec. This took some time to figure
out. Our Dolphin boards need the same thing. I noticed that the pwm
firing the 300v supply chopper fet was 12v on one board and 10v on
another. Something is up. The board functions fine, but it strikes me
as trouble waiting to happen. A detailed test fixture makes looking at
these things much more thorough, accurate and repeatable, because
sometimes the tech gets tired 😉

Now where’s my celebration beer?

Here is the bridge board that helped save my Dolphin tonight!!

http://www.rotordesign.com/s10/fusepcbproto.jpg

My Dolphin Main board is now officially working!! I figured out how to
rework the bridge circuitry with minimum trauma to the Dolphin PCB.
Now the bridge is located on the new prototype fuse board as seen in
the above link.

Can there even be better news? So I turn on the ignition key and
everything boots up. Stable and fine. So I decide to try plugging into
120vac for some charging. Everything boots up again and then
pppppffffssstttttttkkkkkssstt!!……pppppffffssstttttttkkkkkssstt!!

What was that? So After the 3rd verification that something was wrong
I turned off all of the lights and fired her up in pitch darkness. Ya
know how polished the aluminum Dolphin case is on the inside? It was
acting like a mirror and reflecting back to me some high frequency,
low amperage intermittent arcing from under the charger!!

So I guess the charger needs to come out. I’m wondering if this was
the demon that trashed my main board! I’ll find out soon.

Feeling like I’ve conquered a small army of gremlins, I tried to fire
up another board that had the same sort of damage. The board is
buzzing back at me when power is applied on the bench. All 4 of the
regulators and the chopper fet are working fine. The pwm to the
chopper fet is clean and pretty. Not sure where the buzzing is coming
from but it’s keeping the board from talking to the laptop.

I’m not much of a drinker and it’s time for a beer!

1 down, 3 to go.

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