4Springs' Brumby

Post up a thread for your EV. Progress pics, description and assorted alliteration
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Post by Thalass » Fri, 19 Feb 2016, 18:41

Man, that is one fine working mans EV you have there.
I'll drive an electric vehicle one day.

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Post by 4Springs » Sun, 06 Mar 2016, 14:17

Ok, it is time to document my second charger...

When I first built the car it had a lead-acid battery, and so I had a lead-acid charger. When I upgraded to a lithium battery I bought a lithium charger. The old charger didn't sell so it sat in the shed. Once I had made my BMS and gained some experience in these matters I realised that my lead-acid charger could also be used to charge the lithium pack.
After some discussion with Paul9 and others over here, I did the following:
1. Moved the lithium charger (TC Charger) from under the bonnet to under the tray behind the back wheels.
2. Installed the lead-acid charger next to the lithium one.

Image

This photo is from the rear of the vehicle. You can see the galvanised iron brackets (held on in part by two dodgy-looking tek screws!). These hold a plywood sheet (the brown bit) up against the bottom of the tray. The plywood forms a "base" for me to screw into so that I didn't have to pierce the tray in multiple places.
The lithium charger is black and is on the left. The lead-acid charger is yellow.
When I look at this photo I cringe a bit when I see the tow bar bolts above where the camera is. I have hit my head and other body parts on this towbar many times and now have an instinctive fear of it - apparently even from photos!

Image

This photo is from the right-hand side of the vehicle.
The grey box contains some connections and some electronics, explained later.

Image

Image

Image

These photos show how you use the two chargers. The first charger uses a retractable cord that comes from behind the fuel filler door on the outside of the vehicle. We normally just use this cord. Plug it into any 10A 240V socket and it will draw about 10A.
The second charger is powered via the black socket inside the tray. One photo shows it with its grey foam cover, and another shows it with a yellow extension cord plugged in. So if you want to charge faster, and have a second 10A 240V socket available, you can plug an extension cord in here to power the second charger. The second charger will only work when the first charger is plugged in, and draws about 5A.

Now if you are following along so far, and haven't peeked at the next photo, you may have realised that with both chargers connected I will draw about 15A. And you might wonder if I wouldn't have been better to wire into a single 15A plug? Well here is my cunning plan:
Image

This photo shows the 15A "powerboard" that I bought from Bunnings. It has a 15A plug (note the wide earth pin) and four 15A sockets. So I can plug this into a 15A socket and plug my two chargers into it as shown. There is a 15A circuit breaker in the device, so it will trip if someone comes along and plugs something else in at the same time.

The electronics I spoke about earlier is to do with turning the second charger off. I have a relay which is controlled by the BMS. When the battery is down and needs charging the BMS switches the relay on to provide 240VAC to the second charger. Once the battery voltage indicates that the battery is nearly full the BMS switches the second charger off, and puts the main charger into dribble mode.
I didn't have any outputs left over on the BMS, so I had to run this relay off the "enable" line provided for the TC Charger. Got it to work after some fiddling...

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Post by 4Springs » Sun, 06 Mar 2016, 14:33

I have left a space under there for a second TC Charger the same size as the first one. Currently I am using 10A + 5A = 15A * 240V = 3.5kW or so. This charges at about 15km (of range) per hour. If I installed a second 10A charger, and therefore had three chargers altogether, then I could charge at about 25km per hour. So in that case I could charge from 3 x 10A sockets, or 1 x 10A and 1 x 15A, or make up a converter to charge from a J1772.

I did have a problem with the second charger. Occasionally it would stop charging and flash an error light. The user manual was not very helpful, it said to reset it, or if it persists to contact the manufacturer. This only happened after a few hours of charging, and would be fine with a reset as suggested. I wondered whether it might be overheating (despite there being a different error light for overheating), and installed a fan. But the error still occurred.
So I settled on a software fix. I reprogrammed the BMS to have a short rest from charging every 2 hours. 240VAC power is now removed from the second charger every two hours, hopefully resetting any errors that may have occurred.

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Post by coulomb » Sun, 06 Mar 2016, 16:41

4Springs wrote: 240VAC power is now removed from the second charger every two hours, hopefully resetting any errors that may have occurred.

I'm a bit nervous about interrupting power to Elcon/TC chargers when drawing significant power. They draw a fearsome arc, and I have suspicions that the bridge rectifier may get blown up more often when doing this.

It would be great if the BMS could disconnect the enable line, so the charger draws very low power, then turn off the AC supply. Enable and mains can come on together for simplicity. Of course, this is more complexity, but it sounds like your BMS is very programmable.
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Post by 4Springs » Sun, 06 Mar 2016, 19:20

coulomb wrote:I'm a bit nervous about interrupting power to Elcon/TC chargers when drawing significant power. They draw a fearsome arc, and I have suspicions that the bridge rectifier may get blown up more often when doing this.

It would be great if the BMS could disconnect the enable line, so the charger draws very low power, then turn off the AC supply. Enable and mains can come on together for simplicity. Of course, this is more complexity, but it sounds like your BMS is very programmable.

Thanks coulomb,
The main charger (the 10A TC) is controlled by the BMS and throttles back nicely. This second charger is the one that is unceremoniously cut off, and this is nominally a Chennic. I describe it a bit in this thread here.
I agree that a less drastic way to switch it off would be ideal, but there doesn't seem to be any. It would turn itself down/off if the voltage climbed high enough, but that won't happen with this lithium pack. There are no control lines at all unfortunately.
I was thinking that this was the way that I used to control this charger when connected to my lead-acid pack, but reading back through that thread it looks like I turned it off with a relay only when it had reduced its output current. With the current set-up it will be cut off in full (5A) flight.

Before I came up with the software solution I had toyed with the idea of a circuit that would cycle the power whenever the Chennic's error LED came on. This would be a nicer solution, but quite a bit more work...



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Post by 4Springs » Mon, 06 Jun 2016, 00:17

Latest project:
Image
This box takes 240 VAC in from the left, and delivers it (or does not) to the socket at the top. The circuit board is a Jaycar remote control receiver. So the idea is that when I press button 1 on the remote control the box turns on the 240 V, and when I press button 2 it turns off. The remote control is sitting next to the box.

Image
This is it installed behind the seats. The rocker switch can turn off the 240 V - it is shown in the on position. The red momentary switch turns on the 240 V to the socket, the same as pressing button 1 on the remote.

Image
And here is a picture showing the true purpose of the installation - a heater! For some reason the picture is sideways, but anyway I can turn on this little heater from the house when I get up in the morning, and hopefully the car will be warm by the time I get out there.
I've made the heater easy to remove for the warmer months. For car shows I can plug something else into the socket. A strobe light perhaps? Or a loudspeaker that yells at people? A smoke machine!

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Post by Paul9 » Mon, 06 Jun 2016, 19:03

Good idea 4Springs!

Tasmania is not a tropical state is it? No banana trees and sugar cane?

Cheers
Paul

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Post by Paul9 » Tue, 07 Jun 2016, 03:45

Hi 4Springs

At car shows could you plug your charger into the socket and recharge your batteries if the car show didn't have any spare sockets? Maybe save you some money?

Just me trying to think of other ideas apart from loudspeakers and strobe lights.

Cheers
Paul

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Post by 4Springs » Wed, 08 Jun 2016, 00:25

Paul9 wrote: At car shows could you plug your charger into the socket and recharge your batteries if the car show didn't have any spare sockets? Maybe save you some money?
HAHAHAHAHAHAHA
I'll put you with the people who say I should put a wind turbine on it. Or an alternator.

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Post by Paul9 » Wed, 08 Jun 2016, 01:36

Well I originally thought (after a few red wines) that maybe you could plug in a charger and then plug in a dc-dc converter to the charger to get your 12v then plug in an inverter to get back up to 240v ac and then plug another charger into the inverter!

The above, combined with the wind turbine you suggested, could keep your car going almost ad infinitum!

I have not had my original idea above patented or anything yet, so if you want to adopt that arrangement, that would be fine. I am a huge supporter of open source anything.

Cheers
Paul

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Post by carnut1100 » Mon, 22 Aug 2016, 05:16

I was lucky enough o have a short drive in this machine a few days ago.
It was the first DC car I've driven. Also the first with a transmission.
It's an awesome little rig!
You've done a top job mate, full marks!

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Re: 4Springs' Brumby

Post by 4Springs » Mon, 12 Aug 2019, 18:23

The Brumby is still going well, but I'm thinking it might be time for a battery upgrade. The target range for this lithium (LFP)pack was 80km. My very first test took me just over 100km, in summer, fairly slow stop/start driving. That made the 80km target achievable under most conditions.
The battery has aged a bit now, it is about 4 years and perhaps 50,000 km. My guess is that the same conditions as the first test would get me about 80km (i.e. 80% of its original capacity). The other day we got 60km before the BMS warning light came on - highway driving on a cold winter day. The ambient temperature that day was about zero, and the battery was probably below 10 degrees.

Francisco is offering these LG cells: viewtopic.php?f=17&t=5909

My current pack is:
48 LFP cells (3.2V nominal)
211 kg
20 kWh

With the LG cells I think I can fit:
200 NCM cells (3.6V nominal). 40 in series, 5 in parallel.
194 kg
45 kWh

With this pack I might expect 225 km range when new, and 180 km when the battery is degraded to 80%. Once the battery is aged a bit, we might get 135 km on the highway on a cold day. Certainly a step up! This would allow round-trips to Devonport, which is 70 km away.

I have one large rear battery box, and two front boxes to help distribute some of the weight to the front. The size and shape of these cells means that I think I can fit 150 in the back box without modification. It will be fairly tight in two dimensions, but there is plenty of height. This is what the rear box looks like, the rear of the rear box is a lid:
IMG_3799.JPG
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I've done some drawings to see how things will fit.
Rear_Box_Top_View.png
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Rear_Box_Rear_View_6.png
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These cells in the rear box are shown in groups of 5, although in reality they will all be squished together in one big block of 25 cells. There are 6 blocks of 25 in the rear box.
There is not much room! I hope that the 11.5 mm nominal thickness is accurate. If so, there is about 22 mm of spare space between the front and rear of the rear box.
There is also not much space left to right. Here is another way to arrange the cells to make more room:
Rear_Box_Side_View_4.png
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This arrangement overlaps the tabs on the right-hand two blocks of cells, making one big block of 50 cells. There are two disadvantages to this, the first is that it will be heavy (approaching 50 kg), and the second is that it will be awkward. I'd really like to be able to get at any cell with the minimum of fuss. If I have to access one of the connections I'm going to have to pull the block of cells out. Three blocks of 25 kg will make this much easier than one of 25 kg and one of 50 kg.

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Re: 4Springs' Brumby

Post by 4Springs » Mon, 12 Aug 2019, 18:41

The front two boxes are identical, and they will need to be re-made. They will be a bit longer in length and a bit shorter in height. Making new boxes means that the swap-over can be relatively quick, so the car will be off the road for a minimum of time.
Front_Box.png
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These front boxes will be relatively easy to fill. The box will be made the right size for the cells, and they'll just sit in there without needing any strapping etc.. A shelf on top of the first layer will make a place for the second layer to sit. I'm not sure exactly what I'll do with the rear cells, possibly put a plate each end of the 25 and strap them to a board. Slide the board into place.

The observant among you may have noticed that I have drawn 150 cells in the rear box, plus 30 in each of the two front boxes, which adds up to 210 cells, and that I previously stated that I'm looking at 200 cells. So 10 of them are not required. I'll have a gap somewhere - most likely in the rear box I think, since the front ones are so neat.

I have planned on having zero cooling with this battery pack. The cell specifications are 10-45 degrees continuous, with excursions to -30 and +55 degrees. I've never seen it higher than about 35 degrees in the current (LFP) battery box. So at this stage I'm working on the theory that the NCM cells will generate no more heat than the LFP cells, and thus won't need to be cooled in this application. I will, however, put in battery warmers for the cold weather. I have these now, they run off 240VAC, so they are on when plugged into the wall.

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Re: 4Springs' Brumby

Post by 4Springs » Mon, 12 Aug 2019, 19:16

How am I going to connect these cells together?
Francisco has posted a picture of how he has done it:
Francisco_Al.png
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His cells are three in parallel. What you can see here is three cells connected to the left side of an aluminium block, then the next three cells connected to the right side of the block. In the photo is four groups of three parallel cells, in turn connected in series to make about 14V.
The clamp that looks like a flat plate is actually a spring. It starts out curved, but you do up the bolts to flatten it to clamp the cell tabs together.

I'm looking at 5 in parallel, which makes this a bit more tricky. Francisco reckons that I should get 4, but won't get 5 clamped in one spot. My equivalent to the above is that I need 10 cells connected together (two groups of 5, like Francisco's two groups of 3). If I did it with Francisco's aluminium blocks then I'd need spacers to make them fit.

I've come up with another idea:
Cell_Connections.png
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If Francisco's photo is from the end, my drawing is from the top. You can see the top bolt, but it obscures the bottom bolt.
Instead of solid aluminium (with threaded holes), I've drawn aluminium channel. This is available in various sizes, including the one I've drawn which is 32 x 25 mm (outside dimensions), 3mm thick.

Advantages of doing it this way is that it should be lighter, and probably easier to assemble. Uses more bolts though.
I'm not sure that the channel would stand up to the spring pressure.
I'm not sure about that central spring placement. I might need two springs, or perhaps put all the tabs on one side of the spring? Would I get away without a spring there? I'd have to test it.
The current is flowing from the left 5 cells into the right 5 cells. The way I've drawn it, the central spring conducts all of the current. I was assuming that this spring was steel, but looking at the photos it might be aluminium? If so I think it should be ok. But better if it wasn't there, as the aluminium channel has plenty of surface area.

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Re: 4Springs' Brumby

Post by francisco.shi » Tue, 13 Aug 2019, 03:43

You do not need the middle spring.
You can just put aluminium spacers in the middle and two long bolts that hold the whole lot. The spacers would be thick enough that you do not need the spring in the middle. You only need the two end springs. The spring is steel and will not conduct very well.
The bus bar in this case would be more like spacers and would have a hole all the way thru and are only 12mm x 65mm in cross section.
I will try to make a sketch and send it a bit later.

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Re: 4Springs' Brumby

Post by francisco.shi » Tue, 13 Aug 2019, 06:41

This is how I would do it.
1565649376595133065444.jpg
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The blocks in the middle should be strong enough they will stay flat. You could do away with the end springs if you put a thick enough bit of aluminium but I think the spring is easier and uses less space.

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Re: 4Springs' Brumby

Post by francisco.shi » Tue, 13 Aug 2019, 06:45

For the back box could you rotate the cells so they are flat on the 310mm? That would fit the 137mm perfectly. Then either put more cells in the back box and less at the front or make the back box smaller. I would also keep the cells all together. The gap in the middle will make it really messy to get the wires in and out. If you leave the gap on the end you can put the output wires on one side with the bolts for the terminals easy to access.

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Re: 4Springs' Brumby

Post by francisco.shi » Tue, 13 Aug 2019, 07:29

I think you could get 6 blocks of 30 instead of 6 blocks of 25.
As for being able to get to any contact with no fuss it is a little difficult. One of the good things about having the tabs on opposite sides of the cells is that you use very little space for the interconnects and they can be put inside the battery. It makes the finished pack very compact and neat but it is not easy to get to the inside cells. The moment you try to make it easy to get to the inside cells you add lots of complexity and wasted space.
The cells ar very close to 11.5.
I have a 0.4mm plate between them for cooling then I compress them until they end up with a 12mm pitch. The force I use for clamping is just enough to make the cells the specified thickness. If I compress them more they will get thinner but not by much. So I just clamp them until they get to 11.6mm so I would say you are ok to assume they are 11.5.

Also after thinking about your pack a little more I think your idea of the Aluminium channels will probably be better because you will have trouble getting the threaded rod on the end not to touch the next set of cells while you are assembling it.
You should put a spring on either side of the bolts. So 6 all together. If the channel wall thickness is thick enough you probably only need one spring on each end (like in your drawing but without the middle spring) I just don't know how thick the channel will need to be And you will still have to put some spring washers to stop the bolts getting loose.
Do not put the spring in the middle as in your drawing because the spring will only push evenly on one side. The other side of the spring will only have pressure on the ends.

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Re: 4Springs' Brumby

Post by 4Springs » Tue, 13 Aug 2019, 18:38

francisco.shi wrote:
Tue, 13 Aug 2019, 06:45
For the back box could you rotate the cells so they are flat on the 310mm? That would fit the 137mm perfectly. Then either put more cells in the back box and less at the front or make the back box smaller. I would also keep the cells all together. The gap in the middle will make it really messy to get the wires in and out. If you leave the gap on the end you can put the output wires on one side with the bolts for the terminals easy to access.
I thought about putting cells on their flat to start with. In the back box I could fit about 25 high. This would mean though that the bottom cell would have 25 kg sitting on top of it - and in a car it will be jiggling all the time as well. Even if this was not bad for the cells, it would still mean inconsistencies between cells. Each cell in the pile (ahem) would have a different amount of compression, which might lead to differences in capacity, which might lead to difficulties in balancing, and perhaps premature ageing of some cells. I don't know if any of this is practically true, but it sounds like something to avoid if possible. Also, there are heaters underneath the cells, so the bottom cell would be much warmer than the top one.
My current idea is to put the upper level of cells on a shelf, rather than sit them on the lower cells. This way there is no weight on the bottom cells, and I can pull a bottom group of cells out if required.
I have a bit of room to work with height-wise in the rear box. So I think I'd connect each block of cells with flexible cables, and have those cables sitting on top of the cell blocks. This would let me attach the cables, then push the blocks into place. But all of that is probably best worked out once I get the cells...

Although it would be great to remove the battery boxes from the front, I need to leave some cells there for better weight distribution. This was a requirement by the engineer of the original build. The front boxes can be replaced, but the rear box would be difficult to modify (e.g. make it smaller), as the tray liner is sprayed over it to make a water-tight seal. It could perhaps be made a bit shorter
francisco.shi wrote:
Tue, 13 Aug 2019, 06:45
Also after thinking about your pack a little more I think your idea of the Aluminium channels will probably be better because you will have trouble getting the threaded rod on the end not to touch the next set of cells while you are assembling it.
Good point - I hadn't thought of that.
I was also thinking about a long threaded rod, either with solid aluminium or with the channels. But it would mean everything would need to be lined up ready when the bolt was tightened. With smaller, more numerous bolts I'll be able to assemble a few cells at a time.

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Re: 4Springs' Brumby

Post by brunohill » Tue, 13 Aug 2019, 21:07

Do you put a few batteries where the fuel tank was? I believe it is under the tray where your current rear batteries are and quite well protected.

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Re: 4Springs' Brumby

Post by francisco.shi » Wed, 14 Aug 2019, 05:53

From what I have read up you need around 10psi minimum pressure to keep the cells from expanding during operation. That is about 270kg per pouch. I do not think 25kg extra will make much difference.

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