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Post by 4Springs » Sat, 19 Jan 2013, 22:06

The time has come to start thinking about lithium batteries for my ute. First step is to plan the required battery pack. Once I have that decided, I can start building the BMS (I’m keen on using Neville’s open source one). Here is my preliminary figuring, I thought I'd post it here so people can point out my errors!

Factors to consider when deciding what batteries to buy:
1.     Space – they need to fit in the existing battery boxes.
2.     Weight – they need to be no more than the existing pack (500kg), but there is advantage to every kilo saved.
3.     Required Range.
4.     Voltage – my Kelly controller can handle up to 180V. I am assuming that I will need a new charger.

Range:
The current vehicle will not do a return trip to Launceston on a single charge. Driving there uses about half (on the Zeva modified fuel gauge), and driving back uses a full charge. It would be great if I could increase the range to do the whole trip on one charge.
Based on my usage logs, I can see that when the fuel gauge is on half, it takes about 7kWh to recharge. When the gauge is on empty, it takes about 13kWh to charge. So the target for my new battery size is 7 + 13 = 20kWh.
I am being conservative by basing my calculations on data with all the inefficiencies built in. So I realise that the batteries don’t supply 20kWh for that round trip, they supply less than that, but it takes 20kWh for me to charge them up. A lighter battery will also help with using less power.

A quick trip to the EV Power website reveals that there is a LiFePO4 130Ah 3.2V cell. 48 of these adds up to 154V, 20kWh and 211kg. The size means that they should fit into three of my five existing battery boxes snugly.

Benefits:
•     I can remove the two most difficult of my battery boxes. The size of one of the under-bonnet ones could also be reduced, leaving more room under there (aircon perhaps?).
•     Weight distribution is roughly the same.
•     Total battery weight is reduced by 300kg (although there may be weight gains in the connectors and charger).

With lead-acid, the Ah rating is normally given as a C20 rate. So my 140Ah lead-acid batteries do not give me 140Ah if I discharge them over 60 minutes. They give me approx 85Ah. The LiFePO4 cells are listed as 130Ah. I am assuming that they will give me 130Ah in my application. The Brumby will normally draw about 100-200A, but will draw a bit over 500A under heavy load.

How does the temperature affect these batteries? My current set-up has heaters to keep the batteries warm. It doesn’t seem that this is a problem for lithiums? Batteries would get down to zero degrees on cold mornings. Summertime temperatures are up to about 30° max. Would the cells heat up appreciably under the estimated load?

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Post by jonescg » Sat, 19 Jan 2013, 22:45

Sounds like you could go all out in a decent pack and no matter what you do you will come out in front. The CALBs have been pretty solid to date, just keep them balanced and all will be well. Most lithium dislikes cold weather, but LiFePO4 is one of the better performers in sub zero weather.

I've been budgeting 37 kWh for my CRX, and this will weigh about 230 kg including all the copper. So even 250 kg of garden variety LiFePO4 will get you a long way.
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Post by coulomb » Sat, 19 Jan 2013, 23:35

jonescg wrote: I've been budgeting 37 kWh for my CRX, and this will weigh about 230 kg including all the copper.

Wow. With our 40 Ah CALB cells, 37 kWh would weigh 445 kg, and that's just cells, not including copper, the box to hold them, BMS, cables, etc. Granted, the larger cells have better energy to weight ratios, but it's not a huge difference.
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Post by jonescg » Sun, 20 Jan 2013, 00:16

Without derailing this thread too much... the 230 kg didn't include a box to house them, nore al of the switchgear to isolate them, so let's call it an honest 250 kg. All this depends on the funds, of course. Li(NiMnCoO2) has impressive specific energy (175 Wh/kg) but it's volumetric density (340 Wh/l) is what makes it so attractive. It won't absorb all of your boot space.

So 4Springs, with all the weight and space available, you could go for some EIG cells and have an epic pack. It won't be cheap though Image
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Post by Canberra32 » Sun, 20 Jan 2013, 22:41

I have a new pack of 180ah batteries with bms and charger for sale at the moment :) it's a 27kwh pack if your interested :)

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Post by Canberra32 » Sun, 20 Jan 2013, 22:44

I should prob add its 268kg :)
Pm me if you want mor info :) I'm getting rid of them cheaper than they sell for as am about to move workshops so need to reinvent myself again in about 6months :)

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Post by 4Springs » Mon, 21 Jan 2013, 01:56

Canberra32 wrote: I have a new pack of 180ah batteries with bms and charger for sale at the moment :) it's a 27kwh pack if your interested :)

I did notice your pack for sale, but I'm not ready to buy quite yet. My hope is that my current pack will let me know when it is getting towards its end of life, and that is when I'll buy the next one. Hopefully a year or two away yet! I'm planning now so that I can start the long process of building my BMS.
27kWh would be nice though, I could drive a long long way...

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Post by Canberra32 » Mon, 21 Jan 2013, 02:18

Well it's going cheaper than normal so was just putting it out there :)
If it doesn't sell in next two or three months ill prob keep it trying to lessen the stuff I have to move to the new workshop because all my stuff will have to go in a container while building so less is more :) someone will get a bargain maybe :)

Also if you do plan for future remember the 180cells have the lightest weight for the power storage basically the reason I bought it :) and like you 48cells :) just I can draw over 1000 amps with my controller :)


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Post by 4Springs » Mon, 21 Jan 2013, 02:29

jonescg wrote:
So 4Springs, with all the weight and space available, you could go for some EIG cells and have an epic pack. It won't be cheap though Image

I hadn't heard of EIG, so I went and looked them up. I can see what you mean about an epic pack! If I used 500kg of these suckers then it would be 87kWh, giving me a range of 335km! At what cost I don't know, I didn't see any actual prices. They do look fiddly, don't they? Funny pouch things that have to be compressed, with annoying tabs to connect to. And 600 cells would be an awful lot of work to hook up!

In reality I'd like to reduce the weight, it is not the best handling machine as it is. I think that 20kWh should be enough.
I remember someone saying somewhere that the change from lead-acid to lithium was as big a step as from ICE to electric. Well I can see that it will be a similar price at least! The 130Ah pack I'm looking at costs $8500 + connectors + BMS + charger + freight. My entire conversion so far has cost $12000.

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Post by Canberra32 » Mon, 21 Jan 2013, 11:09

But is that 12000 including the old batteries? Coz you can minus that cost because hey should have payed for them selves by the time you change em :)
I got my pack from ev-power :) Rod was very good for service :) even after I ordered the pack I needed to change the pack size so he re absorbed mine and ordered my new pack :)
Very few places would do that :)

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Post by 4Springs » Tue, 22 Jan 2013, 01:57

Canberra32 wrote: But is that 12000 including the old batteries? Coz you can minus that cost because hey should have payed for them selves by the time you change em :)

Yes, 12000 includes 4000 for batteries and 400 odd for charger. I might even be able to get a few $ back if I can sell the old batteries again. My understanding is that tired lead-acids should still be fine for a few years for an application that doesn't need power quick. So someone might want some for a shack or boat.

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Post by Canberra32 » Tue, 22 Jan 2013, 02:03

Or sell the led :)

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Post by 4Springs » Sat, 23 Nov 2013, 13:59

Has anyone any comments on the use of plastic packing straps to compress/restrict lithium cells?

I have one large box which will not restrict the cells itself, I'll need to provide some sort of restriction for them inside the box. I had thought of the packing straps, since they are light, cheap, non-conductive and not bulky. Then I saw that Arber has used them. This is his website, it is not in English, but as he says "pictures tell all". The battery packs are about 1/3 of the way down the page:Arber's Website. He has used three straps per pack, with two or three cells in each pack.
My original idea was to use a plate at each side. This would be steel, aluminium, plywood or perhaps cut-down plastic chopping boards. The straps would go around them, so the cells were sandwiched between the plates. I notice that Arber hasn't done this though (by the look of it), he has just used the straps. This would be easier/lighter/smaller.

I can borrow a tool to apply the packing straps, I just need to buy the straps and clips.

So is it a good idea?

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Post by Canberra32 » Sat, 23 Nov 2013, 14:44

Yes but definitely use the plates at each end or driving vibration may result in the straps cutting into the case of the cells

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Post by 4Springs » Sat, 07 Dec 2013, 02:14

Ok, I've bought myself a strapper through ebay. Around $100 for a kit including some strapping and clips - it seems to do the job...

I'm wondering do I need to do anything special when I connect the cells up in the vehicle?
I have LFP cells, which seem to have one copper terminal and one silver-coloured one (aluminium?). The cell interconnects that I purchased from EV Power are also silver-coloured and non-magnetic. (they don't look like aluminium, they are shiny like bright steel). I will be connecting to copper cable, with some lugs tinned and some bare copper.
If these terminals are aluminium, should I be cleaning them in some way immediately before making the connections? I understand that aluminium oxide might be a problem when it comes to electrical conduction.

I seem to remember someone once saying that there was a particular product to use on electrical connections in EVs? Not sure if this was a cleaning product or a protective coating.

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Post by coulomb » Sat, 07 Dec 2013, 03:01

4Springs wrote: I have LFP cells, which seem to have one copper terminal and one silver-coloured one (aluminium?).
Yes, it's aluminium.
The cell interconnects that I purchased from EV Power are also silver-coloured and non-magnetic.
They will be coated copper; the coating might be tin, nickel, or similar.
If these terminals are aluminium, should I be cleaning them in some way immediately before making the connections? I understand that aluminium oxide might be a problem when it comes to electrical conduction.
Exactly, so you should give them a light sanding to make them bright and shiny (the copper and the aluminium terminals both), then apply a thin smear of grease that will keep out moisture and air. The word Noalox comes to mind, but there are others, and EVworks at least used to stock it. I think the stuff from EV Works is called Cabac. Weber and I use Cabac (if I've remembered correctly) on the MX-5.

Image

Discussed here: LiFePO4 terminals and straps chemistry.
Not sure if this was a cleaning product or a protective coating.

It actually just keeps the air and water away from the terminals; it should not actually end up between the actively conducting surfaces. You should also use this stuff inside cable lugs before crimping them to copper cable.
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Post by 4Springs » Sat, 07 Dec 2013, 13:52

Thanks coulomb, I thought the information might be out there somewhere, but hadn't had any luck finding it.
I'll have a look for Cabac EJC300 at my local electrical wholesalers.

I've been thinking about the order of the terminal hardware.

I was provided with bolts, split washers and flat washers. The bolts are non-magnetic, while the washers are slightly magnetic. I'm assuming they are stainless steel. I also have my BMS modules to include. This is the order that I've come up with:

ImageImageImage
So at the bottom I have an interconnecting lug (directly against the terminal of the cell). Then a flat washer to make sure that pressure is applied evenly to the circuit board (because the lugs are not perfectly flat). Then the circuit board, then another flat washer, then the split washer.
I'm not sure about that second (top) flat washer. I like the idea of not having it, since the split washer would work very well digging into the circuit board. But I'm afraid that I'll wreck the circuit board if I have to disconnect the bolt at some stage. So that extra flat washer is to provide some protection to the board, even if it nullifies the effect of the split washer to some extent.

Before assembly I'll wash all components, possibly in circuit board cleaning solution. Then I'll apply grease as per coulomb's suggestion to all components. I'll wear gloves when handling the cleaned components to avoid fingerprints.

Does this sound right? Any further suggestions?

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Post by acmotor » Sat, 07 Dec 2013, 18:03

Some thoughts,

Do not put the zinc powdered jointing paste on the thread of the bolt. The zinc powder is in a deliberately sharp angular form that, while soft, behaves much like sand in a thread. The risk is of damaging the thread. The paste is an electrical jointing compound, not a thread lubricant. Note. the hold down force of a bolt is increased (before thread strip/pullout) by using a grease on the thread and particularly in the case of an aluminium thread that is prone to 'picking up' and failing before ultimate downforce. Rubb some of the jointing compound between your fingers and you will feel the grit.

The 'grease' in the jointing compound is petroleum based. You can use a tiny ! smear of a pure petroleum jelly like Vaseline on the bolt thread to control corrosion and provide lubrication for tightening. Tiny is often done well by 'put some on then wipe it off again'.

The current path will not be through the bolt, washers, PCB PTH these have relatively low conductance compared to the copper strap/lug so don't go overboard with jointing compound in that bolt path. The real current will flow to the strap/cable lug. Clean all those mating faces. Emery paper the terminals to clean metal immediately prior to use or a smear coat of the jointing compound will preserve the surface for a while, but keep dust off.... and same for strap if it is tarnished. Is that a solid or layered strap ? Layered straps can get oxidised between layers... not good. Keep the air off them until ready to use. Even a wipe with CRC if they are being stored for a while. If they are plated then the cleaning should be a 'polishing' so as not to actually remove the plating. Kitchen 'scotchbrite' is good for that. Polish the underside of the cable lugs too.
There is plenty of debate on the desirable current path but the bottom line is that you want the BMS to see the battery and the main current path terminal resistances to be low. Some argue that it is good for the BMS to be including the terminal resistances…. Yeah maybe but there shouldn’t be any problem with terminal resistance in the first place.

Use a small torque wrench for the bolts. It is easy to damage the thread in the terminal, particularly the aluminium one. Tightening torque numbers are out there somewhere or you can soon find a comfortable number… but be consistent .
As Coulomb has pointed out, contact resistance is an inverse function of contact force. i.e. tight bolts are good both mechanically and electrically. But to enable good force... Check your bolt length uses all the available thread to limit potential thread stripping.
Check thread in battery terminal is full depth. I usually run a bottoming tap into the terminal and air blow clean. Some terminals were made on Fridays it seems.
Take care not to rotate the terminals at any time by applying too much torque. I usually check the nuts are tight before starting as I have found 1 in 20 are loose, on TS and Winston at least.
When tightening the bolts, the usual hold the cable/lug or strap for reaction rule applies. Don’t require the battery/terminal to handle all the torque. (same when undoing)

The PCB will creep and crush in time so the spring washer is important but in itself is designed to control tendency for bolt to undo rather than actually maintain the contact force. Some folk use cone washers that apply more spring force. Just mentioning this as I usually use only spring washers and the assembly seems reliable.
Spreading the load with a flat washer is good around the PCB. That flat washer at the top of the PCB seems at risk of contacting surface mount components adjacent to the hole ? Take care with a socket on that negative terminal so it doesn't contact or damage PCB. I prefer to use hex head cap screws rather than hex bolts as the risk of slip/contact/adjacent damage is reduced. edit: i.e. Allen key head. Not a problem if you have a system with hex bolts though.

Keep in mind that the jointing compound is designed to be 'between' the metal faces and all excess should be wiped clear as the 'grease' of the compound tends to attract/hold dirt over time. Some of this dirt may in itself be conductive or corrosive. If you get squeeze out of paste on assembly then you used too much. Wipe it off. Use less on the next joint. Handling parts with greasy fingers (joining compound grease etc) is not a problem, but yes, skin acid/oil + time is less desirable.

I’m not a fan of the solid/layered copper straps , they can place large loads on the battery terminal in assembly and transport. I’ve seen terminal failures (broken plastic case around terminal) resulting. The braided straps are better. Having said that, a well strapped up battery pack and attention to strap ‘locked in loads during assembly’ is the next best thing.

Are you going to brush some conformal coating on the BMS PCB ? Spray may not be an option given the terminals.

Now, what is the magnetic reference ? I must have missed something. I tend to use s/s or zinc plated steel parts.
Last edited by acmotor on Sat, 07 Dec 2013, 07:09, edited 1 time in total.
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Post by 4Springs » Sun, 08 Dec 2013, 01:22

acmotor wrote:Some thoughts,
Great! I like thoughts.
acmotor wrote: You can use a tiny ! smear of a pure petroleum jelly like Vaseline on the bolt thread to control corrosion and provide lubrication for tightening.
What do you think of threadlocking compound? The provided bolts have a patch of dry threadlocker on them. On my current vehicle I used a small amount of low strength liquid threadlocker. I have had several of these bolts out since originally putting them in, and I'm quite happy with the product.
acmotor wrote:Is that a solid or layered strap ?
It is a 5 layered strap. It is bright silver, so I presume it is plated copper. They are shiny and new, so on your advice I will put them in sealed bags until I need them. One of the holes is elongated to allow it to be positioned to exactly the right spacing.
acmotor wrote: Check your bolt length uses all the available thread to limit potential thread stripping.
Hmm.. There is only about 1/3 of the bolt left after all that other hardware. I may need to buy some longer bolts.
acmotor wrote: That flat washer at the top of the PCB seems at risk of contacting surface mount components adjacent to the hole ?
The flat washer is close, but cannot contact anywhere it shouldn't. I just bought some more washers today which are thinner (smaller OD) still. The socket is a different matter though - in the couple I have tried I have found it difficult to keep it from the components. And you can't turn the BMS off! I like the idea of Allen key bolts, which is what is used on my current lead-acid batteries.
acmotor wrote: Are you going to brush some conformal coating on the BMS PCB ? Spray may not be an option given the terminals.
I have bought a spray for the boards, with the intention of masking the terminals.
acmotor wrote: Now, what is the magnetic reference ?
That was a clue as to what metal I was dealing with. So stainless steel is not magnetic, but zinc plated steel is. I have not come across faintly magnetic metals before (the washers are faintly magnetic), but I assume it is some s/s alloy.

Thanks guys, I'm the type of person who likes to spend some time now to save grief later on...

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Post by acmotor » Sun, 08 Dec 2013, 03:27

Ok, plated, 5 layered copper strap. That is better than a solid strap in flex and being plated should be ok between plates. Yep, keep the air off until fitting.

Interesting. Threadlock on the terminal bolts. I'd say a definite no but could be convinced otherwise. It would have to be a good argument though. Image Threadlocking if you had a bolt coming loose issue maybe but if you follow the reasoning that the best electrical connection to the battery will (apart from clean metal and jointing paste) be up to the clamping force supplied by the bolt. This wants to be as large as possible without thread stripping (or rotating the battery post).
A lightly greased bolt is mechanically the best option for that.... and the threadlock may not help with corrosion control.

Good to do your homework. Battery terminals are one item you want to set and forget. Image
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Post by acmotor » Sun, 08 Dec 2013, 03:31

Oh, you refered to a dry 'threadlocker'. Are you certain it was not a teflon paste deigned to seal air out of the bolt/terminal post area for corrosion control ?
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Post by Adverse Effects » Sun, 08 Dec 2013, 04:38

acmotor wrote: Oh, you refered to a dry 'threadlocker'. Are you certain it was not a teflon paste deigned to seal air out of the bolt/terminal post area for corrosion control ?


i think its threadlock as you can see it in the pic's and i have some bolts here they the same spot on the threads and its threadlock

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Post by acmotor » Sun, 08 Dec 2013, 04:40

So if it is thread lock, is there a good reason why ????
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Post by Adverse Effects » Sun, 08 Dec 2013, 04:49

lol my bolts are for a 1/5th scale RC car with a ICE 2 stroke in it so it vibrates like hell on earth but i dont know about the ones for the battery's but at a guess its to stop them loosening off as we all know that can be dangerous and damaging to the battery's

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Post by 4Springs » Sun, 08 Dec 2013, 13:05

Just my thoughts on threadlocker:
Yes, the supplied bolts have a spot of blue, dry threadlocker on them. I don't think I'll be using these bolts though, since I'll want longer bolts with Allen key heads on them.

I used the liquid threadlocker on my current vehicle just because it was what my gut feeling told me to do. I've worked on tractor implements, and know that nuts and bolts come undone in high vibration environments. Split washers help, but Nylock nuts work better. Threadlocker was what I came up with because I was using bolts not nuts.

Now that I've had it on the bolts for my current batteries, I can report that this threadlocker makes the bolts firm. A bit like Nylock, you cannot turn them by hand, but it doesn't take a lot more force than that. They do not lock tight (so to speak), they are just extra firm. When I've had a bolt off I've attempted to clean the compound off the thread with a wire brush before re-applying and putting the bolt back on. The product I used was Cyberbond 7243.

Having said that, I don't think that the vibration in the car can be compared with a tractor implement! After all, the cells have only a little bit less suspension than I do in the driver's seat. It may be that the belts and braces ideology is not required in this case, and I can just stick with the split washer. It sounds like a run over the pack with a torque wrench periodically might be a good idea too, from what acmotor said about circuit boards compressing.

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