Split pack battery charging...

[jonescg]

Hi all,

So I will be running with a high voltage pack in both the eCRX and the electric race bike. Both vehicles will use a maximum charge voltage of 705 volts.

in the CRX: 170 cells at 4.15 V max
in the race bike: 168 cells at 4.20 V max

Now, most companies don't make single chargers capable of going this high. So an option is to split both packs and charge at 352.5 V a side. I would like to mount them inside the car so it can warm the car up on cold mornings I stand by the TC charger as being a sold piece of equipment, so a pair of 2 kW chargers to do the pack in halves sounds good.

Until you start tripping out circuit breakers . This setup will put a 17 amp draw on a 240 V circuit. To my knowledge most household circuits are only 15 amps max. So that rules out single phase charging. Oh, and I will not be charging half a pack at a time - that's just asking for a user-derived failure!

So for the CRX, should I get a three phase, 32 A, 5 pin plug made up with a J1772 plug on the other end? It means I can't opportunity charge from a 10 A GPO, or even a 15 A socket. And getting a big box like that installed at the house won't be cheap. At least several car parks around Perth have 24 kVA 3 phase sockets...

Also, for the race bike, which will have its chargers off-board, I will have to devise a 4 pin 705 V DC plug which is split between the pack halves and is finger-proof. Can anyone think of a good option here?

Thanks in advance,

Chris

[Renard]

I have ordered two TC chargers, each 2kW set to 400V for my pack. They can be paralleled, and in fact the price of two at 2kW is cheaper than one at 4kW. I will also gain flexibility. Normal household circuits are rated at 20A, and are fitted with 20A circuit breakers -- or they should be. (If you've still got fuse wire in ceramic holders -- get up to date.)
A 20A CB will trip at infinity at 20A and at shorter times for higher currents. So a standard circuit is good for 20A. By having two 2kW chargers, each drawing under 10A, you could put them both on the same circuit, or one each on different circuits, and not have to worry about special plugs etc. (Once you have an appliance that goes over 10A, it needs a dedicated circuit.)
If you want to use three phase, why not consider getting three chargers, each of one-third the required voltage?

A four pin plug is easy to source, that's what three phase power usually requires -- without the neutral. Try schnap.com.au for a good price.

[jonescg]

I paralleled three TC charge outputs for trackside charging of Voltron, but this was only at 117 V. Ideally I would put the outputs in series, but I don't think it's recommended, hence the split pack idea.

OK, so would the power demands of two 2 kW chargers be OK for any one circuit? Charging in wintertime might be risky as I don't know which circuits are free of other appliances.

As for the race bike, I will look into a panel mounted 3 phase socket. I realised it only needs to be 3 pin, as one of them will be shared by both chargers.   

[weber]

We've had to solve all these problems with the MX-ϟ. We have 228 cells at 3.65 V max.

As we mentioned when we saw you at the Ipswich raceway, finding anything with more than a 600 V rating (particularly a 600 V DC rating) is very difficult. But if you use two separate connectors, each only needs to be rated for half the pack voltage.

We use the SBS50 finger-safe Andersons. There is also an SBS75x but they are harder to get and they don't come in the differently-keyed colours that prevent people plugging the wrong things together (like two half packs, eek!).

Data here:
http://www.andersonpower.com/products/m ... e-sbs.html

Buy here:
http://andersonpower.com.au/store/index ... word=sbs50

Don't assume that a 2 kW charger will only draw 8.5 A from the 240 Vac. There's efficiency and power factor. I think you'll find it's close to 10 A. So while a single circuit may be 20 A that doesn't allow for anything else to be running on that circuit at the same time as two chargers, except maybe in short bursts. And if wiring is old, you're asking for trouble. It may never have been subjected to such a high load for such a long time.

We are using two TC chargers, charging half-packs. But most places have at least two separate 240 Vac power circuits, so we plan to plug one charger into each. To find two outlets that are on different circuits, turn off the circuit breaker for one circuit then find one outlet that works and one that doesn't -- usually widely separated e.g. upstairs/downstairs, north/south or east/west. Then turn it back on.

In cases where we only have one 10 A outlet we can in theory parallel the two half packs and charge them from a single charger. We haven't tried this yet. It could be tricky to balance. Another option would be to switch the one charger between the two packs at half time, assuming you know how long you've got.

But adding a 3-phase-to-two-single-phase adapter to the kit is also a good idea.

Next you'll be asking about fuses and contactors with a suitable combination of DC voltage and current rating.

[weber]

It's not a good idea to take a plug or socket that is standard for one voltage and type of power (AC vs DC) and use it for another voltage or type. That's just asking for trouble. In fact it is probably illegal in the case of standard 240/415 Vac plugs and sockets. You certainly can't use them for DC in standalone power systems, as covered by AS4509.

The other problem is that, with a charger and a battery, both sides need to be finger safe. I know the charger has a relay, but I wouldn't trust it. Fortunately we have the Anderson SBS solution.

[Renard]

I misunderstood your 4-pin plug requirement, I thought it was for an AC supply. For DC you're going to have to search.

Every house must have at least two power circuits according to AS3000, and it is certainly prudent to spread the load. But good quality wiring should cope with 20A.

[coulomb]

In cases where we only have one 10 A outlet we can in theory parallel the two half packs and charge them from a single charger. We haven't tried this yet. It could be tricky to balance.

Or alternatively, just program the two chargers to only charge at half current maximum, and plug both chargers (on separate pack halves) into the same outlet with a double adapter, or better yet two outlets on the same circuit.

We haven't figured out an effortless, idiot proof user interface for this as yet.

[ Edit: separate split packs -> separate pack halves ]

[weber]

Or alternatively, just program the two chargers to only charge at half current maximum, and plug both chargers (on separate pack halves) into the same outlet with a double adapter, or better yet two outlets on the same circuit.

Oh duh! Yeah. That's the right way to do it when you only have one 10 A outlet. Forget about parallelling the half-packs. I remember now Jeff Owen pointing that out.

The user interface (UI) might be a pot connected to an analog input on the Driver Controls Unit (the thing that listens to the BMS and sends current-setting commands to the chargers). This pot could be marked "Charge rate" and you could back it off a bit every time the circuit breaker tripped. Or it could just be a switch marked "Half charge rate".

Don't the non-CAN-bus versions of the TC Charger have a place you can connect such a pot?

[jonescg]

Interesting ideas. I wanted a 4-pin plug on the race bike so it was impossible to only charge half the pack.

I think for the car I won't have any trouble coming up with a solution since the chargers will be onboard. Even if I have to use a 32 A single phase. Although a big 32A three phase plug would give me some options.

[weber]

The SBS-50s have two holes for M3 bolts. You could bolt two together, with a plastic spacer between for extra voltage isolation. The same bolts can hold the ones on the bike in place.

How will you ensure the two half packs are isolated from each other before charging. One (low mass) way would be to use the same Andersons to feed the power to the bike. So you would have to pull out the plug that goes to the motor controller contactors to be able to plug in the charger.

[Johny]

How will you ensure the two half packs are isolated from each other before charging.

He doesn't have to provided the chargers have isolated outputs.

[jonescg]

I was thinking of doing that (using the same plug for power as for charging) but I also want the added safety feature of not being able to access power from the pack unless 12V was fed into it, closing the main contactor. I would like the option of being able to charge without leaving the bike switched 'on'.

The andersons, even with the fingerproof option, look a bit ratty. Sure, compared to Voltron I, anything will look professional . Maybe I could use a 62196 style charger outlet and receptacle?
http://www.wholesale-electrical-electro ... 24587.html

[Tritium_James]

That's the Menekes euro charge plug, but it's for the AC side of things, not DC to your pack.

[jonescg]

I know, but as a one-off charge plug and socket arrangement for the race bike it's not so bad. I would only be putting 352.5 V DC through it at no more than 6 amps. If it can't handle that... Hmm.

[weber]

How will you ensure the two half packs are isolated from each other before charging.

He doesn't have to provided the chargers have isolated outputs.

I already know the chargers Chris wants to use have isolated outputs, but whether it is safe to leave the two half packs connected as a 700 V pack during charging still depends on what the charger's isolation voltage rating is. It can be hard to find such specs, so the most we can safely assume is the greater of the peak AC input voltage (340 V) and the maximum output voltage (400 V). So 400 V overall.

Also, these chargers have their outputs isolated from their power inputs and their cases, but stupidly not isolated from their control inputs! We've added isolation to the control inputs on ours (using optic fibre).

[Johny]

Also, these chargers have their outputs isolated from their power inputs and their cases, but stupidly not isolated from their control inputs! We've added isolation to the control inputs on ours (using optic fibre).

Ouch! Wow! Point taken.

[weber]

I was thinking of doing that (using the same plug for power as for charging) but I also want the added safety feature of not being able to access power from the pack unless 12V was fed into it, closing the main contactor. I would like the option of being able to charge without leaving the bike switched 'on'.

That's very wise. That just means that the main contactors should come between the battery and the plug. I say "contactors (plural)" beacuse there should be one set of contacts for each end of each half-pack, because they are floating and (I presume) you have no way to detect a fault to chassis.

I find that EVers commonly confuse the "main" contactor(s) with the "motor controller" contactor. According to AS3000, for an isolating device to be considered "main" it must isolate the entire installation* (in this case controller, charger and possibly DC-DC converters) from some source of supply (in this case the battery). [* excluding essential emergency equipment e.g. fire-fighting systems]. See the schematics at the end of this post
viewtopic.php?title=weber-and-coulombs- ... 093#p34093
For charging, main contactors must be on but motor controller and precharge contactors most definitely off. Microswitches will detect the presence of the charging plugs or cables and disable the controller and precharge contactors at the same time as enabling the main contactors, without needing the ignition key.

Looking at our hazardous-voltage schematics again makes me realise that our proposed 750 V circuit has exactly the arrangmenet that I was arguing against with Johny. So it looks like we need yet another contactor (between the two half-packs), or some specs that say the TC chargers are insulated to 830 V continuous.

The andersons, even with the fingerproof option, look a bit ratty.

I guess I don't share your sense of aesthetics or its importance in this case, but I do note that the Andersons are not waterproof, so they would need to be hidden under a waterproof cover of some kind anyway.

[jonescg]

Ratty might not be the best word, but yeah, having the charge receptacle on the battery pack not protrude would be good. I have a diagram of what I have in mind but photobucket seems to be chucking a spaz. I will upload my schematic once they solve their '324' error.

[woody]

Anderson Power Pak help at all?

It has panel mount for 2-10 PP45A connectors.

[jonescg]

The 6 pin plug would simply be to share the current across the two chargers. Whether or not this is a fancy HV rated plug or a bunch of Andersons, I don't know yet. But in the interest of safety I would need at least two contactors - one for the drive and one for charging.

splitpackchargesystem.JPG (39.11 KiB) Viewed 1814 times

[Tritium_James]

Not necessarily - why can't the motor controller, DC/DC, etc be powered up while you're charging? The DC/DC can keep the 12V battery full that way, making sure your BMS, charger controller, etc don't run it flat.

[jonescg]

It's just another failsafe really. I'm trying to come up with the most space efficient means to isolate the high voltage from the user under idle, charging and discharging conditions. Within reason of course - I'm not planning on developing an ECU for the race bike. Unless I really have to.

[weber]

Anderson Power Pak help at all?

It has panel mount for 2-10 PP45A connectors.

Ooh! Those are pretty. And when I went to look at them I saw these
http://www.andersonpower.com/products/s ... ctors.html which might be even more like what Chris has in mind for a DC charge port. Although it seems the touch-safe/finger-proof ones may be limited to the 45 A finger-proof power-pole inserts that have a contact resistance 2.6 times that of the SBS50. They would be fine for charging, but you may not want to put the controller current through them.

[weber]

Not necessarily - why can't the motor controller, DC/DC, etc be powered up while you're charging? The DC/DC can keep the 12V battery full that way, making sure your BMS, charger controller, etc don't run it flat.

Hi James, I assume you're responding to something I wrote. It would be good to know what, as you may have misinterpreted it. I didn't say the DC/DC should be prevented from operating while charging. I agree it should be operating. You can even run the cabin heater if you want. But why would you ever want traction power to the motor controller while charging? It sounds like asking for trouble. Not only the risk of drive-off, which might be prevented by other means, but the bus caps etc. will be exposed to higher voltages than they otherwise would.

If your DC-DC is connected such that you can't isolate the motor controller without isolating the DC/DC then you have a design problem.

[jonescg]

I have emailed Nancy Loo about the isolation, and recommended charging wiring diagrams for the split-pack idea. Her engineer was away, so I will have to wait. She assured me everything was isolated from the HV output.

Sorry if things are getting confusing between projects here - I will be building two EVs, one will have lots of room for contactors, precharge resistors, fail safes and the like. The other is a balls-out speed machine with barely enough room to swing a cat.

The race bike will need the most design thought as space is at a premium. I do like the idea of charging and discharging through the same battery lead, as it instantly disconnects the motor drive as you go to charge. It does however need more fancy contactors and precharges, which are also quite space intensive.

Maybe the charge receptacle can be finger proof, but not switched through a contactor to save on space (that is, full pack voltage is accessible if you are dumb enough to probe deep enough for it).

This would all be so much easier if a single charger can be found which gives 705 V and no need to split the pack...

Edit to add:
http://www.currentways.com/ProductView.aspx?PID=1001
"without the need for a centre-tap".

I like it It means I can park the car right next to the race bike and charge it up like I was getting a jump start