Renard's BMW

Post up a thread for your EV. Progress pics, description and assorted alliteration
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Post by coulomb » Fri, 22 Nov 2013, 02:43

Renard wrote: The fan has 3 1/2 times the capacity of the existing one, but runs from 48V. That calls for another DC/DC converter, albeit one with a smaller output than the existing 12V, 450W Meanwell, for example a 48V, 150W type.

If you have trouble finding one, you might consider a 12 V to 48 V converter. Sure it's inefficient to go from pack voltage down to 12 V and back up to 48 V, but it might be a lot easier to find, and likely cheaper too. I'm assuming you don't need the whole 150 W for just a fan, but if it's a monster, maybe you do. I suppose that's why it runs at 48 V, to keep the current sane.

Of course, that assumes that you have power to spare on the 12 V side of things, including spare average power from the pack to 12 V converter.

The other thought is a radiator fan intended for an ICE. I assume that they are fairly powerful. Thus avoiding the extra DC/DC altogether.
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Post by weber » Fri, 22 Nov 2013, 03:32

An option we considered at one time was to put a fan on each side of the motor at about the middle of the side, blowing into the fins. But we have brackets there now, holding the vac pump, PS pump and aircon compressor.

What motor temperatures are you seeing? What is your motor's insulation temperature rating?
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Post by weber » Fri, 22 Nov 2013, 04:05

From Wikipedia:

"The temperature class indicates the temperature of the wire where it has a 20,000 hour service life."

"Insulation does not suddenly fail if the hot-spot temperature is reached, but useful operating life declines rapidly; a rule of thumb is a halving of life for every 10 °C."

I think it was Johny who pointed out this sort of thing. In an industrial application the motor may be running 24/7. In an EV the motor is unlikley to run even 2 hours a day. In that case 20,000 hours would be 27 years. So it wouldn't be a problem if it ran at its rated temperature e.g. 155°C, the whole time.
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Post by Johny » Fri, 22 Nov 2013, 14:19

Sorry to hear about the minor glitches Renard.
If it's any help I have a 172mm circular fan inside the motor fan cowling. It's a 240VAC (they couldn't supply 12VDC at the time) 72W and runs off a $20 chinese 12V to 240VAC inverter. The only time it comes on is in stop-start slow traffic (direct drive) and generally goes off again after about 5 minutes of normal driving. The controller runs the relay driver and it's set to come on at 60 degrees winding temp - I don't practise what I preach and don't like the motor getting too hot.

I'm pretty sure my current fan is NOT rated for IP65 so my plan is to replace it with a PAPST 6412 when it fails (or a PAPst6424 which are WAY cheaper ($30 Rockby) and a 12V to 24V boost converter ($6 eBay) - and do away with the inverter. Having just gone through winter - it looks like it's not going to fail any time soon. The front of the motor doesn't appear to get much splash.

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Post by Renard » Fri, 22 Nov 2013, 16:52

weber wrote: From Wikipedia:

"The temperature class indicates the temperature of the wire where it has a 20,000 hour service life."

"Insulation does not suddenly fail if the hot-spot temperature is reached, but useful operating life declines rapidly; a rule of thumb is a halving of life for every 10 °C."

I think it was Johny who pointed out this sort of thing. In an industrial application the motor may be running 24/7. In an EV the motor is unlikley to run even 2 hours a day. In that case 20,000 hours would be 27 years. So it wouldn't be a problem if it ran at its rated temperature e.g. 155°C, the whole time.


The motor has the F rating for 155deg max. The issue is not that I mind running the motor hot, but that going up a significant hill at even modest speed can result in the WS cutting back the power, and then even sometimes cutting it off altogether. This is not a happy feeling, waiting by the roadside for the motor to cool a bit.

Not having the expertise to tap into the CAN bus data to monitor the temperature, I had glued into the motor a second thermistor. I have been using this as a simple switch to turn on the fan for temperatures over about 45deg., but I could certainly use this signal to report actual temperatures with the DAC output of a PIC micro. Up till now, I haven't known what the actual motor temperature was, except by putting the meter across the thermistor signal and referring to the thermistor's performance sheet.

I do know though, that I need more cooling and that's why I've ordered the 2218F/2TDH4P ebm-papst fan and a 48V 150W Meanwell converter. (See the papst catalogue Compact_fans_2011_EN_n.pdf Page 70 at http://www.ebmpapst.com.au/en/products/ ... ctfans.php )

This fan advertises itself as speed-controllable with a PWM input which should be useful as at full speed it will make significant noise, and its full output will not be needed most of the time. (As I know from from my current driving experience with the existing fan.)
Just how much improvement in cooling I can get I don't know, but it's got to be better.
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Post by Renard » Fri, 22 Nov 2013, 17:05

Johny wrote: The only time it comes on is in stop-start slow traffic (direct drive) and generally goes off again after about 5 minutes of normal driving. The controller runs the relay driver and it's set to come on at 60 degrees winding temp - I don't practise what I preach and don't like the motor getting too hot.


Johny, I think that your driving situation differs markedly from mine, being basically urban. My driving is mostly at continuous speeds of at least 80km/hr or more, and then on meeting a long hill on a major road, one doesn't want to crawl up it at low speed to prevent the motor getting too hot.

Like you, my fan is well protected with a battery box just forward of it, and the front cross-member just beneath it.
The fan I've ordered is MUCH more expensive, but hey -- how much have I spent already? No point in skimping.
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Post by weber » Fri, 22 Nov 2013, 19:19

Renard wrote:The motor has the F rating for 155deg max. The issue is not that I mind running the motor hot, but that going up a significant hill at even modest speed can result in the WS cutting back the power, and then even sometimes cutting it off altogether. This is not a happy feeling, waiting by the roadside for the motor to cool a bit.

So what ramp and cutoff temperatures have you set in the WaveSculptor configuration for your motor? See page 11 of the WSconfig manual
http://tritium.com.au/wp-content/upload ... Manual.pdf

We have 140^C and 150^C. So far we haven't seen more than 100^C, this was from driving up Mt Coot-tha at 50 km/h (the speed limit).

I'm assuming you have the Tritium CAN/Ethernet bridge. If so, you can display the motor temperature, among other things, on a laptop, using the Telemetry window of the same software (WSconfig).
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Post by Renard » Fri, 22 Nov 2013, 20:53

weber wrote:
So what ramp and cutoff temperatures have you set in the WaveSculptor configuration for your motor?

We have 140^C and 150^C. So far we haven't seen more than 100^C, this was from driving up Mt Coot-tha at 50 km/h (the speed limit).

I'm assuming you have the Tritium CAN/Ethernet bridge. If so, you can display the motor temperature, among other things, on a laptop, using the Telemetry window of the same software (WSconfig).


Ramp from 140deg; cut-off at 155deg. My car is quite a bit heavier than yours at 1590kg plus me, driver at 60kg. How steep is Mount Coot-tha?

Alas, I don't possess a laptop, only a mains computer. And my wife's Macbook Air lacks an ethernet port, so I can't connect the bridge.
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Post by weber » Fri, 22 Nov 2013, 22:48

Renard wrote:Ramp from 140deg; cut-off at 155deg. My car is quite a bit heavier than yours at 1590kg plus me, driver at 60kg. How steep is Mount Coot-tha?
It climbs 190 m in 2.4 km. I concede that you really do need that fan. Although if it was still a problem getting up your big hill, you could maybe afford to bump both of those settings up 10 degrees, on the basis that time spent at 165degC only counts for double the time spent at 155degC.
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Post by Renard » Mon, 31 Mar 2014, 16:02

Well, we have moved house after 19 years. I knew we had to do it, as to leave it any longer would mean we'd be too old to consider it, and we'd be just stuck in a place we had finished with. But the effort has been huge, and of course the BMW has been relegated to a very low priority, what with preparing the house for sale and then all the packing and, of course, the emptying out of the shed.

As I had written earlier, when the battery boxes were removed, I installed the larger fan. This required chopping into the existing cowling.
The new, bigger fan is 200mm in diameter and has a nominal maximum flow of 1220m^3/hr. It runs off 48V. A new, 48V 150W DC/DC converter has been installed in the boot under the rear parcel tray. Testing the fan with its sensor lead held at 5V (a full-on situation) resulted in current of 4.75A. (228W) Grounding the sensor lead switches it off.
It is being driven with a 2kHz PWM signal to the base of a NPN transistor whose collector, held at 5.1V with a zener diode, connects to the fan sensor lead. I've set up the PIC micro to read the voltage on a thermistor on the motor windings -- a thermistor additional to the one for the Wavesculptor -- and to set the mark/space ratio accordingly. The fan is set to come on at about 40deg and increase in 20% steps to be full on at 125deg. It's pretty loud at full whack.

Image

Image


Just to get the car going, I repaired the wiring from the encoder that had fouled the fan, put everything back -- and still no go. So out came all the boxes again and I did what I should have done before: put the digital scope on the encoder outputs. One channel was dead, due probably to V+ shorting to the collector with the chewed wires. So out came the motor and a new encoder installed. Rather unnecessarily I also removed the clutch, and then realised I didn't need to dismantle the whole motor just to get the encoder in its end-plate off.
All was re-assembled and I then knew I had put the clutch disc back in the wrong way round -- some vibration in the transmission resulted although the car was able to be moved. The message was loud and clear: stop trying right now!The removalists were coming in a week and I just put the car in its existing state onto the car-carrier truck for transport down south.

Unfortunately, something happened on the way down here and the car wouldn't start to unload it from its truck. On looking into it, I saw that a pre-charge resistor was split, so no pre-charge and consequently the main contactor would not be allowed to close.
How did the carriers manage to achieve this fault? I had left clear written instructions on how to drive the car.
They must have managed to switch on the ignition with the accelerator depressed while simultaneously somehow putting it into gear. I'm amazed at the unconscious creativity of others in generating faults in one's equipment. And the lesson, I suppose, is to work harder to make things foolproof.

In fact, some time ago I achieved a similar result, shattering a pre-charge resistor, by driving the WS from the computer config. software whilst forgetting to close the main contactor. The high current draw requested by the WS was sufficient to destroy the resistors.
I can draw a couple of conclusions: firstly, the button-style bi-metal cut-outs beneath the resistors are ineffective in preventing failure as they are much too slow to respond to high current episodes.
Secondly, I need to prevent the WS from drawing current until the main contactor is closed. I can arrange this by taking a signal from the contactor control circuit (the collector of the transistor in this circuit) and passing it to Pin 7 of the DCU, this pin being the brake signal input. When this pin goes high, the DCU disallows WS current draw.

The house we are currently renting, while very pleasant, unfortunately lacks a sizeable shed. I have negotiated the use of a suitable shed nearby in which to work on the car.
The effort of moving house brought us down with illness and we are slowly recuperating. And very slowly getting back to dealing with the car. Last week I re-registered it, and drove it round to its new workplace.

To be continued -- slowly!

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Post by Renard » Mon, 31 Mar 2014, 16:05

On another matter, I see that Weber has finally succeeded in having Tritium increase the WS rpm report from 5Hz.
If this appears in a new firmware update, it might cure the issue I experience whereby jamming down the accelerator produces a big hiccup from the WS. At present I simply ensure that I don't do this.

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Post by weber » Mon, 31 Mar 2014, 16:55

Hi Renard. Great to hear from you. Sorry to hear about your trials and tribulations of moving. Good work on the fan.
Renard wrote: On another matter, I see that Weber has finally succeeded in having Tritium increase the WS rpm report from 5Hz.
If this appears in a new firmware update, it might cure the issue I experience whereby jamming down the accelerator produces a big hiccup from the WS. At present I simply ensure that I don't do this.

Can you give more detail on what you mean by "a big hiccup" here. Perhaps in less pediatric and more engineering terms. Image We may have an easy software solution for you and it may not require the faster velocity telemetry (except possibly to datalog the nature of the problem).
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Post by Renard » Mon, 31 Mar 2014, 22:35

weber wrote: Can you give more detail on what you mean by "a big hiccup" here.


It's like flooring the accelerator on a petrol car: it gasps and then leaps forward.
Similarly, with the WS, there is a momentary loss of power before the current kicks back in, the transmission goes 'clunk' and the car then jumps forward.
It does this at low revs too, and also when I set the regen. slider pot to zero, so I don't think it's an artefact of the special regen. software code.
(Pardon my terminology: 'gasps', 'kicks', 'clunks', 'jumps'.)

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