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Learning how to build Lotus Seven replicas...together!
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PostPosted: June 5, 2020, 3:03 am 
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Joined: February 9, 2015, 4:15 am
Posts: 13
Hi Martin
My families from Leith - I went to school in Perth and Uni in Glasgow

Cooling - there is very very little actual energy flow - the main thing that the cooling is doing is equalising cell temperatures

I don't have a radiator on my system - I flow coolant past my controller and then through the batteries and back to the controller

The highest temperature I have seen on a scorching hot day when I was drag racing was 27C
I may be different if you live somewhere hotter!
I am flowing the water through two identical setups in paralel - don't see how I would get signifigantly different flows

BMS
I have a cheap BMS
http://www.evdl.org/pages/battbridge.html
Which is actually fiendishly cunning!
It operates by comparing the voltages across each half of the battery - if one half is different to the other it lights an LED
Back when I was using Headway cells and had lots of failures it caught them every time
Unlike a more sophisticated BMS this is actually working and checking when I am loading the cells - my battery current peaks at 1200 amps

Other than that I just check the cell voltages every year or so - all within 14 milliVolts when I checked last - I check at "empty" and at "Full"
I'm only using from 3.5 volts to 4.05 volts - being a bit conservative

Range - my aerodynamics are poor (awful) - my range at 100 kph is only 50 km - I have 14 kwh - not the whole 16 kwh

Charging - I use a BRUSA charger - it's very good but I have set it to 8 amps input - this is because I decided I may need to charge from some farm shed somewhere - most power sockets are 230v/12 amps
With only 8 amps and 230v it takes just over 7 hours for a full charge

The drag races don't take much out of the battery but we had a tarmac autocross just before the virus nonsense
These are usually slow speed events - the straights are very short to keep speeds down
This one had some fast sections - up over 90 mph
I only had enough power for the "indian file" and five timed runs - I drove for two and my son drove for three - not enough left for my third run
Great fun! - the car went superbly - the drivers less so - we both murdered some cones


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PostPosted: June 9, 2020, 1:18 am 
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Joined: February 5, 2010, 12:48 am
Posts: 314
Location: San Diego
duncanmark wrote:
Hi Martin
My families from Leith - I went to school in Perth and Uni in Glasgow

Cooling - there is very very little actual energy flow - the main thing that the cooling is doing is equalising cell temperatures

I don't have a radiator on my system - I flow coolant past my controller and then through the batteries and back to the controller

The highest temperature I have seen on a scorching hot day when I was drag racing was 27C
I may be different if you live somewhere hotter!
I am flowing the water through two identical setups in paralel - don't see how I would get signifigantly different flows

BMS
I have a cheap BMS
http://www.evdl.org/pages/battbridge.html
Which is actually fiendishly cunning!
It operates by comparing the voltages across each half of the battery - if one half is different to the other it lights an LED
Back when I was using Headway cells and had lots of failures it caught them every time
Unlike a more sophisticated BMS this is actually working and checking when I am loading the cells - my battery current peaks at 1200 amps

Other than that I just check the cell voltages every year or so - all within 14 milliVolts when I checked last - I check at "empty" and at "Full"
I'm only using from 3.5 volts to 4.05 volts - being a bit conservative

Range - my aerodynamics are poor (awful) - my range at 100 kph is only 50 km - I have 14 kwh - not the whole 16 kwh

Charging - I use a BRUSA charger - it's very good but I have set it to 8 amps input - this is because I decided I may need to charge from some farm shed somewhere - most power sockets are 230v/12 amps
With only 8 amps and 230v it takes just over 7 hours for a full charge

The drag races don't take much out of the battery but we had a tarmac autocross just before the virus nonsense
These are usually slow speed events - the straights are very short to keep speeds down
This one had some fast sections - up over 90 mph
I only had enough power for the "indian file" and five timed runs - I drove for two and my son drove for three - not enough left for my third run
Great fun! - the car went superbly - the drivers less so - we both murdered some cones


Duncan, thanks so much for sharing all this information. It really is very helpful. Interesting to note the lack of radiator. I'd say our upper ambient temp is around 35 C so I am thinking of incorporating small quadbike radiators, one for the battery pack and one for the inverter/motor (combined in the Tesla sdu). At the low end, I doubt the car would be used below 12C so not going to include the heating element.

On the voltages, you are quite conservative. Are these batteries good for a wider range, say 3.0 - 4.1 V? I'm keen to know because this will be a tarmac autocross car and I'd like to get 8 runs in. Average speed around 55mph (80 max for short duration). Runs 40 - 80 secs.

I went to Uni in Edinburgh. Leith was going through a serious revamp then!
Cheers
Martin


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PostPosted: June 10, 2020, 4:07 am 
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Joined: February 9, 2015, 4:15 am
Posts: 13
Hi Martin

On this page there is a reply from Yabert which contains a voltage/charge discharge he did at 1/8thC

https://www.diyelectriccar.com/forums/s ... 01p17.html

Looking at that I don't think there is anything useful left below 3.4 volts and above 4.2 volts - so you may be able to get a wee bit more maybe another 10% ??

If you have the whole battery then you will have about 15% more energy than I do

That event where I ran out of power was fast - and long

Eight runs at a lower speed on a shorter run.........should be OK

Just have to suck it and see


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PostPosted: June 11, 2020, 12:49 am 
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Joined: February 5, 2010, 12:48 am
Posts: 314
Location: San Diego
duncanmark wrote:
Hi Martin

On this page there is a reply from Yabert which contains a voltage/charge discharge he did at 1/8thC

https://www.diyelectriccar.com/forums/s ... 01p17.html

Looking at that I don't think there is anything useful left below 3.4 volts and above 4.2 volts - so you may be able to get a wee bit more maybe another 10% ??

If you have the whole battery then you will have about 15% more energy than I do

That event where I ran out of power was fast - and long

Eight runs at a lower speed on a shorter run.........should be OK

Just have to suck it and see


Thanks Duncan. Looks like with the whole battery and the fact it is the Gen 2 I should be okay. Was toying with the idea of installing a battery on my trailer. I wonder if a DC charge can be made from one battery to the next? Then perhaps track days might be an option too. That's for another day in the distant future.


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PostPosted: February 3, 2021, 3:55 am 
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Posts: 13
Ayup Martin

How are you doing??

Any progress?


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PostPosted: February 3, 2021, 8:25 am 
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Joined: January 1, 2012, 12:44 pm
Posts: 588
Location: Boise, Idaho
Hey Duncan,

"Just have to suck it and see."

This was way out of place in this thread, but it brought a big smile to my face. For the youngsters, this is a quote used frequently in a book on the tuning of weber carbs that I used to use back in the seventies. :cheers:
Ron


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PostPosted: November 6, 2021, 9:41 pm 
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Location: San Diego
Well, progress has been really slow. I guess motivation diminished during last year's COVID craziness, and the summer was very hot. Anyway, back at it now, and the chassis looks like this:
Attachment:
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PostPosted: November 6, 2021, 9:42 pm 
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Location: San Diego
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PostPosted: November 6, 2021, 9:56 pm 
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Joined: November 21, 2019, 12:09 am
Posts: 151
Location: Wilson, NY
Martin,
It’s great to see you back at it. I’m looking forward with great interest to see how your project comes together.
Thank you,
Eric

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MGiata current build here: https://www.mgexp.com/forum/mga-forum.2 ... n.3898051/


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PostPosted: November 6, 2021, 10:00 pm 
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Location: San Diego
duncanmark wrote:
Ayup Martin

How are you doing??

Any progress?


Sorry Duncan, it's been a while. Been putting up some photos on social media too, which I think you're part of (EV Conversions)?

Hoping to get through some more of the build this winter, but there are new distractions, such as track days, for my Miata/MX5 build, aka "The RP7".

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PostPosted: November 6, 2021, 10:01 pm 
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Location: San Diego
ohmite wrote:
Martin,
It’s great to see you back at it. I’m looking forward with great interest to see how your project comes together.
Thank you,
Eric


Thanks Eric. I have huge levels of anxiety knowing I have all the parts in hand to finish this thing, just not the time! Slow and steady wins the race I guess!


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PostPosted: November 7, 2021, 2:50 pm 
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Joined: July 7, 2011, 12:17 am
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Location: Oregon City, OR
Subscribed - I don't know how I missed this thread. Looking forward to seeing this come together!

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PostPosted: January 17, 2023, 11:39 pm 
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Joined: February 5, 2010, 12:48 am
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Location: San Diego
If anyone is interested, progress is being made on the Cyber7:

https://www.facebook.com/groups/3125150271029774/


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PostPosted: January 18, 2023, 11:34 am 
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Location: Carlsbad, California, USA
Lots of nice workmanship there, Martin. How close do you think you are from having it functional?

Cheers,

Lonnie

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: January 18, 2023, 12:21 pm 
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Location: San Diego
Hi Lonnie,
If all goes well, the motor should be running in the next month. Then I need to weigh the whole car to get shocks built to spec. Hopefully rolling this summer.
I think it must have been 12 or 13 years ago you came to visit my first build!
Looking forward to seeing yours running.
Martin


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