Fresca still looking for any reason to not go turbo

 

Update : Major changes taking place.
A few months back I had an unfortunate actual 'spanner in the works' experience. I was changing a wire over from one side of the on/off relay to the other when my spanner touched the side of the enclosure and .........zap. Discovered later after reassembling everything that my charger was toast. So .......... a pivotal moment . Do I just buy another charger and stick with these high maintenance batteries with a cantankerous charger or ............. UPGRADE?!
So:
Have ripped out the Lipo batteries, the charger and all the wiring.
Started over using an LTO battery pack I've made up myself and a new charger . Both have gone into the boot ...total weight of batteries+BMS+box+tray+charger is approx. 17Kg.
I've managed, after many hours of utter frustration, to get the BMS functioning and successfully charged the batteries.
Now to finish wiring the supply to the speed controller and then ....test!

 

First day of tests: After two days of tearing my hair out ( what is left) I finally got the BMS/charger/ESC combo working as it should.

Upsides:
Holding higher voltage and amps, therefore holding more boost for longer = moa powa baby!!!! Virtual dynos to come.
Batteries last a lot longer
No more need to partially discharge batteries.
New charger is now 'hands free' just hop in and drive .... no more buttons to push.
Batteries happy in all ambient temperatures.
Performance is WAY more consistent now- previous logs with Lipos were in 'best case' conditions. This setup rocks in all conditions.

Downsides
Added weight to rear approx. 17kg all up
Took up space in boot ............. about as much as a normal battery would take up.


Overall : absolutely ecstatic with the setup ...so glad I did this upgrade!

 

Note the numbers for voltage and current .... just over 10kw total power!

 

Does it seem like the guesstimations may be ballpark? Nice to know if they was on the right track for later knowledge, or if I should just bin the Excel sheet

 

I'm not at 5psi so couldn't say.
I may have jumped the gun a bit with my "moa powa" above. Virtual dyno actually looks about the same as it did with last setup. Was excited to see 45V at the battery at full load (vs 40 previously). Might be dropping some voltage on the way to the front from boot ....

 

It’s often wise to have a capacitor close to the terminals of controller, as it brings down the impedance(“AC resistance”) of battery supply. Even if the wire are large enough to carry the DC current, length of them introduce an inductor. Inductors increase impedance with frequency, thereby creating short voltage drops at controller when current change rapidly. This can cause controller to under perform. If your controller is close to the battery with short wires, the internal capacitors of controller should normally suffice.

 

Great point.
I had a capacitor close initially (150,000 microfarad) and it was causing big issues due to it creating a 'short ' . This not only welded my relay shut but messed with the battery BMS. I researched on how to make it charge more slowly but it all seemed a bit too complicated for me so I took it out. It was only then that everything started working properly.
Edit : I just ordered a smaller capacitor (66,000) and a larger relay. I read in instructions for BMS that I can adjust short protection to suit so hoping I can get a combo that works without the need for a slow charge circuit.
I could put the capacitor on the other side of the relay but am concerned that this would leave it in a charged state when engine is off .... Is this a valid concern?
I did have the cap post relay such that it discharged via the ESC every time engine is shut down. I also have a 250A circuit breaker at the battery so this might get tripped as well.....

 

There is no negative to have it connected to the battery at all of the time, but than it will be on the wrong side of the relay /wiring and wont be suefull.. Normally they are charged across a resistor to limit charging current ( I warned you about this on the FB). Once at full charge it works as it should.
To have it disconnected. Have a relay that connects the Capacitor to the battery at first across a resistor, and than connect completely once Voltage difference is small with another relay. I would advice to have the Cap as close to the ESC as possible. Wired directly and absolutely not across a relay. The currents are to great (not average but ripple current which is the whole point of the CAP.)

PS: What kind of battery do you use to have BMS built in ?

 

All very well to say "connect a resistor " but what size and what does the wiring layout look like between the relay and the ESC? My electrical knowledge on this is next to nil.

I made an LTO battery and bought a BMS and charger separately to go with it .... another one of those 'just do it' and x fingers it works deals. It worked .... the capacitor ............didn't.

 

I can provide you with all of the information. That is not a problem. Wiring diagram , components ect..
A very common way of charging a resistor is with a halogen light bulb. That way, you know exactly when it charged up as the light will go out. While its charging the Voltage difference is maximal thus it illuminates the most.
I will provide you with more detail later. Busy at work atm to sketch.

 

That would be awesome ...thanks. No hurry, I'll be on a road trip for the next week.

 

Back onto this.
Came back from my turbo test tour to find the starter battery flat on Bluey. Think this was due to the way I set up the charger.
So, today I changed the way the charger was working by adding a trigger wire to it. Worked wonders getting more charge current and fingers xd ...no flat battery now.

Next , I'll be fitting the capacitor and seeing if that does anything for top end . Have all the components and circuit diagram ready to go (thanks AAaF).

 

Got the capacitor working after some difficulty (some of it self induced). Thanks to Aaaf for all the help and advice.
After testing I can say it's definitely improved over not having the cap. but only marginally improved over the previous Lipo setup where the batteries were right next to the ESC.
Below log is second gear ...... in third it peaks at 250 showing battery degradation over time. The midrange is pretty epic though - everything I'd hoped for.


BMS shows a peak of 10.6 KW which is up from 10.1 without the cap.

Next step ... add some finese to the W/M control such that it only activates in boost.
Then : Aduino control of ESC for better driveability.

 

what is this software you use for power calculation

 

From the BMS : https://www.rx8club.com/series-i-maj...6/#post5002998

 

I meant the "virtual dyno" sorry.

 

Oh ...it's just what comes with Mazdaedit. Have used it for years and made comparisons with actual dynos of the same setup.

 

Warning, rabbit hole goes deep.

 

Not worth it ?

 

Depends. Ever wondered why oems seemingly have 100's of apparently useless maps ? Care to find out? Care to replicate all that on your own effort, trial and error, possibly blow up some things along the way?

 

More and more those are for emissions. And emissions tampering controll/detection...

 

Short answer ...no. I do have someone helping who is well acquainted with them and can write code though.

 

Found a way to charge batteries to 52V (bit mickey mouse but it works) and get a little more power up top.
Armed with that I went to a roll racing event today . System went great but the only race I won was when someone else messed up. Need another 50whp to get competitive but had a blast!
First race in actual competition was vs a 1000+hp Dodge charger. Decided to cheat a little and nailed it early so I at least got to be in front for a while while he struggled to get traction. Have videos but probably not worth posting all the losses.

 

First round of the eliminations. Big loss but was fun all the same
https://www.facebook.com/100009115006963/videos/1449519513165112/
Sitting at staging grid before the race.


Another loss but check out the commentary at the end.
https://www.facebook.com/100009115006963/videos/1264299305301295/