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Dec 30, 2011, 01:57 PM
Dale Kramer
KiloOne's Avatar
Quote:
Originally Posted by g00bd0g
One thing you really want to pay attention to is quiescent current draw of your BMS systems. Make sure it is very low or can be completely disconnect from the cells, or else you may end up with a Battery Murdering System. Even months of "stand-by" is not enough, people cannot be trusted to keep their systems topped up and maintained. Somebody will run their pack flat, stick it in the hangar for a year and then get pissed when it doesn't work anymore...
Excellent point, I was looking at the LVC/HVC components that user 'methods' (endless-sphere.com) chose for his project. I think he ended up with 6ua draw in monitor mode and about 200ua in LV mode. So, I've been thinking about this and I decided that was still too much as you suggest above. When you are not flying or charging, any draw is likely too much, especially if someone leaves the battery discharged at LVC voltage.

So, I decided that disconnecting the cells from even the LVC/HVC circuitry is a good idea.

Here is v1.2 of the functional schematic.

Note: I have not shown some detailed circuitry for a couple items, just a magic square (ie the 555 timer one shot component), to be filled in later at the detail design stage. In the same vein, I know that there likely is not a 9PST relay available, I could use a few DPDT's or 4PDT's (these contacts only need to handle the balancing current which is 1 amp for the PL8).

Dale
Last edited by KiloOne; Dec 30, 2011 at 03:20 PM.
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Dec 30, 2011, 02:15 PM
Registered User
Thanks for taking the time to reply Dale, The BVS8s looks very interesting, a 'better' cellog8 sounds worth looking into. Your battery system has been extremely interesting to me for my landspeed record project (which will have 4x 20kg battery packs; obviously my requirements are completely different to yours, but I did plan on recyling the batteries in a plane after finishing with the car ;^) Your failure statistics are gold dust.....
It's a completely different thing making something for sale & I can see you need to take as much risk out as possible, particularly if the system proves popular!
Sorry I misunderstood yr drawing, I had assumed that the battery 'blocks' must have some internal contactor to do with the "LVC/LHC latching" - so I guess that's just signal level stuff. The main issue I have with dry contacts in high current applications is when they weld closed, can happen due to contact resistance even if they are always actually switched with zero load.
Finally.... do you really need to reverse the motors? don't you get more braking by regenerating with the motors still going forwards? (sorry I'm fairly ignorant on these matters)
Happy new year everyone
Dec 30, 2011, 04:04 PM
Registered User
Quote:
Originally Posted by KiloOne
So in that vein, I have decided to seek 20 ampHr Li[NiCoMn]O2 cells made by EIG.
Any particular reason for going with the EIG cells?

A123 has 20 Ah cells available now, might be easier to get your hands on them.

http://www.a123systems.com/products-...pouch-cell.htm
Dec 30, 2011, 04:15 PM
Dale Kramer
KiloOne's Avatar
Quote:
Originally Posted by Helno
Any particular reason for going with the EIG cells?

A123 has 20 Ah cells available now, might be easier to get your hands on them.

http://www.a123systems.com/products-...pouch-cell.htm
Last time I checked, A123 cells would be over 30% heavier for the same energy.

Anyone know the weight of these cells or the whr/kg?

The EIG cells come in at 175 whr/kg

Dale
Dec 30, 2011, 04:44 PM
Dale Kramer
KiloOne's Avatar
Quote:
Originally Posted by bobc0
The main issue I have with dry contacts in high current applications is when they weld closed, can happen due to contact resistance even if they are always actually switched with zero load.
Here is the GX21 relay datasheet:
http://www.gigavac.com/products/cont...gx21/index.htm
I would assume that welding of contacts occurs at currents that are much higher than rated current and that if a fet was treated similarly the most likely outcome is an open circuit. I would then prefer the relay failure mode.

Quote:
Originally Posted by bobc0
Finally.... do you really need to reverse the motors? don't you get more braking by regenerating with the motors still going forwards?
Since our props are optimized for positive thrust, regenerative braking will not be very effective. I have not tested the negative thrust that I can obtain but I guess that I would get at least 1/2 the thrust I get positively which would provide very good glide path control and allow steep descents to be able to land in a smaller space.
Last edited by KiloOne; Dec 30, 2011 at 07:52 PM.
Dec 31, 2011, 10:03 AM
Registered User
There is a post on ES re: an EIG pack.

http://endless-sphere.com/forums/vie...&hilit=battery
Dec 31, 2011, 04:55 PM
Registered User
Quote:
Originally Posted by KiloOne
Last time I checked, A123 cells would be over 30% heavier for the same energy.

Anyone know the weight of these cells or the whr/kg?

The EIG cells come in at 175 whr/kg

Dale
They come in at 131 whr/kg and each cell weighs 496g.

The higher weight is a penatly but they are rated for substantially longer cycle life. 3000 cycles at 1c Charge 2C discharge before you hit 90% of rated.

Discharge curve is suposed to be flat as a pancake as well. I bet there are a few guys in the battery part of this forum that could tell you how well the M1 cells are holding up after all these years.
Dec 31, 2011, 06:17 PM
Dale Kramer
KiloOne's Avatar
Quote:
Originally Posted by Helno
They come in at 131 whr/kg and each cell weighs 496g.
Maybe the lighter pilots building their own conversion would be happy with an extra 30 lbs on the aircraft but for my weight and for a commercial product I prefer the EIG cells.

Dale
Jan 01, 2012, 08:11 PM
Registered User
Quote:
Originally Posted by KiloOne
extra 30 lbs on the aircraft
I keep forgetting that you are already at the weight limit for Far 103 operation.

Have yu contacted EIG directly? Seems like alot of suitable batteries are out there but good luck ever getting your hands on them.
Jan 03, 2012, 01:25 PM
Dale Kramer
KiloOne's Avatar
Quote:
Originally Posted by bobc0
I'd be tempted to use big MOSFETs instead with something like the FIA switch of a car....
Turns out that the GX21SAB contactor comes in at about $90 in quantity. This is more than I wanted to pay so I re-investigated a MOSFET/FIA solution for the high current contact and they looked to be about 1/4 that price, but it turns out that there is too much Vds leakage current for this application (if used without an FIA switch). The IRF1324PbF that I was looking at had 20ua leakage (and I needed 4 in parallel to bring the on contact resistance down to the 0.3 mohm of the GX21). I really need the 0ua drain (when open) of the GX21 solenoid contactor to keep the batteries from discharging when left months at a time.

Sure you get 0ua if you remember to turn off the FIA switch when you are done flying, but my timed safety circuit using a GX21 makes sure that the battery will ALWAYS (as long as the timer trips and the solenoid releases) be left in a 0 amp discharge mode even if you leave the ignition key on and walk away (and it does this for charging neglection too)

So, I bit the bullet and ordered two GX21SAB's at $129 each.

Dale
Last edited by KiloOne; Jan 03, 2012 at 04:41 PM.
Jan 03, 2012, 05:06 PM
Registered User
The contactor specs look pretty good & I can see the reasoning - leakage in a FET switch was always going to be 10s of uA. There's the size and weight to consider too - but at least it's a sealed design so the contacts should stay clean. I need a shed load of high current changeover relays for my car design & the only remotely suitable ones I could find were from kelly (they make controllers) and they didn't respond to questions..... :^(
One of the nice things about lithium batts is the low self discharge so I 'get' the zero draw point.
Actually the ones kelly sell may well be a subset of the albright (international) range
Last edited by bobc0; Jan 03, 2012 at 05:23 PM. Reason: point to albright too
Jan 11, 2012, 10:26 PM
Registered User

Kokam batteries


Sorry if this was covered by others, but could Dow Kokam be a source for LiPo batteries for this use? I think Electravia is using them in their MC30.
Jan 18, 2012, 11:09 AM
Dale Kramer
KiloOne's Avatar
Quote:
Originally Posted by Jboatri
... but could Dow Kokam be a source for LiPo batteries for this use? ...
I believe that the Kokam batteries are lithium cobalt chemistry and I have decided that this chemistry is too 'unstable' for my liking.

Dale
Jan 18, 2012, 01:15 PM
Dale Kramer
KiloOne's Avatar

2012 Update #1


Well, after another trip across the country and back in my RV8 to visit JOBY and others in the San Francisco area, I have convinced myself that I will have a continuing supply of EIG cells and motors at a reasonable cost.

Now on to the next order of business and that is to finance the startup of this new venture.

I have done enough costing analysis to determine that the target price of a complete eLazair kit (less batteries) will be about $20,000 and a fully assembled eLazair will be about $25,000 plus batteries.

Battery pricing will be $5-6,000 for packs with about 1 hour of flight endurance and with at least 1,000 flight hours of cycle life.

So, if you want to own a new eLazair with a coveted low serial number (serial #E0001 and up are now available), you can send a deposit of $5,000 to be held in escrow until your eLazair ships.

And/0r, if you would be interested in investing money in this new venture we can talk about that too.

Either way, just Private Message me or contact me at kci at vaxxine dot com.

Dale Kramer
Last edited by KiloOne; Jan 18, 2012 at 10:23 PM.
Jan 18, 2012, 01:40 PM
Call me Frosty
TheRealFrosty's Avatar
Have you examined http://www.kickstarter.com for fund raising? It seems to be very effective for some types of projects these days. Not sure how a project likes yours would fare on kickstarter since your potential customer base is different/smaller than the masses.


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