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EMAC - Electric ONLY IMAC Events

Discussion in 'IMAC>>>Aircraft, Techniques, Equipment, etc.' started by Fliprob17, Aug 21, 2012.

  1. Aeroplayin

    Aeroplayin 70cc twin V2

    I see where you're going with this and I have to think about it again because I did try something like this when we went to the Venice Huckfest with no luck. They did have outlets so it all worked out, but the portable battery thing was a disappointment.

    I will add that the 12v battery is virtually dead at 12v, just like a Lipo cell is virtually spent at 3.7v, so it should meter upwards of 15v when fully charged. So although it has the capacity to recharge eight 5000mAh batteries, I'm pretty sure one of these does not have the voltage requirements to recharge a 6S Lipo. Now two in series will give you the same capacity with twice the voltage, and this may be the way to go, but I'm not sure (yet).
  2. Bigroger

    Bigroger 70cc twin V2

    I haven't got any 6s5000 packs yet, but 5 40C 6s3300 packs I can test this out on.

    I know I could charge at 20A 4x6s3300 packs in parallel the other day in the shed for a test, but I didn't charge to completion as yet to test.

    I'll do a trial run today in the shed and fill up the 4 x 6s3300 packs in parallel and see how long it takes and so forth.

    The actual 12V from the deep cycle battery isn't an issue as the iCharger converts that up to the required lipo voltage, just uses more mA to do the upstep and I assume consumes more Amps out of the deep cycle in the process.

    It becomes a bit of a mute point and possible need for a decent generator/ extra batteries play off.

    A good honda 2kV generator will set me back about $1600 and for that value I could buy a lot of 6s5000 packs.
  3. Aeroplayin

    Aeroplayin 70cc twin V2

    That has always been my thinking too. I can bring a lot of batteries to the field regardless if electric is available. I can also buy a small 800 Watt portable generator for between $100 and $180. Even on the 35% Laser, if I was going through two IMAC flights per day, with two full sequences per flight, I can do it on a 4-pack per flight, which means eight batteries per day since you really can't fun-fly during an event. On a practice day at our field, which has 48 outlets and four double hangars, I can charge my batteries as easy as if I were at home. I can buy twelve 6S Sky's for under $1000, so I don't see it as a problem. The problem is only to make sure I can get two full sequences, all the way to Unlimited, completed in 9.5 to 10 minutes.

    So far, the guys I know that have timed their Unlimited sequences, tell me that I need 9.5 minutes from wheels-off to wheels-on.
  4. Bigroger

    Bigroger 70cc twin V2

    I don't see that as a problem.
    James told me his 88" edge on the Q80-8 with 24x10TH prop, with good 65C 6s5000 packs can get 7-8 minutes of medium 3D flying.

    Drops down to 5-5.30 minutes when he throws in lots of high energy stuff, tumbles, riffle rollers, etc.

    IMAC patterns, I just don't know how much mA will be consumed, sure the uplines are gonna pull some electrons out, but the down lines can be low throttle.

    Guess the only way is to get Tom to fly some sequences in the 10S Godfrey and see how many mA he consumes for the higher level sequences.

    By the way, I charged 4 6s3300 packs last night off the deep cycle battery at 20A. Any more amps and the iCharger started hunting around trying to keep the charge.

    So 4 x 6s3300 from 3.85V per cell to fully charged took about 30 minutes, and put in about 6660mA total.

    Don't know how much it took out of the deep cycle battery to get to that level, but my 1.6A trickle charger topped the deep cycle back up within 6 hours no problem.
  5. 3dNater

    3dNater 3DRCF Regional Ambassador

    I'd guess you used about 13 amp hours out of your deep cycle.

  6. Bigroger

    Bigroger 70cc twin V2

    Probably, based on 1.6A charge over 6 hours = 9.6A to refill the deep cycle battery.
  7. 3dNater

    3dNater 3DRCF Regional Ambassador

    So a rule of thumb is take your cell count/3 and multiply it by the number of amp hours you have taken out and you should be pretty safe. So say you put 3000 mah back into a 5s pack. 5/3=1.66 * 3= 5 amp hours out of the deep cycle. It won't be perfect but from the sound of things it is a conservative estimate and will keep your deep cycle battery safe from over-discharging.

    Now say you are charging an 8s pack and put 3000 mah back in. (8/3)*3= 8 amp hours.

    2s pack putting 3000 mah back in. (2/3) * 3= 2 amp hours.

    Basically you are trying to convert the mah from the different cell counts into mah at 12v to estimate how much power has been taken from the deep cycle battery. The whole basis is that a 3s lipo is close to the same voltage as the deep cycle. Since it is less (11.1) you are erring on the safe side.
    Last edited by a moderator: Aug 30, 2012
  8. Bigroger

    Bigroger 70cc twin V2

    I spoke with my deep cycle battery supplier today about how many mA out of my 87Ah battery I can extract without harming the battery,

    rule of thumb given was 75-80% is safe as long as you put the battery back on the charger the same day without letting it sit in the discharged state.
    based on that I should get 500-600 cycles easy out of the deep cycle battery.
  9. 3dNater

    3dNater 3DRCF Regional Ambassador

    sweet so you should be able to charge quite a few packs then.
  10. Aeroplayin

    Aeroplayin 70cc twin V2

    Sorry, it's been a while since I stopped by. Been busy...

    Tom has already put the 300 through it's paces on a few IMAC basic sequences and he went from an average of 740.88mAh/min to 860.89mAh/min. So big sky IMAC will consume battery capacity at a rate of 16% more than his 3D style. So in relative time, a 5.5 minute flight becomes a 4.4 minute flight (4 mins and 24 seconds).

    That also means that my 4-pack in the 24 pound, 101 inch Godfrey Laser 200 will have to carry:

    860.89 x 9.5 mins = 8179mAh x 1.25 = 10.22Ah to complete 9.5 minutes and use only 75% of the full capacity. So four Gens 6S 5500mAh should do it in theory, and my weight differential in my power app says that the 143 peak Amps I'll get from that setup means 11Ah will give me 10.7 minutes. The calculations are right on the money for all the other planes I've every compared with it, so now there is one thing left to do.
    Last edited by a moderator: Sep 12, 2012

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