twin electric - one battery or two

[npowell28]

Ok guys. Should i use 2 x 11.1v 1800mah lipos or just one for my twin motor cargo plane?

Cheers

Neil

[coreman]

Originally Posted by npowell28

Ok guys. Should i use 2 x 11.1v 1800mah lipos or just one for my twin motor cargo plane?

Cheers

Neil

Some of it depends on the design. I use two on mine (see avatar) but that allowed me to put them in the fuselage pods which helped with the CG. You can certainly use one.

Be sure to remove the red wire from one of the ESC plugs so the Rx is only powered by one BEC

[r_kopka]

If you use two it is safer to connect them in parallel or you could have one ESC shut down before the other which is no fun.

RK

[rcers]

Originally Posted by r_kopka

If you use two it is safer to connect them in parallel or you could have one ESC shut down before the other which is no fun.

RK

+1 - use one or parallel or you run the risk of one motor completely quitting if you get to LVC.

Not a fun thing.

[npowell28]

i'm guessing then that if i use 1 it will still supply the same voltage to the 2 motors e.g. 11.1 volts each(appreciate that they will drop), but will not last as long as if each motor had thier own battery?

[solentlife]

The use of two in my book is good if you can accommodate them. It gives greater versatility in where place and CoG ... possibly greater capacity as well due to splitting the packs.
The only problem that may come up is the distance between to connect ... long leads to ESC's and all that .....

Nigel

[npowell28]

Originally Posted by solentlife

The use of two in my book is good if you can accommodate them. It gives greater versatility in where place and CoG ... possibly greater capacity as well due to splitting the packs.
The only problem that may come up is the distance between to connect ... long leads to ESC's and all that .....

Nigel

Esc's are no problem. i use wire from a kettle lead to lengthen them. will the battery still supply 11.1 volts to each motor or does it split the voths in half? My limited knowledge shows again.

[pmullen503]

Originally Posted by npowell28

Esc's are no problem. i use wire from a kettle lead to lengthen them. will the battery still supply 11.1 volts to each motor or does it split the voths in half? My limited knowledge shows again.

If everything is wired in parallel as it should be, the voltage will stay the same with one or two packs.

[solentlife]

The usual advice is to only lengthen ESC to motor leads ...

It is usually advised NOT to lengthen Battery to ESC leads.

So taking that ... imagine how long the leads to parellel the packs .........

(I know plenty of people do actually lengthen leads and get away with it .. ). I'm just pointing it out before others chip in with it ...

Nigel

[npowell28]

Originally Posted by pmullen503

If everything is wired in parallel as it should be, the voltage will stay the same with one or two packs.

Ok so what lead do i need to connect one battery to 2 esc's. I've looked on my favourite giantshark site and can't find them. They are just 2 x batterys to 1 x esc

[stevecooper]

Pix's wroth a 100 wordsbubsteve

[pmullen503]

Originally Posted by npowell28

Ok so what lead do i need to connect one battery to 2 esc's. I've looked on my favourite giantshark site and can't find them. They are just 2 x batterys to 1 x esc

I would solder both reds and both blacks into a single battery connector, either directly or through short leads. You could plug a single battery into that or use a 2 into 1 parallel battery cable if/when you use a pair of batteries.

If your ESCs already have connectors you'll either have to cut them off and resolder them both to a single connector or make up your own 2 esc to 1 battery connector. A quick look to my connector supplier also didn't show a 2 ESC to 1 battery connector ready made.

[solentlife]

Originally Posted by npowell28

Ok so what lead do i need to connect one battery to 2 esc's. I've looked on my favourite giantshark site and can't find them. They are just 2 x batterys to 1 x esc

Decent grade cable ... plugs and leads same as you use now and solder up a cable to fit exactly your needs ....

I never buy such a readymade cable ... I always make myself. If you use Deans / XT60 / AP's etc. - the standard plugs / sockets - you can buy bags of them from your favourite shop or ebay / Hobby King etc.

For ESC to motor extension wire ... where I need to keep neat and lie alongside / inside a fuselage .... I use solid copper heavy duty household cable ..... this has minimum voltage drop and is stiff to be fixed in place. Easy to solder up etc.

Nigel

[npowell28]

Ok ESC to motor leads have now been lenghtened using wiring from an iron. WOrks fine. I've run it up for 4 five minute sessions and it's fine. Doesn't heat up at all.

Created a lead to attach one lipo to the 2 ESC's and that works great also. Decided to just use the one lipo to start with to keep the weight down a little. I've tested it and a 1800 lipo will safely last 5 minutes on about 3/5 thorottle. One question though. I guess that because there are 2 motors/esc's that the ampage(is that the right word) is doubled. Is that how it works? I thought getting a plane to fly was a big enough learning curve, the electrics side of it is even steeper. I think i'm starting to understand it now though.

[hayofstacks]

Yes, your amprage will double.

I like my batteries to be about double rated peak amprage for my motor, and at minimum, countinously at peak motor output.

For instance, if you have two 25amp motors, you want a battery rated to atleast 50 amps, but I would prefer higher to keep it on the safe side for the battery.

If you run two batteries in parrelel, the votage stays the same, but amperage will double for the battery capacity.

[quorneng]

npowell28
Yes each motor draws its required current (amps) so if you have two motors the battery will have to supply twice the current.

How long any set up runs for depends on the battery capacity.
Bigger the battery the longer it will run for, BUT bigger batteries weigh more, which will require more power to fly so it will be drained a bit faster.
The 'best' battery size will always be a compromise between weight and duration.

[solentlife]

I will add this to above replies ...

2 x 25A motor reqt's will be MORE than 50A effectively ... because of internal resistance and also losses via connections etc. Add another 10% minimum to play safe.

It may seem better to have a single LiPo .... but lets look at a set-up with twin 25A motors.
You will need a good battery pack that can handle a 55A draw without puffing. That's a serious HEAVY pack. As you increase C rating the weight goes up dramatically.

BUT if you split to two smaller packs - lets compare.

sa you need a 5 minute run .....

Single LiPo : 55A for 5 mins = 4.6 Ah .... but we neeed to keep reserve in pack to prevent destroying it ... ~35% .... so 4.6 x 1.35 = 6.2 Ah .... or 6200mAh size in a high C rating of a decent level (I would go ~40C to ensure a cool battery)....

Using Hobby King LiPo's for quick data .... we have a pack of - couldn't find a 6000 pack of suitable C !!

Capacity: 5000mAh
Configuration: 3S1P / 11.1v / 3Cell
Constant Discharge: 40C
Peak Discharge (10sec): 50C
Pack Weight: 443g
Pack Size: 145 x 50 x 27mm

Now Split packs : 25A for 5 mins = 2.1 Ah .... so 2.1 x 1.35 = 2.8 Ah .. or a 2800 mAh size in a lesser C rating ... a 25C would be OK.

Minimum Capacity: 2200mAh
Configuration: 3S1P / 11.1v / 3Cell
Constant Discharge: 25C
Peak Discharge (10sec): 35C
Pack Weight: 188g .... giving a total of 376gr
Pack Size: 105 x 33 x 24mm


I kept both packs in relation to each other for comparison. I think I would be more inclined given the reduction in C rating needed for each pack ... greatly reduced weight, pricing of packs, to go the split pack route.

Just my thoughts .......

Nigel

[pmullen503]

+1 on what Nigel said. I've found twin packs cost less, are easier to cool and are easier to locate in the plane than a single pack of similar capacity.

[r_kopka]

Originally Posted by solentlife

sa you need a 5 minute run .....

Single LiPo : 55A for 5 mins = 4.6 Ah .... but we neeed to keep reserve in pack to prevent destroying it ... ~35% .... so 4.6 x 1.35 = 6.2 Ah .... or 6200mAh size in a high C rating of a decent level (I would go ~40C to ensure a cool battery)....

Using Hobby King LiPo's for quick data .... we have a pack of - couldn't find a 6000 pack of suitable C !!

Capacity: 5000mAh
Configuration: 3S1P / 11.1v / 3Cell
Constant Discharge: 40C
Peak Discharge (10sec): 50C
Pack Weight: 443g
Pack Size: 145 x 50 x 27mm

Now Split packs : 25A for 5 mins = 2.1 Ah .... so 2.1 x 1.35 = 2.8 Ah .. or a 2800 mAh size in a lesser C rating ... a 25C would be OK.

Minimum Capacity: 2200mAh
Configuration: 3S1P / 11.1v / 3Cell
Constant Discharge: 25C
Peak Discharge (10sec): 35C
Pack Weight: 188g .... giving a total of 376gr
Pack Size: 105 x 33 x 24mm

I kept both packs in relation to each other for comparison. I think I would be more inclined given the reduction in C rating needed for each pack ... greatly reduced weight, pricing of packs, to go the split pack route.

But the single pack has 12% more capacity and only 18% more weight. 3,6% difference pro double. But you also need more cabling. So more or less the same. On the other hand your single pack has 40/50C compared to 25/35C which will also lead to more weight.

The other point is: 5min are usually not at full throttle. Of course there are exceptions (pylon...) but usually you have more of a 50-70% average power level and short spikes are not much of a problem.

RK

[solentlife]

Originally Posted by r_kopka

But the single pack has 12% more capacity and only 18% more weight. 3,6% difference pro double. But you also need more cabling. So more or less the same. On the other hand your single pack has 40/50C compared to 25/35C which will also lead to more weight.

The other point is: 5min are usually not at full throttle. Of course there are exceptions (pylon...) but usually you have more of a 50-70% average power level and short spikes are not much of a problem.

RK

Maybe you missed the overall point ... with the two pack system - lower rated ESC's .. lower rated C packs ... easier to distribute weight for CoG ... lower prices .... and forgive me for saying - lower weight overall.

I not only do this for multi - but also for single motor set-ups where I need to be careful on weight and CoG .. such as the profile Me109 I have on the bench.

The factor of 5 mins is taken as WOT and worse case scenario - of course you will get longer with throtttling - but we need a benchmark to satisfy the calculation and WOT is the best as it's the worst possible. You then know you have time to go round again for landing etc. on timer.

Pls look at wider picture and note that I used the packs I could find quickly while writing the reply.

Nigel

[rcers]

The best reason to use two packs (I do it all the time) is so you can use the individual packs and smaller planes. So my twins all use two 1800-2200's that I can use two of then I can use one in the T-28 F4F, Four Star or Corsair.

Mike

[coreman]

Originally Posted by rcers

The best reason to use two packs (I do it all the time) is so you can use the individual packs and smaller planes. So my twins all use two 1800-2200's that I can use two of then I can use one in the T-28 F4F, Four Star or Corsair.

Mike

yep, my twin uses a pair of 1300s and my HK Artech Spitfire and Radian Pro use the same packs. That justifies buying more packs and not having to hassle with charging at the field

[solentlife]

Originally Posted by rcers

The best reason to use two packs (I do it all the time) is so you can use the individual packs and smaller planes. So my twins all use two 1800-2200's that I can use two of then I can use one in the T-28 F4F, Four Star or Corsair.

Mike

An excellent additional point.

I seem like most to be standardising on the 1800 - 2400mAh 3S packs ... so many models now can carry those and it's so much better to not have to think about different packs for different machines .. my 450 helis, Mig 3, EDF's, Cessna, Ultimate ... they all sit in that range ..

Nigel

[hayofstacks]

I would reccomend going with 2100's over 1800's. We ran two 1800's in my dads advanced instead of a single 3600. It worked well.

[r_kopka]

Originally Posted by solentlife

Maybe you missed the overall point ... with the two pack system - lower rated ESC's .. lower rated C packs ... easier to distribute weight for CoG ... lower prices .... and forgive me for saying - lower weight overall.

There seems to be some misunderstanding.

Weight distribution stays valid.

With a two pack system (independent of the number of motors but for each comparision the same number) you need exactly the same ESCs - the current will not lessen.

The C-rate must be the same if not more. A 2Ah pack with 10C gives you 20Amax. Two packs with 1Ah 10C give you 10A x 2 = 20Amax
But only if the cells are equal. If one is worse the current will be taken more from the better one. That brings a problem if the cells are also used standalone.

For an example I took two cells from the same label and the same shop:

LemonRC 2200/3s/35C - 173g €26,90
LemonRC 4500/3s/35C - 370g €45 -> half: 185g €22,5
so you gain 24g or 6% and loose 20% in cost with the two pack solution which has 2% less capacity.

Dymond 2400/3s/30C 202g 26,90
Dymond 5000/3s/30C 426g 46,90 -> half: 213g €23,45
so you gain 22g or 5% and loose 15% in cost with the two pack solution which has 4% less capacity.

Yes, the two pack solution is lighter but not cheaper. The gain is only some %.

The factor of 5 mins is taken as WOT and worse case scenario - of course you will get longer with throtttling - but we need a benchmark to satisfy the calculation and WOT is the best as it's the worst possible. You then know you have time to go round again for landing etc. on timer.

Pls look at wider picture and note that I used the packs I could find quickly while writing the reply.

I noted that but it will lead to different results if one compares unequal cells.

It also depends on what you intend. 5min WOT is a safe assumption. For a pylon or some other model that needs mostly WOT you get the correct result. But if the model is more like a trainer which runs most of the time at lets say 50% you get about 10min of flying time. That my be OK too but leads to too big batteries if only flown for 5min each time. A safe but heavy solution.

RK