Twin motors, twin batteries, twin problems - Page 2

Ira NZ · Nov 05, 2009, 03:38 AM

There you go, I didn't have any way of drawing something like that here at work. My suggestion is just basically shortening the wires between the two soldered connections to zero.

noblapod · Nov 05, 2009, 02:47 PM

Most people (myself included) use 1 battery pack for each motor and do not parallel them together. The reason I was told not to parallel the packs is due to problems if you hit lvc. One esc will hit lvc first and when the load of one motor is removed from the system the voltage will then rise on the other motor causing it to speed up which is the opposite to what is needed! I fly my Dual Ace on 5350's and the motors run within 150 rpm of each other. I am not sure of any benefits to be gained by paralleling the packs. Probably others have different ideas though.
Chris....UK

ggcrandall1 · Nov 05, 2009, 04:25 PM

Noblapod,

You should not be flying to LVC. Land before you reach that point and the parallel battery question is moot.

Glen

Ira NZ · Nov 06, 2009, 02:19 AM

Like Glen said, you shouldn't be flying to LVC anyway. Paralleling them ensures that both motors get the same voltage. Otherwise a slightly weaker or stronger battery will cause a thrust differential.

Of course, then you still have possible differences from the esc and motors, but at least you've cut out one cause.

noblapod · Nov 07, 2009, 12:24 PM

I totally agree about not discharging to lvc. I always try to keep to 80% maximum discharge. It is possible to get caught out at times. Very windy weather can cut flight times and catch you out though. There are many twin engine electric models in which the battery packs are fitted in the nacelles and they are most certainly NOT paralled together. I have never had a problem with having seperate battery packs and would not bother to parallel them. Paralleling packs can have problems of it's own as both packs need to be identical and have the same number of charge/discharge cycles on them otherwise there can be safety implications, especially with lipos. However you decide to arrange your setup, enjoy your model. Twins are fun!
All the best...Chris UK.

abenn · Nov 07, 2009, 02:12 PM

So long as the packs are the same voltage (i.e. same cell-count, same chemistry, and same state of charge), paralleling them has no safety implications that I can think of, so long as one is sensible to be aware of the pitfalls.

Note, I didn't mention same capacity, though the ideal setup will use two identical packs: So long as voltages are the same when connected, it doesn't matter if the packs are different mAh, they'll keep the same voltage as each other for so long as they're connected. This leads to the one potential pitfall that I can think of -- if the packs are different mAh, the higher mAh pack will provide more of the amps than the lower mAh pack (to keep the voltages the same at all times), so you need to be sure that it's big enough and/or high enough C rating.

The advantage of paralleling is that you can be sure both ESC/motors are getting the exact same voltage and, therefore, will be spinning as near as possible at the same rpm. Also, not all models have nacelles large enough to accomodate separate batteries; and/or c of g considerations may require the batteries to be further forward than can be achieved in the nacelles. The practical disadvantage is lead length, but this can be remedied by the addition of appropriate capacitors.

Zagabond · Nov 07, 2009, 05:24 PM

I had a similar set up in my Dual Ace twin, I was using a 5s2p A123 pack (two packs in parallel). My wiring was getting hot. Too hot to be comfortable, so I split it up into two 5s1p packs, one pack for each motor and speed control. I have not had any issues with one motor running longer than the other, in fact, they have been nearly dead equal in run time since I put this together. I probably have about 20 flights on the plane at this time.

I wouldnt be afraid to use the 5s1p packs, especially if you are timing your flights and being a little bit conservative. You should be timing them anyway, since you likely have a fair investment in that model and I am sure you dont want to lose it due to battery run-down and subsequent dead stick.

I have landed my Dual Ace completely dead stick a few times, now I am much more careful. I time the flights and land a little early. I want to be on the field and not in the weeds (or worse) and still have enough power to taxi back to me.

One more thing, its easier to run a separate pack for each motor... It was a win-win situation for my application.

lyclyc · Nov 08, 2009, 07:15 AM

i still think that the twin motors that are not spinning at the same speed will only add more fun for you to control the rudder?

this will train the flying skill more?

Nov 07, 2009, 05:24 PM	#23
Zagabond Registered User Join Date: Mar 2004 Location: Central Pennsylvania Posts: 366	hot wires I had a similar set up in my Dual Ace twin, I was using a 5s2p A123 pack (two packs in parallel). My wiring was getting hot. Too hot to be comfortable, so I split it up into two 5s1p packs, one pack for each motor and speed control. I have not had any issues with one motor running longer than the other, in fact, they have been nearly dead equal in run time since I put this together. I probably have about 20 flights on the plane at this time. I wouldnt be afraid to use the 5s1p packs, especially if you are timing your flights and being a little bit conservative. You should be timing them anyway, since you likely have a fair investment in that model and I am sure you dont want to lose it due to battery run-down and subsequent dead stick. I have landed my Dual Ace completely dead stick a few times, now I am much more careful. I time the flights and land a little early. I want to be on the field and not in the weeds (or worse) and still have enough power to taxi back to me. One more thing, its easier to run a separate pack for each motor... It was a win-win situation for my application.

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Nov 05, 2009, 03:38 AM	#16
Ira NZ Bombs away! Err...landing Join Date: Apr 2006 Location: Upper Hutt, New Zealand Posts: 1,542	There you go, I didn't have any way of drawing something like that here at work. My suggestion is just basically shortening the wires between the two soldered connections to zero.

Nov 05, 2009, 02:47 PM	#17
noblapod Registered User Join Date: May 2005 Location: Rural NW Essex,England. Posts: 192	Most people (myself included) use 1 battery pack for each motor and do not parallel them together. The reason I was told not to parallel the packs is due to problems if you hit lvc. One esc will hit lvc first and when the load of one motor is removed from the system the voltage will then rise on the other motor causing it to speed up which is the opposite to what is needed! I fly my Dual Ace on 5350's and the motors run within 150 rpm of each other. I am not sure of any benefits to be gained by paralleling the packs. Probably others have different ideas though. Chris....UK

Nov 05, 2009, 04:25 PM	#18
ggcrandall1 Registered User Join Date: Aug 2005 Location: Marietta, GA Posts: 1,073	Noblapod, You should not be flying to LVC. Land before you reach that point and the parallel battery question is moot. Glen

Nov 06, 2009, 02:19 AM	#20
Ira NZ Bombs away! Err...landing Join Date: Apr 2006 Location: Upper Hutt, New Zealand Posts: 1,542	Like Glen said, you shouldn't be flying to LVC anyway. Paralleling them ensures that both motors get the same voltage. Otherwise a slightly weaker or stronger battery will cause a thrust differential. Of course, then you still have possible differences from the esc and motors, but at least you've cut out one cause.

Nov 07, 2009, 12:24 PM	#21
noblapod Registered User Join Date: May 2005 Location: Rural NW Essex,England. Posts: 192	I totally agree about not discharging to lvc. I always try to keep to 80% maximum discharge. It is possible to get caught out at times. Very windy weather can cut flight times and catch you out though. There are many twin engine electric models in which the battery packs are fitted in the nacelles and they are most certainly NOT paralled together. I have never had a problem with having seperate battery packs and would not bother to parallel them. Paralleling packs can have problems of it's own as both packs need to be identical and have the same number of charge/discharge cycles on them otherwise there can be safety implications, especially with lipos. However you decide to arrange your setup, enjoy your model. Twins are fun! All the best...Chris UK.

Nov 07, 2009, 02:12 PM	#22
abenn Registered User Join Date: Jul 2004 Location: Letchworth, Great Britain (UK) Posts: 5,683	So long as the packs are the same voltage (i.e. same cell-count, same chemistry, and same state of charge), paralleling them has no safety implications that I can think of, so long as one is sensible to be aware of the pitfalls. Note, I didn't mention same capacity, though the ideal setup will use two identical packs: So long as voltages are the same when connected, it doesn't matter if the packs are different mAh, they'll keep the same voltage as each other for so long as they're connected. This leads to the one potential pitfall that I can think of -- if the packs are different mAh, the higher mAh pack will provide more of the amps than the lower mAh pack (to keep the voltages the same at all times), so you need to be sure that it's big enough and/or high enough C rating. The advantage of paralleling is that you can be sure both ESC/motors are getting the exact same voltage and, therefore, will be spinning as near as possible at the same rpm. Also, not all models have nacelles large enough to accomodate separate batteries; and/or c of g considerations may require the batteries to be further forward than can be achieved in the nacelles. The practical disadvantage is lead length, but this can be remedied by the addition of appropriate capacitors.

Nov 08, 2009, 07:15 AM	#24
lyclyc Pirouetting flip master Join Date: Jul 2007 Location: Malaysia Posts: 612	i still think that the twin motors that are not spinning at the same speed will only add more fun for you to control the rudder? this will train the flying skill more?