LiPo batteries for air starts

I'd go with a 3 cell (12.6 volts fully charged) and rated for 10 amps continuous discharge (5 amps per starter). Maybe this one:

https://hobbyking.com/hobbyking/sto...00mah_3S_25_50C_Lipo_Pack_USA_Warehouse_.html

That charger will work just fine. You might also consider this one:

https://hobbyking.com/hobbyking/sto..._6_50W_6A_Balancer_Charger_w_Accessories.html

It has more capability for fast charging. I have one of these for my RC airplanes. I use it mostly for Tx and Rx batteries, but I also use it for my smaller electrics. Just make sure you order it from one of the US warehouses (currently out of stock). Shipping from Hong Kong is brutal.

Rob Campbell said:

That charger will work just fine. You might also consider this one:

https://hobbyking.com/hobbyking/sto..._6_50W_6A_Balancer_Charger_w_Accessories.html

It has more capability for fast charging. I have one of these for my RC airplanes. I use it mostly for Tx and Rx batteries, but I also use it for my smaller electrics. Just make sure you order it from one of the US warehouses (currently out of stock). Shipping from Hong Kong is brutal.

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That's the one I have and I like it a lot.
Just remember that it doesn't come with a power supply (go figure).

You can pick up a surplus computer or server power supply on evil bay pretty cheap.

Rob Campbell said:

You can pick up a surplus computer or server power supply on evil bay pretty cheap.

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I would just use a small SLA battery I have, or hook it up to my truck battery at the field.

Rob Campbell said:

That charger will work just fine. You might also consider this one:

https://hobbyking.com/hobbyking/sto..._6_50W_6A_Balancer_Charger_w_Accessories.html

It has more capability for fast charging. I have one of these for my RC airplanes. I use it mostly for Tx and Rx batteries, but I also use it for my smaller electrics. Just make sure you order it from one of the US warehouses (currently out of stock). Shipping from Hong Kong is brutal.

Click to expand...

That's the one I have, too. At home, I use a bench supply converted PC power supply to power it.

I bought this one:
https://hobbyking.com/hobbyking/store/__6478__IMAX_B6_AC_Charger_Discharger_1_6_Cells_GENUINE_.html

It can do AC or DC just plug it in and charge away.

JD

JDcluster said:

I bought this one:
https://hobbyking.com/hobbyking/store/__6478__IMAX_B6_AC_Charger_Discharger_1_6_Cells_GENUINE_.html

It can do AC or DC just plug it in and charge away.

JD

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Price is right and the charger will work on the bench at home or on 12V at the range.

I'm assuming that you recommend this because it's worked for you?

It was recommended by another user here on TRF.
I was buying needed parts for my Eggfinder TRS system and needed some lipo batteries.
I'm not an RC guy and had no idea on what to buy.

It has already saved one battery from death after a rookie mistake using Lipo batteries.


JD

o1d_dude said:

Price is right and the charger will work on the bench at home or on 12V at the range.

I'm assuming that you recommend this because it's worked for you?

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The one thing that I was a little disappointed with was: that
the lack of different connector ends.

I placed a second order about 3 weeks later
for a multi end connector:

https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=55432

It makes it much easier than having to dig around for the correct connector.


JD

qquake2k said:

I've been working on a project for a while that will have two CTI air started H motors. I already have the Missileworks PET2+ timer. Since it will be lighting two motors, I'd like to use something with more capacity than an alkaline 9 volt. I'm thinking a LiPo battery would be my best bet. Has anyone used a LiPo to light two or more motors? Any recommendations?

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Becareful of the igniter duty cycle setting on your altimeter. Triggering such high currents through a standard altimeter for more than a few hundred milliseconds will most likely burn up your altimeter.


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Random Flying Object said:

Becareful of the igniter duty cycle setting on your altimeter. Triggering such high currents through a standard altimeter for more than a few hundred milliseconds will most likely burn up your altimeter.


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I'll be using the PET2+ timer from Missile Works. It's rated at 5A @ 0.5sec. I'll be using CTI igniters for the air starts.

https://www.missileworks.com/store/#!/PET2+-Programmable-Event-Timer/p/24591235/category=5760486

qquake2k said:

I'll be using the PET2+ timer from Missile Works. It's rated at 5A @ 0.5sec. I'll be using CTI igniters for the air starts.

https://www.missileworks.com/store/#!/PET2+-Programmable-Event-Timer/p/24591235/category=5760486

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If you are using a LiPo the current will most likely be significantly higher.

I messed up and forgot about a setting I was using for ground testing. During a flight the drogue came out and the AV bay proceeded to catch on fire. I forgot to set the duty cycle back down to 50ms. I had a 3S LiPo pack on the altimeter. In this case the current was up around 30A for about 2s. Needless to say there wasn't much left in the AV bay by the time it hit the ground.

All of this is what lead me to design and build a circuit specifically for igniting motors from altimeters, basically a small solid state relay with continuity check.



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Adrian Adamson of Featherweight has mentioned this a number of times with regards to airstarts. The problem is that the plasma in the motor during ignition results in effectively a dead short until the igniter is ejected. At that point, current is limited only by the internal resistance of the battery, which is pretty low in the case of LiPo batteries. The result is a very high current for the duration of the on cycle. That is why he recommends single-cell LiPos for the Raven.

David

qquake2k said:

I've been working on a project for a while that will have two CTI air started H motors. I already have the Missileworks PET2+ timer. Since it will be lighting two motors, I'd like to use something with more capacity than an alkaline 9 volt. I'm thinking a LiPo battery would be my best bet. Has anyone used a LiPo to light two or more motors? Any recommendations?

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If you are using CTI motors with their ematch igniter and the powder pelts in the motors, a 9 volt should be great plenty. They fire multiple ematches for dual deploy all the time.

My biggest worry would be making sure the igniter stayed close enough to the pelt during the booster burn.

Handeman said:

My biggest worry would be making sure the igniter stayed close enough to the pelt during the booster burn.

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Legitimate concern; I have even bent horizontally oriented TO-220s under heavy boost.

Handeman said:

If you are using CTI motors with their ematch igniter and the powder pelts in the motors, a 9 volt should be great plenty. They fire multiple ematches for dual deploy all the time.

My biggest worry would be making sure the igniter stayed close enough to the pelt during the booster burn.

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I agree. I've done 5 Q2's off of one 9V in my older PET2. Prior to that specific flight I had several exchanges with Jim Amos about higher current options and discussed the 2 9V "high current" schematic. He really recommended against using it, saying a single 9V would be very sufficient for my needs...and it worked! IIRC he said (or I read somewhere) that a single 9V could be good for up to 6 e-matches.


I'm definitely in the woods when it comes to LiPos and R/C stuff as it seems you have to take some extra precaution with them...something I'd probably mess up! Better safe than sorry though!

qquake2k said:

I emailed Missile Works today. Here is what I said:

Hello. I purchased a PET2+ timer a while back, that I plan on using for air starting two CTI H motors. I'll be using a 1000MAH 3S 25C LiPo battery. This battery is capable of delivering 25A continuous, and a 35A burst. Will there be any problems using this battery with the PET2+? Could it conceivably "fry" the timer?


And Jim Amos' answer:

"Conceivably", yes... Provided you use low current ignition devices, it "should" be OK. There's much more potential to draw excess current in motor ignition due to metalized ignition by-products.

While heavier, a 9V alkaline is naturally current limited to the current sink rating of the PET2+ outputs and would ensure there's the lowest potential for damage to the output FET's. It should also have more than enough capacity for a dual ematch air start.

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AH! You posted that while I was between typing the above post and working. A lot of what he mentioned above is very similar to what he told me. You just don't need all that battery...it's designed for 9Vs.

watermelonman said:

Legitimate concern; I have even bent horizontally oriented TO-220s under heavy boost.

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Indeed. A really thin dowel taped to the match will help. This technique is really recommended for larger motors, but a really thin dowel will help it be more rigid. Just make sure it has an escape route and can't get caught up in the motor!

qquake2k said:

I'm not sure I understand how a LiPo would make the current higher. Just because it has the capacity, it still won't flow more current than is drawn by the igniters.

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The internal resistance of a LiPo is significantly lower than many other battery chemistry's.

In a shorting or very close to shorting circuit the internal resistance of your source plays a large part in limiting current.


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Random Flying Object said:

The internal resistance of a LiPo is significantly lower than many other battery chemistry's.

In a shorting or very close to shorting circuit the internal resistance of your source plays a large part in limiting current.


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Click to expand...

Exactly.

Try this link:
https://www.rchelicopterfun.com/rc-lipo-batteries.html

JD

I have a PET2 and I will be using a 9v. I have used other timers and altimeters for countless staging and airstarting events, all w 9volt new Duracel alkiline batteries. Good luck!