# Battery selection advice for custom launch box.

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#### ThirtyWest

##### New Member
Hi folks, first post. Be patient.

I'm working on a custom launch box / supply box combo. Just a few switches (and their respective lights) on the top: System power, safety momentary pushbutton, and launch pushbutton.

I won't be doing more than maybe 4 or 5 launches at a time and wondered if 12 volts would be enough--a couple of lantern batteries in series.

The issue I'm having is finding the current draw of ignitors. It seems like a tough number to zero in on for A or B engines.

I've got some nichrome wire on order and was going to kill two birds by making my own ignitors as well as measuring the amps when firing.

Just looking for some suggestions whilst I dig through the archives here.

Oh, and lamps versus LEDs on the launch controller. There's a bit more wiring involved putting LEDs in the mix but they are much friendlier on the current used.

#### MikeyDSlagle

##### Well-Known Member
Are you trying to launch 4 or 5 at a time?
HPR or LPR?
For my LPR I use 4 "C" batteries

#### ThirtyWest

##### New Member
Are you trying to launch 4 or 5 at a time?
HPR or LPR?
For my LPR I use 4 "C" batteries
Oh, right, sorry.

One, maybe two, at a time.

LPR definitely for now with MPR on the horizon soon.

I might add in there a few components to put up a red or green once the safety switch is depressed to indicate I've got sufficient voltage to get the job done. My bench power supply arrived in the mail too! That's for some other things as well, but always nice to see Amazon's box ACTUALLY have something inside for me and not just my name on the box.

#### MikeyDSlagle

##### Well-Known Member
Like I mentioned the one I built for home use uses 4 C cells internally. It also has some posts to hook and external battery and a switch to select between internal (6 volt via the 4 C cells) or the external battery which can be anything you want. The internal has pushed first fire juniors no problem. Been using the same batteries for over a year but just a few launches and ground tests.

I wouldn't recommend lantern batteries, mainly because of cost, size, availability. They'll work fine but a good rechargeable 12 volt battery would be more convenient. Maybe even a good R/C type battery pack.

Small 12 volt that will work
https://www.batteryplex.com/toyo.cfm/m/6FM4

Or a 6 volt.
https://www.batteryplex.com/lithoni...MI5aKCmsje1QIVzYqzCh00vQJXEAQYBCABEgIosPD_BwE

I use LEDs and the appropriate resistor. I have an LED for main power to tell which source I have it set to, and another for continuity, which is the only one necessary. I use an ATV key as the removable interlock. Think I paid 7 bucks for it on Amazon.

If you need a diagram or anything just let me know.

#### ThirtyWest

##### New Member
Like I mentioned the one I built for home use uses 4 C cells internally. It also has some posts to hook and external battery and a switch to select between internal (6 volt via the 4 C cells) or the external battery which can be anything you want. The internal has pushed first fire juniors no problem. Been using the same batteries for over a year but just a few launches and ground tests.

I wouldn't recommend lantern batteries, mainly because of cost, size, availability. They'll work fine but a good rechargeable 12 volt battery would be more convenient. Maybe even a good R/C type battery pack.

Small 12 volt that will work
https://www.batteryplex.com/toyo.cfm/m/6FM4

Or a 6 volt.
https://www.batteryplex.com/lithoni...MI5aKCmsje1QIVzYqzCh00vQJXEAQYBCABEgIosPD_BwE

I use LEDs and the appropriate resistor. I have an LED for main power to tell which source I have it set to, and another for continuity, which is the only one necessary. I use an ATV key as the removable interlock. Think I paid 7 bucks for it on Amazon.

If you need a diagram or anything just let me know.

yeah, i'd like to see how you set things up.

#### MikeyDSlagle

##### Well-Known Member
I'll get something drawn up for ya. I got a stupid schedule at work so it may take a bit but I'll get it.

#### MikeyDSlagle

##### Well-Known Member
I had a bit fo time today so I opened up my controller box and picked through my wires. I reverse engineered my own design by digging through the rat nest of wires, I ended up with this.

For the resistor values. I try to get 12 to 15 Ma to the LEDs. So using that and Ohm's law:

External battery is 12 volts: R2 and R3 will be 800 to 1000 ohm. The continuity LED will be a bit dimmer but it would take a bit more wiring to get two separate resistors from the two separate power sources on the continuity circuit. And it just wasn't worth it to me.

Internal battery is 6 volts: R1 will need to be 400 to 500 ohm.

Internal battery is 7.2 volts: R1 will need to be 480 through 600 ohm.

A 500 will most likely work with either the 4 C batteries at 6 volts or a rechargeable NiCad pack at 7.2 volts. I actually use 500 ohm for R1 and R3 ( I know that's not what I said earlier) and 1000 ohm for R2. Haven't blown my LED yet so it works that way too.

In truth, R1 and R2 and L1 and L2 could be dropped from the circuit altogether, they are just indicators to let you know which voltage you have selected. The indicator LEDs will light up as soon as the source select is switched, but power will not get to the firing circuit until Main power is closed. For main power I use an ATV key.

The ATV switch is actually a two position switch. I don't mean just off and on. It can be wired to where the circuit is closed with the key in and switched on. And/Or it can be wired to be closed with the key off and out. It could be used to light a green LED when the key is removed to indicate a safe state. But you would have to install a disconnect for storage so the LED wouldn't be on constantly.

There are other ways to do this using audio jacks and what not but I chose this way because I had all the stuff on hand except the ATV switch.

D1 and D2: I am not 100% what these two diodes are. They simply keep the current from backfeeding and lighting the indicator LEDs. They need to be rated high enough not to pop when current is applied. I grabbed a pack at the local Radio Shack before the closed and have been using those ever since, and that has been a good long while.

For the terminals, ST1 and ST2, speaker box terminals will work, or binding posts. I used binding posts for the rocket side with the idea I could put some banana plugs on my cables and use it that way, or just put the wires in and screw it down. Never made it that far. A 110 volt house hold socket will work great too. Just take up more room. On the external power side I used the speaker box terminals. The kind with the springs so you can use pretty much any wire on that side.

This setup works for me. Hope it helps.

If anybody sees anything wrong, chime in. I am 99.9% sure I drew it right, but everyone is prone to make mistakes.

Mikey D

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#### LithosphereRocketry

##### Pining for the Fjords
For batteries, personally I'm a gel cell fan. They're like small car batteries, but the battery acid is in gel form so you don't have to worry about them spilling. They have AMAZING current capability of ~500 amps, so the limiting factor is your wiring. The only disadvantage is that the plates are made of lead, so they weigh quite a bit - not really an issue for a launch controller though.

Just my :2:...

#### Eric

##### Well-Known Member
I use two of these 7AH sealed batteries in parallel. One would work just fine in a smaller setup. Just search 7Ah Battery and a dozen will pop up. from $8 to$25. I use used ones from time change back up lighting and fire alarm system. They work great.

#### prfesser

Can you cite a particular model? I'm seeing some gel cell bike batteries, and I'm not seeing 500 amps--only about 50 CCA.
I think the 500 amps is an exaggeration, but a 12v gel cell will light at least six motor-starters simultaneously. Probably more but I haven't tried it.

Best,
Terry
(PS: I use motor starters because BATFE sez igniters are a regulated item. )

#### LithosphereRocketry

##### Pining for the Fjords
Still, 100A is plenty... I was using the internal resistance of ~30mOhms, but that might not make sense with a lot of load.

Realistically the main thing to worry about is your wires - even a dead short won't draw 100A for most systems.

Sent from my LGL34C using Rocketry Forum mobile app

#### LithosphereRocketry

##### Pining for the Fjords
I use two of these 7AH sealed batteries in parallel. One would work just fine in a smaller setup. Just search 7Ah Battery and a dozen will pop up. from $8 to$25. I use used ones from time change back up lighting and fire alarm system. They work great.
View attachment 326175
That's the one. I only use one, but I don't typically fly clusters.

Sent from my LGL34C using Rocketry Forum mobile app

#### Rockiteer

##### Well-Known Member
Excellent resource. Thanks you!

I use two of these 7AH sealed batteries in parallel. One would work just fine in a smaller setup. Just search 7Ah Battery and a dozen will pop up. from $8 to$25. I use used ones from time change back up lighting and fire alarm system. They work great.
View attachment 326175

#### Rockiteer

##### Well-Known Member
Thanks for sharing this with everyone. Appreciate your efforts and have filed this away for future reference. Like the remote controller aspect.

I had a bit fo time today so I opened up my controller box and picked through my wires. I reverse engineered my own design by digging through the rat nest of wires, I ended up with this.

View attachment 326114

For the resistor values. I try to get 12 to 15 Ma to the LEDs. So using that and Ohm's law:

External battery is 12 volts: R2 and R3 will be 800 to 1000 ohm. The continuity LED will be a bit dimmer but it would take a bit more wiring to get two separate resistors from the two separate power sources on the continuity circuit. And it just wasn't worth it to me.

Internal battery is 6 volts: R1 will need to be 400 to 500 ohm.

Internal battery is 7.2 volts: R1 will need to be 480 through 600 ohm.

A 500 will most likely work with either the 4 C batteries at 6 volts or a rechargeable NiCad pack at 7.2 volts. I actually use 500 ohm for R1 and R3 ( I know that's not what I said earlier) and 1000 ohm for R2. Haven't blown my LED yet so it works that way too.

In truth, R1 and R2 and L1 and L2 could be dropped from the circuit altogether, they are just indicators to let you know which voltage you have selected. The indicator LEDs will light up as soon as the source select is switched, but power will not get to the firing circuit until Main power is closed. For main power I use an ATV key.

The ATV switch is actually a two position switch. I don't mean just off and on. It can be wired to where the circuit is closed with the key in and switched on. And/Or it can be wired to be closed with the key off and out. It could be used to light a green LED when the key is removed to indicate a safe state. But you would have to install a disconnect for storage so the LED wouldn't be on constantly.

There are other ways to do this using audio jacks and what not but I chose this way because I had all the stuff on hand except the ATV switch.

D1 and D2: I am not 100% what these two diodes are. They simply keep the current from backfeeding and lighting the indicator LEDs. They need to be rated high enough not to pop when current is applied. I grabbed a pack at the local Radio Shack before the closed and have been using those ever since, and that has been a good long while.

For the terminals, ST1 and ST2, speaker box terminals will work, or binding posts. I used binding posts for the rocket side with the idea I could put some banana plugs on my cables and use it that way, or just put the wires in and screw it down. Never made it that far. A 110 volt house hold socket will work great too. Just take up more room. On the external power side I used the speaker box terminals. The kind with the springs so you can use pretty much any wire on that side.

This setup works for me. Hope it helps.

If anybody sees anything wrong, chime in. I am 99.9% sure I drew it right, but everyone is prone to make mistakes.

Mikey D

#### Handeman

##### Well-Known Member
TRF Supporter
I've heard a lot of people use car jump starters. I have a compact one I got from Amazon, and it's amazing. I don't launch rockets with it, but have jump started cars several times.

https://www.amazon.com/s/s/ref=sr_n...&ie=UTF8&qid=1508588480&rnid=2470954011&ajr=0
+1

Totally agree with this! I use a car starter for power for my launch controller. I've also used it once as the battery source for the relay box on the club's HPR pads when the regular battery didn't get re-charged. It worked all day and saved the launch. I've started several cars that sat at the launch too long with radios and interior lights on. It also has a USB port so cell phones, etc. can stay charged and it works great for my LiPo battery charger to top off those batteries at the field.

It may not work any better with a launch controller then some of those mentioned above, but since it's not a dedicated launch controller battery, its use as a general power source at a launch site can't be beat. If you have a converter and a cigarette lighter port on your starter, you can power 115VAC devices too. Some starters come with built-in compressors for fixing flat tires or inflating your air mattress.

<voice of experience>In either case, I would recommend leads going from the launch controller to the starter to be different lengths. Then when they get pulled or dragged, the battery clamps of the starter won't hit together and spark and arc. </voice of experience>

How come no one has suggested using a lipo with all these posts ??
The energy density of lipo's changed the game for RC when they came out..
Why would you still want to carry lead plates ??
Why would you still want to deal with the memory of batter chemistries like lead acid..
A battery like this one --

https://hobbyking.com/en_us/turnigy-nano-tech-5000mah-3s-45-90c-lipo-pack-xt-90.html

or this one--

https://hobbyking.com/en_us/turnigy-battery-nano-tech-5000mah-3s-35-70c-lipo-pack-xt-90.html

Will make you're wire going out to the pads glow like an ignitor wire if you short it...
It's super light,, easy to carry and move,, doesn't have a memory,,
they don't self discharge like all of the other chemistries do,, and has more capacity then you would need in a day's flying...
The biggest thing to me is that the tendency with a battery for this purpose is that all the time it isn't being used it's going to be left on a charger,,
it will "learn" that and performance will suffer greatly because of it..
These batteries will need to be charged with a balance charger,,
when the balance charger is done it will turn off and the battery will be ready for the next days flying even if that's 2 months away...

How come nobody likes these lipo's ???

Teddy

#### dhbarr

##### Amateur Professional
LiPos ain't great in the cold.

#### Handeman

##### Well-Known Member
TRF Supporter
How come no one has suggested using a lipo with all these posts ??
The energy density of lipo's changed the game for RC when they came out..
Why would you still want to carry lead plates ??
Why would you still want to deal with the memory of batter chemistries like lead acid..
A battery like this one --

https://hobbyking.com/en_us/turnigy-nano-tech-5000mah-3s-45-90c-lipo-pack-xt-90.html

or this one--

https://hobbyking.com/en_us/turnigy-battery-nano-tech-5000mah-3s-35-70c-lipo-pack-xt-90.html

Will make you're wire going out to the pads glow like an ignitor wire if you short it...
It's super light,, easy to carry and move,, doesn't have a memory,,
they don't self discharge like all of the other chemistries do,, and has more capacity then you would need in a day's flying...
The biggest thing to me is that the tendency with a battery for this purpose is that all the time it isn't being used it's going to be left on a charger,,
it will "learn" that and performance will suffer greatly because of it..
These batteries will need to be charged with a balance charger,,
when the balance charger is done it will turn off and the battery will be ready for the next days flying even if that's 2 months away...

How come nobody likes these lipo's ???

Teddy
Teddy,
I have nothing against the LiPos, but for an overall battery for use as a launch controller power source, I believe the car starters can't be beat. The LiPos will be dedicated batteries for the launch controller, a car starter is a general purpose power source that can be used for many different things, besides the launch controller. I do believe you can get small compact car starters using LiPos now. Even better.

#### Eric

##### Well-Known Member
And the 7Ah sealed lead acid ones I use are cheap to free. And easy to charge and maintain.

Sent from my VS988 using Tapatalk

LiPos ain't great in the cold.
All battery chemistries performance declines in the cold...
None are different...

Teddy,
I have nothing against the LiPos, but for an overall battery for use as a launch controller power source, I believe the car starters can't be beat. The LiPos will be dedicated batteries for the launch controller, a car starter is a general purpose power source that can be used for many different things, besides the launch controller. I do believe you can get small compact car starters using LiPos now. Even better.
Rich,,
You'll never touch the size,, weight and low bulk of a lipo..
I still don't get why you'd use any battery chemistry for any purpose other than a lipo..
But no chemistry is easier to charge and maintain than a lipo...

Teddy

#### dhbarr

##### Amateur Professional
All battery chemistries performance declines in the cold...
None are different...
Yeah, but some are more equal than others ^_^

Yeah, but some are more equal than others ^_^
The only chemistry there that is an option at all is lead acid...
I would take the lipo over the lead acid battery any day no contest...

Teddy

#### j.a.duke

Ive used the 12V 7AH batteries, but they get heavy really quickly when you are hand carrying them (IIRC, its about 1 pound per AH for weight). I changed to a 12V 1.2AH and have been able to get 50+ launches from the same battery (couple of different sessions, but didnt charge the battery in between).

An example of what Ive used is: https://www.batteryplex.com/toyo.cfm/m/6FM1.2

My controller is a modified Estes rectangular block that has a pair of wires to the battery, longer leads to the pad and an LED for the continuity check. I think I added a resistor to drop the voltage for the LED, which also makes the system safe for those low amperage igniters like the Quest Q2G2s.

I havent looked at the design posted, but check the current delivery before the launch button is pressed. I dont recall what the limit on the Q2G2s are, but its pretty low.

Cheers,
Jon

#### Steve Shannon

##### Well-Known Member
TRF Supporter
Ive used the same eight 7 Ah SLA batteries for the past 15 years for our club launch batteries. Battery memory is more related to NiCad batteries than SLA. Ive had to replace one in all that time. I never leave them on the charger. I charge each one for 10-30 minutes the day before a launch.
I agree that lipo batteries would be lighter and have less internal resistance, but these have worked great. A couple years ago the company I worked for replaced the batteries in a large ups and I picked up another 200 of the 7 Ah SLA batteries that are 5 years old and have been very well maintained. I dont see myself buying lipos for the club.
They light every cluster weve ever tried.

#### Handeman

##### Well-Known Member
TRF Supporter
The only chemistry there that is an option at all is lead acid...
I would take the lipo over the lead acid battery any day no contest...

Teddy
Teddy, It's not the battery tech, it's how it's packaged that makes the difference. A car jump starter not only has the battery, but usually includes USB charger ports, flash lights, etc. Some have a compressor and cigarette lighter socket you can plug a 12VDC to 115V AC power inverter into and charge/run your laptop.

If you want to stick with lipo tech, then check out the \$100 unit at Walmart, 3lbs lipo that will give you 20 starts on a single charge along with flash light and USB ports. Genius Boost

The other thing with the jump starters, most have the AC prongs built in so all you need is an extension cord to charge them, no LiPo charger required.

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#### rharshberger

##### Well-Known Member
We use the jumpstarters (SLA type) and every so often a battery will fail, at least once we have replaced the battery no issue,it was just a matter of opening the unit and locating a similar battery. As Handeman said they are also very easy to recharge either at home or on the field using a generator.

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