4 Pad Relay Controller - Full Functional test

October 29 2018

Today I just finished the 100-foot interface cable for my controller; to keep within the rules for my upcoming HPR launch here in South Dakota. So far, I just been using my original 50-foot cable and just did LPR launches. I was pretty pleased with the way it performed as I was afraid the voltage drop would cause big problems. All the power for the controller comes from the battery in the Pad box; and the voltage drop calculator I used had it at about 9.7vdc all the way back at the controls. The control circuits are of course very low current, with the high current output through the Arm and Launch relays. The automotive side marker lights simulate the igniters. I performed a complete functional and safety check of the Pad Box and Controller.

I forgot to video all the safety checks I did first, but at least i remembered to take pics and some video.

That's the cord reel I found for like $4 dollars.... Plenty for the lightweight 100 foot cable.



This is what it looks like with all igniters hooked up and "Mode Select" in "Test"



This one is with "Mode Select" in "Arm" and all 4 pads selected - The Launch button illuminates but what you can't see, are that the "Pad Arm" LEDs are actually flashing. Should be ready for some Level 1 HPR flights, as well as Model Rocket flights


Test Results: Fully functional

Battery 12.7vdc 12AH

11.5vdc at Master Arm relay coil with Mode Select in “Igniter Test”

10.4vdc at Master Arm relay coil with Mode Select in “ARM”

9.8vdc at Master Arm relay coil with all pads “Armed”

Battery-Low light illuminated with 3 simultaneous pad launches.

Voltage drop from 100 ft cable is enough to cause battery the low light during multiple simultaneous launches, but does not affect power to igniters.

So anyway; when it was all said and done, I was happy and thought I would share it with the forum. Here is a video of the test:

Nice job but those voltage drops are excessive, can you post a schematic? Also what is the current draw on the simulated igniters ?

SG

Sghioto,

Thanks, After i estimated using an online calculator for 22ga wire, I didn't think the voltage drops were that bad.
Considering the battery power starts at the pad box and goes 100 feet to the control box then back 100 feet to the pad box where i checked it at the Arm Relay. To answer your other question I have not yet measured the current draw on the simulated igniters (12v Automotive Side Marker bulbs.) I will run the test Thursday using Q2G2 igniters again and put my amp meter in line. Here are the schematics. Thank you for your input

Glasspack

Just a few more photos in case you want to see it......................


The pad leads that plug in are about 15 feet long made with heavy duty extension cords, soldered to smooth jaw copper clips




The black heat sinks on the right are for the High current (25Amp) Schottky diodes used to eliminate any feedback during launch from one pad to another pads test circuit. My wonderful friend and fellow aircraft electrician that helped me all the electronics passed away two years ago from Cancer, so I can't ask him to help me remember the exact anomaly we had that caused us to use the diodes. But, i believe we would get a false test light on a pad that wasn't even hooked up.

Ooops..... Here is the correct Pad Box Schematic
The other one did not include the 4 High current Schottky Blocking Diodes.

Glasspack said:

believe we would get a false test light on a pad that wasn't even hooked up.

Click to expand...

That is correct using this design with allows continuity to be verified at the controller. I don't see any problem with the design although that battery pack looks less the 12 ah. I'm curious,what does the battery voltage at the pad box measure when all four pads are armed and the current draw
SG

SG, If its not 12 AH then the unit is packaged wrong and is deceiving. Perhaps a deep cycle battery would be better for model rocketry but it can deliver 20A to an igniter. I have tested it with pad leads shorted together to test wires and trip the circuit breaker. The relays are 30 amps and I wanted to make sure the breaker would trip before it damaged any wiring or components. Let me go read the voltage and try to get some amp readings.

SG,
I was able to read total current with all four Q2G2 igniters hooked up and in test.
The meter was hooked up at the battery so I was reading the total current on the system, not just the current at the igniters. But the total current for all 4 in test was 375 MA. Once I went to Arm which would have flashed the tsst lights at the controller the meter died I think, because it went all zero. So I moved on and tested the all fire circuit.

For some reason the Test Fire video will not load on my end. Besides that I see the battery is correct at 12 ah. It just seemed smaller in the the other pictures when looking straight down. That battery should be sufficient. Did you get a chance to read the battery voltage when fully armed ?
SG

Anyway I calculate the voltage drop at the master arm relay coil at around 11.5 volts with the system fully armed and a fully charged battery. So I'm wondering if the battery is not fully charged or not holding a charge if the coil voltage is down to 9.8 volts

That is a good point the battery is a couple years old and spends a long time use and lately has been in the garage subject to temperature swings like a car battery would. The new testing i just did so far shows a .2 vdc drop through the Blocking diode at the mode Select switch.....Maybe I selected to small a diode. Anyway the The battery is now at 12.5 vdc and at the igniters the power is 12.41vdc so that is just .1 drop from the battery, through the relay, down the pad whip and at the igniter. let me read the battery voltage and coil voltage when fully armed.......

Ok so the battery has been sitting for a day or two with the power LED on. So here are test results:

Battery -12.6vdc
Arm relay coil in "Test" - 11.7
Arm relay coil in "Arm" - 10.6vdc
Arm relay coil with all four pads Armed - 9.8vdc
Each Arm relay coil - 10.5vdc

On a side note I did recently drain the battery by using all four test lights (Automotive side marker bulbs) in less than 30 minutes. Then recharged it for about 24 hours. I use a Schumacher XM1-5 Battery Maintainer. Maybe I should try a new battery.... Think I could find one with even more Amp Hours that would fit in the box?

[/Quote] Maybe I should try a new battery...[/QUOTE]
Probably so. I'm still curious though, is the battery voltage 12 volts or more when the system is fully armed ?
SG

At the Battery, yes, it is still at its full charge state. Also at the igniters the voltage drop is very minimal ...like .1.
But that is because of the way it's designed and wired, to maximize voltage and current at the pads.

Do you think the Battery should be more than 12.6vdc when fully charged?

Glasspack said:

Do you think the Battery should be more than 12.6vdc when fully charged?

Click to expand...

No that is the correct voltage. Just seems odd the amount voltage drop on the
arm relay coil. For example in the "test" mode the arm relay is the only device drawing any significant current and the voltage drop is .9 volts (12.6-11.7) according to your measurements. 200 ft of 22 gauge wire has a resistance of 3.23 ohms so the current drain would have to be 272 ma (.272 x 3.23) to drop .9 volts. That seems excessive unless the relay coil draws that much. Just my 2 cents worth. Almost forgot, are all of the continuity LEDs in the control box on when in the "test" mode?
SG

Yes SG, the 4 bright green Pad Continuity LEDs all flash "Armed" when reading the 9.8 vdc at the relay coil. Its higher in test (11.7) because power is not going through the Blocking Diode at the Mode Select Switch. Also none of the 4 flasher (Vibrator) circuits are enabled yet. At least that's my understanding.

Here is where I got the numbers from. https://www.calculator.net/voltage-drop-calculator.html
I estimated about 0.5a of current for the arm circuit. I says use only one way measurement, but it had to be 200 feet since the power comes to the control box and then back to the pad box to the relay coil. Of course it was all based on 12vdc; not 12.6vdc, which was the fully charged voltage reading I actually got on the battery.


WEB SITE Result
Voltage drop: 3.23
Voltage drop percentage: 26.90%
Voltage at the end: 8.77
Please note that the result is an estimation based on normal condition. The actual voltage drop can vary depend on the condition of the wire, the conduit being used, the temperature, the connector, the frequency etc. But, in most cases, it will be very close.


I drained the battery last night and will fully charge it again one more time to prepare for my launch after Thanksgiving. I am still hopeful the FAA will approve my request.

Glasspack said:

I estimated about 0.5a of current for the arm circuit.

Click to expand...

Based on what? I couldn't get a part number for the relay from your pictures but it does look like those PCBs include coil driver circuits. If you used those the drive current would be greatly reduced.

When calculating voltage drop don't forget that while each relay coil has its own individual 100' wire run from the control switch, they all share a single 100' wire run from the battery to those switches.

I really didn't think I was pulling that much current to operate the relay....... I just estimated .5 A so I could calculate the voltage drop. I did replace the relays with 30A relays, but the control PCB is the same. The relay boards are from Sparkfun. https://www.sparkfun.com/products/13815 They operate on 5vdc to control the 12vdc to the igniters.
I just used the 30A relays from Mouser, All Electronics or Digikey ......... The relay coils are rated at about 185mA.

Anyway I cannot find the invoice from the relays I bought, so I can only estimate. But the battery is fully charged and the functional test proved it works very well, and has plenty of juice where it counts ! I noticed this morning when I pulled the charger off, the battery is at 13.4vdc. I have tested it many times and tried to get it to act unsafe.
So far it has proven to be a safe and reliable design.

Glasspack, UhClem is correct you should use the drive circuit to control the relays. It kinda sucks that the low battery indicator activates when the battery is actually fully charged.
SG

I do have jumpers in the input control section of the relay PCB because I think the higher amp relays were 12vdc coils not the 5vdc coils of the original 20A relays. Now I want to look closer. As for the low battery light...... When the battery was fully charged during that test I was talking to you about, the low battery indicator only lights up when I am reading like 9vdc at the controller. And that only happens with my 100 foot cable while launching 3 pads at once.
I am not sure if I misstated something, or you misunderstood my test.

So between the two of you do you think the voltage drop is excessive at about 3vdc from the battery to the controller back to the relay coils. A total of like 200 feet of 22 awg stranded wire. ??

Thank you both so much for your input !
Paul

Glasspack said:

do you think the voltage drop is excessive at about 3vdc from the battery to the controller back to the relay coils.

Click to expand...

Paul, not at all if the relay coils are drawing 185ma or more. Yes I did understand correctly about the low battery indicator.
According to the specs on the those Sparkfun boards the relays draw about 150 ma and are designed for 5 volts. If you are using 12 volts those relays will be drawing over 300 ma.
Just to make sure, you have replaced the 5 volt 20 amp relay coil on the Sparkfun board with a 12 volt 30 amp relay, is that correct?
Steve

I have to double check Steve, because I can't find my invoice for the relays. I built it about 3 years ago.
I am pretty sure the coils were 12vdc on the 30a relays i put in. My next one I will use the basic design I have here but incorporate wireless interface......that way I can eliminate the voltage drop all together !!
I have had something like this in mind: Using the modules to activate relays to maintain enough high current at the igniters. And have enough in the design to be able to read continuity, Key lock out and
all operate safely of course.

https://electricmatch.com/pyrotechnics/see/2/5/alpha-firing-module

Paul .........