Lithium Ion battery for the E/X-Mag?

[rukh013]

Hell if we can't fit them in the existing emag/xmag battery case can we get dimensions and maybe change the pack geometry?

maybe bump the front of the pack out?

[knownothingmags]

KNM: wait wat? you make wat in house that you cant bring them to the public? im confused?

2xfast:a battery store can make you a battery for your Mag pretty cheap.

I don't know the details of how they are made, I have only seen them made.
I just can back them with the funds they need.

[knownothingmags]

I've tried shopping around the RC battery places (specifically the one linked in this thread earlier). No dice. As I mentioned the trick is the C rating. Getting something that can dump enough amps fast enough requires non AAA shaped cells.

c rating isn't just how fast the pack will dump its juice, its how fast the battery needs to dump it,
I have rc packs that can dump at 150-200 c rating, they have never ever dumped that high, but they can if needed,

c rating is the allowance of dumpage.

[2xFast]

OK poor choice of words. Was my may wrong? mAh capacity X C rating = available amps?

150 c is really damn high! I don't think anything that powerful is available in our size / weight range. If this isn't somewhere around half the weight of the stock pack there's probably not much point in doing it.

c rating isn't just
how fast the pack will dump its juice, its how fast the battery needs to dump it,
I have rc packs that can dump at 150-200 c rating, they have never ever dumped that high, but they can if needed,

c rating is the allowance of dumpage.

[knownothingmags]

OK poor choice of words. Was my may wrong? mAh capacity X C rating = available amps?

150 c is really damn high! I don't think anything that powerful is available in our size / weight range. If this isn't somewhere around half the weight of the stock pack there's probably not much point in doing it.

no, you are right, you would be fine with 20-40 c rating, actually that should be plenty.

[JimBobFett]

I see many mentions of battery configurations with "similar" voltages and currents listed. I am an EE. If someone could post what the OEM battery's voltage and current requirements are, I could lend a hand.

There may be an electro-mechanical solution that is possible that could replace the need for batteries all together. A small pneumatic generator could be used to charge a capacitor with every shot. Standby power could be maintained with a smaller battery.

[athomas]

The AGD voltage is 16.8VDC for that solenoid, which translates to about 6 amps of peak current draw but for much less duration than the 100ms pulse at 14VDC listed on the spec sheet. Most LiPo cells can produce that current output. The 5 cell pack is the way to go for LiPo. At the low end of the voltage range a four cell pack would provide a really low voltage which would cause the solenoid activation to become unreliable.

[2xFast]

I see many mentions of battery configurations with "similar" voltages and currents listed. I am an EE. If someone could post what the OEM battery's voltage and current requirements are, I could lend a hand.

Here's the solenoid

http://www.solenoidcity.com/solenoid/tubular/s-15-75p1.htm

Here's the pack:
Stock weight: 185g
Nominal output of 16.8V
650 mAh stock, my rebuilt one is 850mAh (still NiMH)
Again, I believe this pack can do ~22 amps
(it's 14 AAA sized cells wired in series)

[GoatBoy]

I think you guys are making things way more complicated than need be, and trying to overpower things as usual while still fumbling around in the dark somehow.

1. Get the exact dimensions of the current pack. No dancing around, pull out a set of calipers and actually measure the exact thing and post it, or post the exact topology of the 14 cells, and make sure that they really are AAA cells (44.5mm x 10.5mm diameter).
2. Get the exact dimensions of the space you can fill. No dancing around, pull out a set of calipers and actually measure the exact thing and post it.

My recommendation would be to go with a 4s LiPo pack. No boost, no PCB protector -- just go straight in.

Someone should run some tests, but I think you will get away with a 4s pack.

Were all the E/X-Mag electronics, solenoid, and parameters chosen during the age of L7 bolts? Because a properly tuned L10 bolt may lower the operating requirement enough to reliably operate off a 4s pack for the majority of the useful charge.

[athomas]

Someone should run some tests, but I think you will get away with a 4s pack.

Were all the E/X-Mag electronics, solenoid, and parameters chosen during the age of L7 bolts? Because a properly tuned L10 bolt may lower the operating requirement enough to reliably operate off a 4s pack for the majority of the useful charge.

A 4S pack has a low end voltage of 13.2VDC compared to a low end voltage of 15.4V for NiMh. That's a 27% reduction in available power when the battery pack gets towards the lower end of its usable range.

The lower force on the sear is somewhat offset by the increased pressure pushing down on the on-off pin. The resulting sear activation force is not much different on the level 10 when compared to the level 7.

[GoatBoy]

A 4S pack has a low end voltage of 13.2VDC compared to a low end voltage of 15.4V for NiMh. That's a 27% reduction in available power when the battery pack gets towards the lower end of its usable range.

The lower force on the sear is somewhat offset by the increased pressure pushing down on the on-off pin. The resulting sear activation force is not much different on the level 10 when compared to the level 7.

Did you mean "dominated by" instead of "offset by"? There's no "offset by" involved here. If the system was designed with L7 in mind and you straight dropped a tuned L10 in there, the force goes down.

If it's still dominated by the on/off, I can understand, but there's only one direction that force can go, and that's down.

The threshhold voltage needs to be determined first. That is the critical point, and until you figure that out, you're all pretty much just talking in circles. I'd test it myself, but I don't own an E/X-mag. I might be able to borrow one... but I'm not feeling super motivated. I just feel bad watching you guys go around in circles.

Assuming the spec from 2xFast is accurate (thanks for those numbers), the solenoid is spec'd to run at about 80w at 14.6V. Let's assume that's correct.

For a 4s 500mah pack, that's maybe around 12C discharge, which is pretty manageable for a modern LiPo battery. Actually, that's a cakewalk.

A decent pack is going to maintain 3.6V per cell over at least 3/4 of its charge. You can find the discharge graphs all over the RC forums to verify this.

That puts a 4s pack at 14.4V or greater for 3/4 of its charge.

If it were me, I wouldn't care about that last 1/4 of charge. I don't carry 5 games worth of air on my person when I know I'll be back in staging after 2-3 games. I don't carry 5 games worth of paint on my person when I know I'll be back in staging after 2-3 games. Anything battery operated... I'd be perfectly happy swapping a battery out mid-day if it meant smaller, lighter, faster. That's what I do with my helmet camera batteries. Except my helmet camera doesn't have a "mechanical mode". *cough*

[athomas]

"Offset" definition: Counteract (something) by having an opposing force or effect: "the deficit was offset by capital inflows".


The forward force applied to the sear decreases when you install the level 10 compared to when you have a level 7. That force only negates some of the friction of the sear sliding off the bolt. The chamber pressure increases by 50% so the downward force on the back of the sear increases by that much. So, the result is that the force exerted by the on-off pin increases by 50% and the friction force is decreased by X amount. I'm guessing the friction reduction is about the same as the on-off increase resulting in a similar pull force requirement.

The maximum force the solenoid can exert at any given voltage is measured when the solenoid is fully pulled in. As the distance from bottom increases, the solenoid force decreases. You can see it on the charts for the solenoid. The distance of pull for the sear to safely clear the bolt is about 1/8", so the solenoid must pull 1/4" because the solenoid arm is approximately twice the distance from the pivot as the on-off contact and the bolt catch. At the rated 14.6V, the solenoid can pull 36oz of force from a distance of 0.25 inches. The on-off part results in approximately 32oz of downward force on the back of the sear which translates into 16oz of solenoid force requirement. At the low range of voltage for the 4S LiPo, the force would be 26oz of solenoid force based on the charts. The sear rotational friction from the forward bolt force and other mechanical frictions results in the rest of the pull force requirement. That is minimal due to the level 10 setup, but there is some. I'm not sure how much. It should be measured.

The problem is not that the solenoid won't do the job using a lower voltage. It might. The problem comes when you combine lower voltage, longer pull, greater friction, and a few other unknowns due to tuning and setup that are not perfect. Using a 4S LiPo, you have less than 60% reserve allowance for things that aren't ideal. This number is further reduced if you use higher chamber pressures for shorter or longer than ideal barrels, stiffer bolt springs, etc.

3.65V is the 50% charge point of a LiPo cell. The discharge of a LiPo is fairly linear in its operating range.

[GoatBoy]

The maximum force the solenoid can exert at any given voltage is measured when the solenoid is fully pulled in. As the distance from bottom increases, the solenoid force decreases. You can see it on the charts for the solenoid. The distance of pull for the sear to safely clear the bolt is about 1/8", so the solenoid must pull 1/4" because the solenoid arm is approximately twice the distance from the pivot as the on-off contact and the bolt catch. At the rated 14.6V, the solenoid can pull 36oz of force from a distance of 0.25 inches. The on-off part results in approximately 32oz of downward force on the back of the sear which translates into 16oz of solenoid force requirement. At the low range of voltage for the 4S LiPo, the force would be 26oz of solenoid force based on the charts. The sear rotational friction from the forward bolt force and other mechanical frictions results in the rest of the pull force requirement. That is minimal due to the level 10 setup, but there is some. I'm not sure how much. It should be measured.

Is 32oz the max force? Or is it the typical force? If I'm not mistaken, the RT valve produces max force when it decides to recharge, but that's not the same force as when the system is at rest, ready to fire. So the worst case for the on/off force implies that you're trying to pull it at the worst possible moment, which might not be particularly realistic.

Measurements are great and all, but there's probably a real fast way to test this. Mag, variable power supply, go.

I mean, really, even by your numbers, it sounds like you guys got this.

The problem is not that the solenoid won't do the job using a lower voltage. It might. The problem comes when you combine lower voltage, longer pull, greater friction, and a few other unknowns due to tuning and setup that are not perfect. Using a 4S LiPo, you have less than 60% reserve allowance for things that aren't ideal. This number is further reduced if you use higher chamber pressures for shorter or longer than ideal barrels, stiffer bolt springs, etc.

True, if I wanted to make this work for everybody, I'd overpower and overdesign things as AGD is wont to do.

But by now, I'd consider this more of an "expert level" mod, and you guys might as well aim for the bleachers.

[athomas]

The 32 oz of force exerted by the on-off pin is the force when the chamber is full and only the small diameter of the pin has any affect. This is the required force to push the pin up into the valve.

The max force applied to the pin during recharge is much larger than this (approximately 140oz) due to the larger size of the head of the on-off pin, but at that time the plunger will be fully engaged in the solenoid and it will be developing maximum pull force of over 76 oz which equals 152oz due to the 2x distance of the lever. This is all measured at 14.6V. At 13.2V, the force delivered by the solenoid when fully engaged would be 73oz or 146oz at the pin. If the tank regulated pressure is higher than 850psi, then the force applied down on the sear will be even greater than 140oz. The maximum pull force for the solenoid is also measured with the solenoid fully engaged. If the solenoid plunger is adjusted such that it doesn't bottom out, then the applied force is less than that. A 0.04" gap where it doesn't bottom out will reduce the applied force by about 15%.

Using a 4S cell pack would definately be an "expert level " mod due to requiring everything being adjusted perfectly and not using high output tanks. Use a 5S cell pack and you have a bit more power than you have now, and are guaranteed that it will always work for all conditions.

[2xFast]

I'll pickup a 4S pack as well and see if that does the trick. It certainly would be MUCH simpler to source.