Home Build M4 Overheating Batteries - Help/Advice Welcome

[Caber77]

HI All,

Firstly i'll introduce myself as i usually sit lurking in the background, scanning other peoples threads/posts and researching/ collating all the info i can to help me with my own project builds.

So.. My name is Lee and go by the name of CABER - yes the Scottish pole and thats because im Scottish with a Polish family decent. Been playing Airsoft for a little over 2 years but not new to pew pew by any means. Have been seen on the Scottish fields for many a year but previously slinging paint - yes ive converted.....

Also captain of our team - The Nomads (probably a few Nomads teams out there) but we genuinely dont have a home site and tour round as many Scottish sites as we can so the name is quite appropriate.

Intro over....

My question is as follows and i'll try to give as much info as i can.

I've been building a project gun for quite some time (not the first ive done) and im running into problems with 11.1v 1450 20C / 40C Lipo batteries overheating and discharging within around 2-3 high-cap mags on semi or 1 mag on full auto.

The build I have in the GB;

SHS 12:1 gear set (with sector chip fitted)

LONEX 8mm SS bushings

SHS 14 tooth full metal rack piston

SHS ball bearing Piston and Cylinder head

SHS Air Nozzle

Gate Titan Advanced ETU/Mosfet

Guarder SP110 spring

SHS HT Motor

Madbull SS 300mm 6.03 inner barrel

MAXX Tracer Hop

G&G Green cold resistant bucking

The AEG runs at a steady (ish) 345fps and is averaging 47 (ish) rps, I have a chrono at home so able to test this. Checking the Titan on my phone im drawing around 94amps peak current, 44.5 on semi and 35.7 on auto so pulling way too much juice obviously causing the early death of the batteries. Done the same thing when using a team mates 30C / 50C battery - killed his just as quick.

When building the GB i shimmed the gears starting with the motor height pinion gear against the bevel gear and went from there. Ive done this practice on every GB that ive build and never had any issues with motor height or shimming. and I'm very confident that had it shimmed very well.

As a result of the overheating i decided to shim it again just in case i was a bit tight on the gears and this time ive shimmed just a little slacker and get a comfortable 2.5 - 3 full rotations of the sector gear before it stops. Actually used a different GB shell (JG reinforced) just in case there was any issues with alignments of the bushing too.

Ive tried both SHS HT and JB HT motors in it along with a stock G&G 18k motor that came out my sons AEG when i modified that for him. I know (as well as i can do) the current SHS HT motor is good as it was only bought in February.

Piston is full stroke and pre holed so no swiss cheese going on here and no short stroking either.

Being extremely confident that my motor height and shimming are spot bollock on (please don't suggest this to be the issue as I've shimmed it a couple of time to triple check) and that the Titan and SHS HT motor were both purchased in Feb so I no there are no issues with wiring (previous basic trigger was on 16awg and still had the same issues) and I use only Deans connectors does anyone have any legitimate suggestions as to what can be causing the overheating of batteries and sending them to their graves?

As a possible solution ive ordered a Guarded SP90 spring to see if the reduction in resistance transferred through gears - motor - battery has a positive effect on the battery life without causing a negative effect of PE. Obviously the titan has AB so should by rights assist with this anyway.

If that doesn't help then I'm thinking of short stroking and dropping the 110 back in but don't really want to lose volume.

Any advice would be appreciated.

Thanks

 

[concretesnail]

As a quick guess, assuming that there is nothing in the gearbox causing excessive strain then it is just the draw that the electrical components require. 

Ias you are already using 11.1 upping the voltage to reduce amp draw isn't the first thought for a fix so I'd suggest that the battery packs aren't up to task and that they aren't able to cope, suffering sagging voltage and increased draw.

The first I'd try is to look to run a higher draw pack and go from there.

 

[Caber77]

As a quick guess, assuming that there is nothing in the gearbox causing excessive strain then it is just the draw that the electrical components require. 

Ias you are already using 11.1 upping the voltage to reduce amp draw isn't the first thought for a fix so I'd suggest that the battery packs aren't up to task and that they aren't able to cope, suffering sagging voltage and increased draw.

The first I'd try is to look to run a higher draw pack and go from there.

Thanks for the reply, Ive tried using a mates battery which has a higher draw than mine, his are 30C/50C where mine are 20C/40C and it had the same effect of the battery being killed within a matter of moments. Are you suggesting I try something bigger than 50C continuous?

 

[Alimcd]

47rps on a 110 spring with no teeth off piston release side or sector?

Not sure how the piston hasn’t been completely annihilated yet. The M90 spring is going to return the piston far too slowly and you’ll almost certainly strip the piston, assuming it’s the part that fails first.

Using SittingDuck’s formula, a totally efficient SHS HT/12:1 combo should give you c.30rps so maybe they’ve shipped you a high speed motor instead?

It would certainly account for it brutalising the batteries and drawing high amps.

AK2M4’s site also had something in it about the SHS HT/Titan potentially being problematic with AB enabled, could be worth a try disabled to rule it out?

 

[Asomodai]

By SHS High Torque. What do you mean? They advertise the 16TPA one as High Torque, but in actuality it is more "balanced". A 16TPA Motor will struggle with 12:1 gears.  It's more suited to 18:1 and 16:1.

 

[ak2m4]

47rps does sound very high, what colour is the motor can?

AK2M4’s site also had something in it about the SHS HT/Titan potentially being problematic with AB enabled, could be worth a try disabled to rule it out?

I don't think it's anything to do with his amp draw issue but AB in general isn't great for motors, had several customers with new failed motors using the adaptive breaking feature.  Massive amounts of carbon dust build up.

 

[Iceni]

11.1v 1450 20C / 40C Lipo batteries overheating and discharging within around 2-3 high-cap mags on semi or 1 mag on full auto

47 (ish) rps

94amps peak current, 44.5 on semi and 35.7 on auto

Right lets run the numbers on those.

1.45Ah / 35A is 2 minutes 29 seconds of runtime (0.04hours). (24C)
1.45Ah/ 45A is 1 minute 56 seconds of runtime (0.03hours). (31C)
1.45Ah/ 95A is 54 seconds of runtime. (65.5C)

Your batteries are rated for:
1.45 x 20 = 29 amps continuous.

1.45 x 40 = 58 amps peak.

You are drawing double your peak amperage and over your continuous amperage in all instances.

I'd be very surprised if those batteries are even holding the correct charge any more the chemicals are probably well on the way to a catastrophic breakdown. I'm not surprised they only give you 1 mag. I am surprised you don't get a nasty fireball at the end of that.


Increasing C multiplier rating isn't enough. You need to increase C multiplier and capacity.

Assuming you can find a 25/50 3s 11.1 you are going to need at least:

95/50 = 1.9Ah (1900mAh) Add in a tolerance for the overheads and your looking at perhaps a 2.2Ah (2200mAh) capacity.

@2.2Ah:

2.2/35 is 3 minute 46 seconds. (16C)
2.2/45 is 2 minutes 56 seconds. (20C)
2.2/95 is 1 minute 23 seconds. (43C)

So look for something along these lines.

11.1 25/50C 2200mAh.

Assuming 11 seconds of shooting per mag (500/45). You should have enough juice for at least 7 mags, potentially 20 mags per battery ( 3,500 to 10,000 bb's).

 

 

[James Baker]

I have a similar issue, unfortunately I can’t offer much useful advice but would like to follow to see what is causing yours.

 I have the issue with SHS high speed motor with 13:1 gears, now swapped for 16:1 gears. Basic gate mosfet with no AB. It could just be these motors?
I should note, I’m still learning lots so while I have shimmed and reshimmed I can’t guarantee that’s not my issue but I’m pretty sure.

All the best

James

 

[Caber77]

By SHS High Torque. What do you mean? They advertise the 16TPA one as High Torque, but in actuality it is more "balanced". A 16TPA Motor will struggle with 12:1 gears.  It's more suited to 18:1 and 16:1.

HI Asomodai, i honestly couldnt say regards the TPA. The motor is certainly maked up as being HT rather than HS. As mentioned in my earlier post though ive tried a few different motors and the results are pretty much the same regardless of which one i have in.. in terms of the battery. RPS varies obviously between the different motors ive tried. 

47rps on a 110 spring with no teeth off piston release side or sector?

Not sure how the piston hasn’t been completely annihilated yet. The M90 spring is going to return the piston far too slowly and you’ll almost certainly strip the piston, assuming it’s the part that fails first.

Using SittingDuck’s formula, a totally efficient SHS HT/12:1 combo should give you c.30rps so maybe they’ve shipped you a high speed motor instead?

It would certainly account for it brutalising the batteries and drawing high amps.

AK2M4’s site also had something in it about the SHS HT/Titan potentially being problematic with AB enabled, could be worth a try disabled to rule it out?

I can certainly try it with the AB turned off but i dont think that will make any odds as the TITAN was only recently fitted and i had the same issue prior to installing it. Before i put the TITAN in there was only a basic trigger switch and no mosfet. It could just be down to battery discharge i guess.

Right lets run the numbers on those.

1.45Ah / 35A is 2 minutes 29 seconds of runtime (0.04hours). (24C)
1.45Ah/ 45A is 1 minute 56 seconds of runtime (0.03hours). (31C)
1.45Ah/ 95A is 54 seconds of runtime. (65.5C)

Your batteries are rated for:
1.45 x 20 = 29 amps continuous.

1.45 x 40 = 58 amps peak.

You are drawing double your peak amperage and over your continuous amperage in all instances.

I'd be very surprised if those batteries are even holding the correct charge any more the chemicals are probably well on the way to a catastrophic breakdown. I'm not surprised they only give you 1 mag. I am surprised you don't get a nasty fireball at the end of that.


Increasing C rating isn't enough. You need to increase C and capacity.

Assuming you can find a 25/50 3s 11.1 you are going to need at least:

95/50 = 1.9Ah (1900mAh) Add in a tolerance for the overheads and your looking at perhaps a 2.2Ah (2200mAh) capacity.

@2.2Ah:

2.2/35 is 3 minute 46 seconds. (16C)
2.2/45 is 2 minutes 56 seconds. (20C)
2.2/95 is 1 minute 23 seconds. (43C)

So look for something along these lines.

11.1 25/50C 2200mAh.

Assuming 11 seconds of shooting per mag (500/45). You should have enough juice for at least 7 mags, potentially 20 mags per battery ( 3,500 to 10,000 bb's).

 

Iceni, thanks for this on the batteries. gotta be honest and say the calculations have baffled me and i'd love to know how you work this out. Im not for moment questioning you on this, simply stating that i dont understand it and would like to know more. Im curious as to how you work out the ratings.

Certainly seems logical that i need to carry a car battery on my back to supply the juice!!

 

[Sitting Duck]

Guarder SP110 = M120 Spring, so potential 394fps ???

47rps ???

I could see you clipping near 27rps on 7.4v,

then maybe 41rps on 11.1v - but 47 is going some,

Though a beefy C LiPo will give you extra zest,

The flip side is the fancy ETU's tend to skim a bit of power,

(each diode nicks 0.5-0.7v, turn on/forward voltage).

30k ÷ 12.75 (ratio) will give you about 23.5rps,

Squeeze a bit more out on 16awg/deans, shim well about 27rps,

x 1.55 = maybe 42rps & I've smashed a piston at that speed

even though it was short stroked 3 teeth ???

So 47rps is going some, perhaps questionable,

given that ETU's skim some juice

& motors should make a difference...

A 30k motor Vs a 18k G&G there will be a difference.

Also forget bells & whistles a second...

Set the Titan to do basic stuff, no AB, precock, burst etc...

Grab a standard RC power meter,

Plug that in and run a 5sec auto burst on 7.4v,

NB 7.4v not 11.1v to check amps on meter in auto,

coz the way the fancy MOSFETs report stuff varies.

Yes the surge from still will be 80-90 amps,

But overall the draw over a 5 sec period should,

be below 20, about 17 amp if done well 12:1 30k.

Draw will be lower on higher TPA motor,

But G&G 18k grey will struggle on 7.4v as it's ferrite.

The amp draw on 7.4v will be roughly the same as 11 1v,

The amps don't change, but the wattage alters on 11.1v,

Watts = Voltage X Amps 

All you are doing is testing the amps on a meter,

without risking smashing the piston at silly speed,

Or excess heat being generated on a high amperage.

Get the amps read from a meter on a 4-5 sec auto burst,

Ensure it is below 20amps on a meter reading.

Is the sector/gun short stroked ???

Coz SP110 spring is near 400fps

Yes you lose a bit on a 300mm barrel,

But think you are losing some FPS somewhere too,

Coz the gun is losing efficiency it is working more,

on the SP110 or M120 spring unless SS'd 2-3 teeth.

And if running inefficiently that 47rps is dubious,

Unless motor is a High Speed one,

Which would explain it a bit along with heat/amps...

A number of things don't quite add up to me,

The slightly higher rof on a higher spring,

Lots of heat & killing batteries etc...

Motors not making much of a difference ???

(They should as you have a range of performance)

Yeah some stuff ain't quite as it seems to me,

So check the amps on a RC power meter/analyser...

Seems like you have used a SHS lightened piston,

so I wonder if the piston is binding quite a bit...

Which would explain some things, heat, amps, some power loss...

Yet this would effect the rps, which is quite high still...

So yeah, some things are not quite adding up to me ???

 

[Piman]

Agreed, check everything is free moving. You have checked the shimming but check the piston and tappet plate are free to move under their own weight when the gearbox is fully tight.

Have you tried backing out the motor just a 1/4 turn?

 

[Iceni]

Iceni, thanks for this on the batteries. gotta be honest and say the calculations have baffled me and i'd love to know how you work this out. Im not for moment questioning you on this, simply stating that i dont understand it and would like to know more. Im curious as to how you work out the ratings.

It's just maths.

C is a unit - Whenever you see C it actually has a value dependant on the battery, It's not just a letter.

C is worked out as the nominal discharge over 1 hour. So for 1450mAh (milliampere hour) you have 1.45A over 1 hour, therefore the value of C is 1.45.

Nominal C is important. It gives you your 1 hour discharge time, but also your safe 1 hour charge time. If you have a battery capable of fast charging a 3rd multiplier for C will be given. Say 5C charge - this  is the charge multiplier - not all batteries have this.

1.45 amps is the safe 1C charge rate over 1 hour. 1.45 x 5 = 7.25 amps is the safe 5C charge rate, Equally you will see a time reduction so you divide 1 hour by the charge multiplier 1/5 (x60 to convert to minutes) = 12 minutes to fully charge.

20C/50C are just multipliers of the nominal C value that show the total discharge the battery can perform. The final value changes depending on capacity.

So a 1.45C 20/50C will be able to supply 1.45 x 20 = 29 amps and 1.45 x 50 = 54 amps.

It's easy to fall into the trap of thinking 10/20C is worse than 20/40 but because that is just a multiplier you have to understand it's dependence capacity to give a meaningful value.

10/20C 2600mah = 26/52 amps    20/40C 1250mAh = 25/50 amps.

In the above instance the 10/20C 2600mAh will run for longer, providing the same amps as the faster looking 20/40C.

Equally you can use the same math to work out the time to discharge. By using division.

You have 1.45Ah and are drawing 35 amps, therefore you can divide 1.45 (1hour) into 35 amps = 0.04 since hours are not decimal you then have to convert to seconds. To convert decimal hours into seconds you multiply by 3600.

1.45/35 = 0.04
0.04 x 3600 = 149 seconds = 2 minute 29 seconds.


And finally the comparative C used in brackets is just a value to express what multiplier your current drain is at. It's an easy way to compare values, but equally if you have already worked out your max amps that works as an equally good comparison tool.

95 amps / 1.45 = 65.5C



Voltage is largely unimportant when you are doing Amp math. Voltage acts to increase the total energy but it doesn't increase the total amperage.

So a 7.4v produces less KWh's than an 11.1v but the amperage is the same. Equally you could express the value in Joules. 11.1v gives more Joules and yes it's the same unit that we express bb energy in.
 

 

[Piman]

Couple of key things here with batteries.

1. LiPos should never be fully discharges so using their full capacity in any calculations is not good. Aim for half to have a long life.

2. The issue is not the wrong battery. Don't just get a bigger battery. You need to find out why you have an excessive current draw.

 

[Caber77]

Really appreciate all the info from Iceni on the batteries and will as a temp resolution get a bigger battery that will provide enough juice.

I'm also in total agreement with Pinman that I need to find the cause of such a high amp draw. Considering everything is new I can only suspect it to be a combination of factors on resistance from gear ratio x spring tension putting stress on the motor. But, I could be completely wrong..

Couple of key things here with batteries.

1. LiPos should never be fully discharges so using their full capacity in any calculations is not good. Aim for half to have a long life.

2. The issue is not the wrong battery. Don't just get a bigger battery. You need to find out why you have an excessive current draw.