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Re: Best batteries to use for chieftain

Posted: Sun Oct 18, 2020 11:59 am
by Gerhard Michel
Richard Goodwin wrote:
Sat Oct 17, 2020 11:34 pm
Does anyone have any measurement data wrt current draw of the motors on any model?
Hi Richard,

all my models have -among other shown values on my transmitter- a real time current measurement via telemetry (the other transmitted data are e.g. voltages of each LiFe cell, temps of motors and ESC and -important- the consumed capacity of the driving battery). It's rather astonishing which peak values of driving current you can see and under which conditions they occur.

My non-Armortek models are equipped with spur gear motors of either 350 watts or 450 watts, similar to the spiradrives. The power consumption is also similar to Armortek tanks. My Armortek Jagdpanther actually has dead lead acid batteries and is not operational, therefore I will use data of my other models.

Perhaps discussing my so called Pöti (king tiger with Porsche turret) with about 160 kgs and grippy steel track links showing the following data:

- driving ahead at flat and plane ground: 4 amps (for the whole tank!)

- driving ahead at an ascent of perhaps 10 %: 10 amps

- driving a turn: 15 to 35 amps, depending on kind of surface

- table turn in rough grounds: up to 55 amps, which means an overload of 50 % to the motors.

You see that climbing moderate hills is not as power consuming as turning in the plane. The reason is that when driving ahead the tank treads lie immovable on the ground and the roadwheels roll over them, but when cornering each track link is moved across the ground, while the whole weight of the tank bears upon the track. Therefore much more power is needed to move a tank (original and model) through a turn than driving straight ahead. But I was astonished that the difference makes up to 15 times more!

Re: Best batteries to use for chieftain

Posted: Sun Oct 18, 2020 12:14 pm
by Stephen White
Gerhard, that's useful data. Your observation about the power required to turn on resistant ground matches up with my case of the BMS cutting in when I was attempting to turn the Centurion on grass at slow speed on a very hot day. It's probably the worst case for power consumption. More data would be really helpful, particularly from the heavier models and with the latest Armortek motion system. I suspect we'll find that a LiFePO4 with a max momentary limit of 60A is fine.

Re: Best batteries to use for chieftain

Posted: Sun Oct 18, 2020 1:00 pm
by Richard Goodwin
I don't think the max limit will be an issue either however, the time it can be applied is! Looking at the specs for different suppliers indicates diffent times in which this max current can be supplied for. Some are milli seconds whilst others are seconds. Its worth checking!!

Re: Best batteries to use for chieftain

Posted: Sun Oct 18, 2020 7:42 pm
by Adrian Harris
It would be interesting to know the current coming down that ascent.

If it never goes negative then there's no appreciable regeneration occuring.

Adrian.

Re: Best batteries to use for chieftain

Posted: Mon Oct 19, 2020 10:27 am
by Don Gray
Armortek noob and electronics idiot-savant without the savant part here...

Would you say something like this: https://www.batteryspace.com/custom-lif ... a-pcm.aspx

Meet the requirements you have discussed? What specifically should I ask or look for in a LifePo4 pack?

Thank you for any guidance you can provide.

Re: Best batteries to use for chieftain

Posted: Mon Oct 19, 2020 11:16 am
by Manny Leung
For the Chieftain size could be a factor as there is surprisingly little room in the hull (in terms of height) once the motors and speakers are mounted. The batteries have to be laid flat and one have to be wedge right up the front ,you cannot mount them upright unlike a KT . I'm still scratching my head on how Phil Wollard can fit interior details and still managed to shoehorned the batteries into the Chieftain.🤔

Re: Best batteries to use for chieftain

Posted: Mon Oct 19, 2020 12:17 pm
by Stephen White
Don,

The battery you looked at does have a 60A max charge rate but you might want to check under what conditions (momentary and for how long). The protection specs looks like an effective BMS, which is vital. I'm a bit surprised by the figures for life cycle. At 1000, this seems low. My Tracer pack has a 1500 cycle life. Note also our discussion about capacity. You can never have too much capacity but if cost and/or space is an issue, you could probably get away with a lower capacity than 20ah. See the earlier discussion. Something around 12-14 might suffice.

Manny, yes and one of the reasons I like LiFePO4 technology. I've pushed the battery in my Cent right forward into the driver's compartment and there is still room for a driver figure to sit on top. That also helps with centre of gravity.

Re: Best batteries to use for chieftain

Posted: Mon Oct 19, 2020 2:13 pm
by John Clarke
Manny, Phil uses Doctor Who Tardis technology, Its a lot bigger on the inside than the outside. :lol:

Re: Best batteries to use for chieftain

Posted: Tue Oct 20, 2020 5:29 pm
by Don Gray
Stephen White wrote:
Mon Oct 19, 2020 12:17 pm
Don,

The battery you looked at does have a 60A max charge rate but you might want to check under what conditions (momentary and for how long). The protection specs looks like an effective BMS, which is vital. I'm a bit surprised by the figures for life cycle. At 1000, this seems low. My Tracer pack has a 1500 cycle life. Note also our discussion about capacity. You can never have too much capacity but if cost and/or space is an issue, you could probably get away with a lower capacity than 20ah. See the earlier discussion. Something around 12-14 might suffice.

Manny, yes and one of the reasons I like LiFePO4 technology. I've pushed the battery in my Cent right forward into the driver's compartment and there is still room for a driver figure to sit on top. That also helps with centre of gravity.
Stephen,

Thank you very much! After more looking I think I've settled on this one: https://relionbattery.com/products/lithium/rb24v20 which has readily available specs and seems a bit more "buttoned up".

Thanks again for all your help!

Re: Best batteries to use for chieftain

Posted: Tue Oct 20, 2020 6:19 pm
by Stephen White
Don, pleased to be of help. That battery has some very interesting figures. I'm especially interested to see that the peak discharge current of 60A (as you'd expect) but it will tolerate that level for 7.5 secs. That's much more than the milliseconds seen on others. What's more, the BMS only cuts off the power at 170A for 10 milliseconds. That's an enormous margin of safety and ought to reassure anyone dubious about the effectiveness of BMS in protecting LiFePO4 batteries in our likely usage case. Thanks for letting us know.