Battery Voltage

[Mark Allen]

Im about to set off on building the battery for my KT. An 8s LiFePO is nominally 29.6V. Is this too high for the Armortek modules?

If so will a 7s arrangement with a nominal 25.9V be suitable? Currently looking at 70Ah cells dispersed throughout the hull.

Thoughts?

[Christoffer Ahlfors]

Read this first: viewtopic.php?t=5790
//

[Gian Marco Menozzi]

HI Mark,
I advise against the use of lipo in tanks,
I have been using Lifepo4 for about fifteen years now, they are 8S 22 Ah,
they have a slightly higher voltage than Lead Gel,
but until now with the original second series Armortek regulators (ESC),
I never had problems,
I'm not going to advise you Yes BMS or No BMS, everyone does as they want.
HI
Marco

[Mark Allen]

Oops. My mistake. No LiPO, LiFePO. Thanks for reminding me. I am going to use a BMS for sure. Also telemetry for each cell's voltage. Easy with the FrSky.

Christoffer, thanks for the link. Don't know how I missed that one. And it changes my question, Now the question is: A 7 cell battery or a 6 cell battery? 6 70Ah cells seems like fairly easy to fit in a King Tiger. With great weight comes lots of space...

[Adrian Harris]

They may ultimately start off at 3.7 volts, but there is a very fast drop off to a steady voltage:

This was a test of a 4S LiFePO4 battery from Golf Warehouse at 5 amps until it reached 10 volts.

Adrian.

[Mark Allen]

Thank you Adrian. It sounds as if a 8 cell battery will be fine, since the 29.5V is nominal and looks like it will drop right of to around 26V.

I will make up some dummy cells from scraps of lumber around the place and see how intrusive they are.

[Gerhard Michel]

Hi Mark,

a LiFePO4 cell (LiFe) has a nominal voltage of 3.3 V. Therefore 8 cells should be replaceble against 2 pieces of 12 V lead acid batteries without any problems. Please keep in mind that the absolute charging stop voltage for lead acid is 28.8 V; for 8 LiFe cells it is also 28.8 V. Therefore 8 cells are the right number for replacing a 24 V lead acid battery.

I use LiFes between 20 and 40 Ah for my tanks, depending on their size and weight. My full metal King Tiger (non Armortek, about 160 kgs) can drive up to 4 hours with its 40 Ah cells, depending on the operation conditions.

Please keep in mind that a tank consumes a very different amount of energy depending on its operation conditions. My telemetry says that my King Tiger consumes 4 amps when rolling straight forward on plain ground, but it can use up to 60 amps when tableturning on heavy grounds! Therefore the theoretical time of travel reaches from 30 minutes up to 10 hours! This shows that the real time monitoring of the battery capacity is really necessary. My transmitter shows me at any time the consumed driving capacity; additional I programmed acoustic warning messages into my transmitter if a cell comes near to its discharging stop level. This allows me to spare a BMS, and so I can drive my tank to the car without a general stop of a BMS and without any damage to my LiFes.

[Mark Allen]

Gerhard, Thank you. The confirmation is helpful for sure. I agree that the telemetry of battery use and condition is a requirement. Ive been cadding up conceptual functional/block diagrams for the tank. I will proceed with making some dumb cells and see how good/bad the idea is.

[Stephen White]

Mark, Adrian and I did some work on this. See thread here:

http://www.armortek.co.uk/Forum3b/viewt ... start=1020

Stephen

[Mark Allen]

Stephen, Yes, I have read that thread several times, some great information in there.
I referenced it when setting up my X9D transmitter. No problems learning the inputs, mixes and outputs.

The receiver supports Smart bus telemetry and there is a FrSky module for batteries of to 8 cells. Then you can set all those warnings for individual cell voltages.

[Gerhard Michel]

Hi Mark,

I think it is very helpful not only to show voltage information and warning messages on the receiver's display, but to use additionally acoustic warnings at your transmitter when voltage reaches critical marks. Then you don't have to look permanently at your display to get important informations.

[Mark Allen]

Hi Mark,

I think it is very helpful not only to show voltage information and warning messages on the receiver's display, but to use additionally acoustic warnings at your transmitter when voltage reaches critical marks. Then you don't have to look permanently at your display to get important informations.

Agreed. This however is going to take me sometime on the learning curve. If im understanding my manual(s) correctly these things are one in openTX companion? And put on a SD card to put into the transmitter. My current computer will not run companion and I didn't want to go through the whole new computer thing,but I will have to face that eventually.

[Gerhard Michel]

Hi Mark,

unfortunately I can't help you with openTX, because I'm not familiar with it. My Graupner RC has all these things built in.

[Paul Sparkes]

Hi Mark,

I think it is very helpful not only to show voltage information and warning messages on the receiver's display, but to use additionally acoustic warnings at your transmitter when voltage reaches critical marks. Then you don't have to look permanently at your display to get important informations.

Agreed. This however is going to take me sometime on the learning curve. If im understanding my manual(s) correctly these things are one in openTX companion? And put on a SD card to put into the transmitter. My current computer will not run companion and I didn't want to go through the whole new computer thing,but I will have to face that eventually.

You can do lots of settings and add telemetry from the transmitter itself, somethings are easier with companion, others not.