Batteries for a newby

[Richard Goodwin]

I think the benefits of lithium type batteries are well known now. Now I did consider myself purchasing LiFePO4 battery myself some time ago but noted the Armortek warning advising not to use because of the regeneration current so I did a little bit of research and found a Topic on the web about controller burnout and BMS (Battery Management System).

In a nutshell, the author advised that in order to use regen, you would need to use a BMS designed for it and that the cells used would need to be able to withstand the maximum regen current. On top of this, the controller would burn out if the batteries were fully charged because the BMS shuts off and would therefore necessitate the use of an alternative load resistor to protect the controller. Personally, I think this is sufficient warning to stay away form systems using BMS and stick to good old Lead-Acid or Gel batteries. True, they may not last long, but they are a lot more forgiving!

The topic itself was quite old so things may have moved on since, so happy to be corrected?

[Phil Woollard]

All I'm going to add to this discussion is.....very wise words Richard!

[Gerhard Michel]

Hi Richard,

I wonder how extremely high a regen current must be to damage LiFe cells, which can withstand more than 100 amps of charging current. LiFe cells therefore are safe. Okay, a BMS which is not fitted for regen may be damaged. I'm not a friend of BMSs, therefore I have no experience in it. But where should be the occasion in which our tank would cause a bigger regen at all? My tanks use ESCs with braking channel via EMF (electromotive force), where the EMF energy is used to retard the tank by a flyback diode. This prevents a BMS (and the cells too) from backload currents.

[Adrian Harris]

Personally, I don't think these tanks will move fast enough to generate much regen current.

Having said that, I'm going to be wiring in some current/voltage sensors into the motor wiring of the Centurion BARV to see what values are reported and logged to the transmitter. That should show when and if regen current is being generated.

I think the worst case is probably driving down a steep bank or when unloading from a car/van. I did some climb rests with the first Sherman I owned, so it will be interesting to see what angle the Centurion can manage.

Adrian.

[John Clarke]

This discussion comes up at regular intervals and just when I think I'll be joining the 21st century energy sources I consider making a bolt back for 19th century tech.

All this tech talk makes me just want stick with good old faithful.

KISS.

[Gerhard Michel]

Actually I don't believe that Armortek's nearly self-locking spiradrive motors generate a regen current at all. A regen current is only generated when the motor is forced to work by the model itself without a help by the ESC, e.g. at a steep bank or so. Only one of my five models (the Jagdpanther) comes from Armortek; therefore I can only use this model for comparisons here. My other models use very smooth-running spur gears and really cause noteworthy regen currents.

The Jagdpanther stops at EVERY steep grade when it don't get power by the ESC. Therefore it is quite unable to generate regen current, because only free running motors can generate regen currents. I don't know if there is another Armortek tank model which will move at a steep grade without being forced by ESC. Please tell me if there is another Armotek tank which can free run downhill without being forced by its ESC.

Well, my spur gear models can and will run downhill and must be prevented from doing that to avoid unpleasant appearance and possibly damages at unloading from the car. My ESC has a seperate RC channel for braking where the brake intensity can be chosen stepless. This means I may choose the speed the tank comes downhill without moving the drive stick, only by adjusting a downhill speed control knob. The flyback diode in the ESC consumes the desired amount of EMF and this causes the motors to brake the tank less or more. Armortek models don't need such options I mean.

[Stephen White]

I find some of these discussions pretty unhelpful. Half considered stuff garnered from the internet and personal agendas complicate things when, as many have said, what's required is a simple guide for those who don't want to have to do a lot of research. So, in an attempt to achieve KISS, here are four thoughts for the season of goodwill:

- there is a Knowledge Base guide to read on choosing a battery. It has been read 2771 times.
- lead acid is cheap to buy, gives adequate performance for shorter runs and will cost you more in the long term when you have to replace it. You can expect to be able to use about half the battery's capacity before the tank starts to slow down.
- lithium iron phosphate is more expensive to buy but cheaper in the long run. It will give you better performance, particularly longer running periods, is smaller and lighter and lasts much longer. You can use about 90% of the battery capacity before you see any decline in performance. Unless you know what you're doing, it's unwise to use lithium iron phosphate batteries without a BMS. The BMS will protect your batteries and your model.
- regenerative current is an irrelevance.

Happy, inclusive and diverse seasonal holiday greetings/happy Christmas.

[Richard Goodwin]

Having noted the responses above, I believe it would be prudent to open another topic on the subject of regen current and batteries; I have more information that will I believe be useful so Stephen, would you mind opening another thread starting from my initial post on this and include the others after it until the end?

To answer the newbie question, if your lacking in electrical knowledge (no disrespect intended) suggest you stick to Lead Acid/Gel type batteries as recommended by Armortek.

[John Clarke]

I think this is a good shout Richard. The pros and cons are always a good need to know.
And probably a routine update on the latest developments in the ever changing world of smart electrikrey.
I believe Armortek don't recommend lifo4 batteries, but the battery performance far out shines gell batteries which ever way you look at it.
There maybe good reason for this, (not recommended) just like the remapping of the ignition system of car inside the warranty period.
I have no problem with the expense, but would be pretty disappointed trying to push a150kg lump back into the car with a full battery charge on my own because a firmware bit got triggered.
If upgrades are needed let's hear about them.
I suppose if anything did cause a "lights out" on Chieftain.Hopfully in the right place it would be sitting there, Menacing, Looking good and posing.
Gosh that would be realistic

[Stephen White]

John,

I've been unable to double check with Kian today but I recall that the Armortek comment on regenerative power, as it relates to LiFePO4 batteries, dates from Mark Watkins' time and reflected the state of knowledge at the time. Mark was being cautious in the absence of data about the Armortek system, about the effectiveness of BMS and of the tolerance of LiFePO4 batteries to momentary amperage spikes. Since then things have moved on considerably, not least with two further generations of Armortek motion systems and better data. So it would be good to have Armortek review the comment in light of current knowledge and the considerable experience of using the batteries over the last few years. Lead acid was seen as the default back then but things have moved on and other technologies have matured.

If the BMS does cut in to protect the battery, it's a trivial matter to reset. You just need to connect a charging current and within a minute or two, everything is restored.

[Richard Goodwin]

if the BMS does cut in to protect the battery, it's a trivial matter to reset. You just need to connect a charging current and within a minute or two, everything is restored.

Lets hope it decides to shut down in a strategic position next to the car and that you remembered to pack the equipment necessary for the jump start (BMS Reset)! Don't forget to look cool with beer in hand as if nothing has happened and keep fingers crossed that it doesn't occur again Best make sure there is a crate of beer in the back just in case

I would suggest if using LiFePO4 batteries, you could get rid of regen altogether which is surprisingly easy on some controllers. Providing you do it correctly, you will protect the controller remembering also, that some controllers are programmable via separate software! Why use regen to recharge when the battery last for days as is!

It would be interesting to hear Armortek's response to Stephens questions bearing in the mind that when Chieftain was released, they still recommended using Lead/Acid/Gel batteries!

[Gerhard Michel]

Hi Richard,

a funny tale with a serious background, I mean. Indeed a BMS reset needs some charging current, and you have to ensure that this is possible wherever the tank is broken down. If you have a training area like this it's not a funny thing to realise such a reset if you don't have the ignition key for the wheel loader.......

[John Clarke]

John C, Great post, could save me hundreds or cost me Hundreds.

Stephen Great post, in a field. Do I buy a gell battery to power up the inverter (12v to 240vac), to power up the LiFePO4 battery charger, to reset the BMS or buy another 12v LiFePO4 battery?

Richard, Great post I could get drunk.

But seriously

If it were possible to turn off the Regenerative power output and channel it though load resistors (a heater in a Chieftain, luxury ), that could make more sense in the reliability stakes.
I've come across dedicated ESC's that do consider the BMS, but I think the one I have (Red Box) does not have this option.

I'm not sure if the hype of Regenerative power output has got any "legs" where's the stat's.

Yes it can do it, but what percentage are you going to get? where would the decimal point be?

I'm pretty sure it would depend on which model, how much you drive up and down hills, how much you stop, start, reverse.

Getting old, spotting hype comes easy.

I worked in the power industry for sometime, if your "connected" to the National Grid UK, you will get carbon based nonrenewable energy whatever the hype of green energy suppliers say. Fact.

With no data comes no response.

[Richard Goodwin]

Hi Gerhard,

After doing a little further reading (some call it research ), I now understand what you are trying to say below:

Well, my spur gear models can and will run downhill and must be prevented from doing that to avoid unpleasant appearance and possibly damages at unloading from the car. My ESC has a separate RC channel for braking where the brake intensity can be chosen stepless. This means I may choose the speed the tank comes downhill without moving the drive stick, only by adjusting a downhill speed control knob. The flyback diode in the ESC consumes the desired amount of EMF and this causes the motors to brake the tank less or more. Armortek models don't need such options I mean.

Have tried to turn the motors by hand without success but don't have Phil's biceps! (them's long gone ) so I don't think these motors will freewheel even with the Chieftain mass behind it......ok maybe a little but not much

The ESC I've been looking at can either electromagnetically brake motors or it can voltage clamp. The electromagnetic braking is as you say it is and may need a flyback diode. Voltage clamping requires those diodes be replaced with resistor packs which will dissipate any recharge current as heat thereby negating any charging issues that may (and I emphasise may, since its not known for certain) exist when using LiFePO4 batteries. That and a couple of other changes in the ESC setup should allow the use of this battery type without fear...........apart from the occasional BMS hiccup when you hope you've found the key for the wheel loader

I must stress this is my own opinion and you would need to check this out yourself with the ESC being used. If this is the ESC used by Armortek, you will no doubt invalidate any warranty you have if you try and make these changes though because they are setup for Lead Acid

[Gerhard Michel]

Hi Richard,

well, I must say that I conveniently use only such electronics in my tanks I am familiar with. This means Graupner RC equipment, an ESC made by SGS (TVC B100), a Beier sound module, a Benedini amplifier and some seperate electronics for moving the gun and for recoil. My Jagdpanther had no option packs inside when I bought it, and so I bought only the spiradrive motors from Armortek, and for the rest I used my familiar components. Therefore I have no experience in electronic components used by Armortek.