How big is yours ? (for long lasting performance)

[Jan_Donadoni]

Obviously I am speaking about batteries (what else?).
I red through the forum trying to find out the "state of the art" of current situation regarding batteries.
That is, generally speaking, german tanks had an estimated endurance of 3 to 5 hours driving full ahead in real world. Longer on paved roads, shorter on rough terrain.
I have not heard of anyone having such an endurance on our tanks.
Personally I need a full night to have the batteries fully charged. Thereafter it takes me more or less 30 minutes to close the tank and drive it into my car. Another 30 to 60 minutes to reach a nice spot to drive around and discharge the tank. All this has to be doubled for going back home and putting the batteries under charge again. Total 3 to 4 hours in preparations. So I would like to have as much fun as possible when finally driving around the tank. A 1:1 ratio (preparations to fun) would be perfect, but I understand it's hard to reach.

So "how BIG is your battery?". That is, higher amperage means "longer performance" (and obviously more fun).
Big batteries also mean "heavy battery", but this (in my opinion) should not be a main problem/issue since we already drive around full metal tanks weighting 100 Kg and up. This means that the largest possible batteries would add 10 to 20 kg depending on model.
The only possible issue is the eventual reduction in up-slope performance.

Example. The Jagdpanther which I recently bought runs on two 20 aH batteries. They need to be replaced since they are aged and one is no longer working well, so I am looking around for good alternatives. Since the Jagd has no turret I can put inside two really "big bad boys" which should also bring forward the center of gravity.
With proper support base I would have total space of approximately 17,5 to 20 cm width ; 45 to 50 cm length and 16 to 17,5 cm height.
This would be sufficient for 50 to 60 aH batteries. From my calculations this should give a performance up to 3 or maybe even 4 hours.
Does anyone have experience with such large batteries? their weight could start to be an issue? Does the weight increase hamper or limit the up-slope performance?

The other tank, the Tiger, has moving turret, so I will not have the opportunity to install such large batteries, since they have to be confined in the rear.

Finally the little ones, like the 222. Here the BIG problem is the "small" space for batteries. I am ending some calculations which should allow me to put (better speaking "press") inside 4 LiFe batteries rated 13,2 x 4100maH each. This would total 8200 maH on 26,4V.
LiFe batteries ar smaller, much lighter than standard Pb batteries, have not self ignition issues and could be charged and balanced in an hour or so. Since my battery charger can load two at a time this would take me 2 -2,5 hours to get back on the road. Anyway there are professional charger-balcancers up to 10 batteries at a time.

Going back to the beginning I could have a "perfect day out" having a first drive with the 222 (still in building phase, but I like to dream), for a fast and deep penetration behind front line for a "scouting mission" (our informers told me that some nasty factory-fresh T-34 are approaching) than put its batteries under charge. After getting in touch with the enemy "ahead with the big guys!" (that is the Tiger or the Jagd) giving the new soviet neighbors a warm or even fire-hot welcome. Finally after the battle a final round trip with the 222 again for "wreckage count" (the general like to send detailed battle reports to OKW).

[John Davie]

Hi Jan,

Batteries is a very subjective issue. I tend to go for the biggest (within reason) that is practical. It is also very dependant on the terrain - 'easy' running on smooth flat surfaces greatly extends the life, whereas hard work in mud, hills etc uses more battery.

For example:
My 222 has 2x4.5aH which are fine and it runs for a long time, I don't know how long because it has always been longer than I needed.
My Comet has 2x33aH and again I don't know yet how long they run as I've never run them down but I know it is more than 1 hour of hard use.
My Sherman has 2x19aH and again it has always run for longer than I need.
My sdkfz7 has 4x7.5aH and runs for about an hour or so whilst towing the 88, which is hard work for it.
I have other stuff, eg a 110kg tank with 2x45aH batteries whic will run for more than 3.5 hours.

Hope that gives you some ideas.

John

[Jan_Donadoni]

Thanks John!
in the meantime I've found something really interesting for the 222. It's a 7 cells LiPo, rated 25,9V for 6,3aH small and just 1,2Kg that is really light compared to standard Pb batteries and also much, much smaller. Finally the price! 80 Euros, more or less, which is pretty a cheap price (LiPos are becoming cheaper every day). I hope this will allow me a greater travel time and also spare some space inside, since I am thinking of adding sound and smoke.
Just one important thing with LiPos is NOT running them too long, since if you run a cell below 2,7V you are going to "kill" it. But technology comes in help of us, so I've found a "LiPo saver" which checking on the balancer connectors interrupts the battery. It can be set at 3 or 2,7V, so you can choose how much "squeeze" your battery without killing it. This is mandatory since Armortek electronics would still operate at a voltage that would damage the battery. So LiPo could be fine for "light items" that you could take back to the car by hand if the battery saver kills the line, or otherwise set it at 3V (you can set it at 2,7V as some kind of "reserve"), so when when the first interruption comes you have a clear signal "drive straight back to the car!" since LiPo stay strong for a long time, but then tend to suddenly fall flat.

[John Davie]

Jan,

Beware of thinking a 222 is 'light'. It is not something you would want to carry very far, it is a good 25kg - you'd be better off with a spare battery in your pocket!!!

John.

[Jan_Donadoni]

I know that the 222 is not light, but at least compared to a tiger, it is.
If a Tiger gets struck in the middle of a field you'll have a lot of fun taking it home. The 222 could be picket up somehow. I made exercise with my two kids (4 and 6 years). As long as I can pick them both up in my arms I'll be able to take the 222 for a short while.
Anyway I'll take some extra-emergency battery for all tanks, I do not want to risk dragging the tiger under the summer sun for hundred of meters just due to a flat battery.
A supplementary LiPo for the 222 and two small 12V 13ah for all the others, just to have the time to drive them into the car.

[Christoffer Ahlfors]

Instead of the biggest batteries that would fit, I chose a different approach with many small batteries instead. It lets me fill every nook and cranny of the interior and to move the center of gravity forward (which I think improves realism), but calls for a lot of wiring.



Cheers,
/Chris

[Christoffer Ahlfors]

Oh, by the way - this does add a lot of weight. At first I was concerned with how the mechanics and electronics would cope with that, but after a lot of testing and running in deep snow this winter I must say that the tank is very robust and the motors and everything so powerful that the extra weight is nothing. The weight does, however, increase slippage in steep inclines in the snow. I imagine the prototype would have its limit too.

Cheers,
/Chris

[phil fitzpatrick]

Hi Christoffer
That looks very neat and tidy,I counted 14 is there any more
and what size are they
Cheers
Phil

[Jan_Donadoni]

Hi Christoffer! really a perfect work!
24V but How many aH??? I believe that you could reach my target of 5 hour running time full ahead!
Such a perfect filling or the inner tank space is astonishing. i was really proud of myself when filing the car with my wife's robes when going on holiday (see under the statement " wasn't it better just to put 4 wheels under the closet, instead filling 4 large suitcases?????") but your work is beyond my imagination!

[Christoffer Ahlfors]

That looks very neat and tidy,I counted 14 is there any more
and what size are they

Tidy because the wiring is not yet in place in this picture - it does make a difference...

There are 31 batteries of 4,5 Ah capacity.

They are old UPS batteries that are replaced on a schedule and I can get them for free. Some have to be discarded right away and the rest probably do not have full capacity. Currently, I have only ten batteries with decent capacity, another ten with some capacity and the rest useless so I have not been able to carry out any running time tests. I use the depleted batteries to test the performance with full weight and it has been fully satisfactory. Running time with these "fifteen" batteries has been 1,5 to two hours in -15C and deep snow. After that, the voltage drops too much when making tight turns in deep snow and it is time to return to base.

Originally, I had still more batteries in but as parts have been added to the tank, I have had to remove some for clearance. The turret ring, for instance, cost four batteries. The forward hatches cost two and they still do not close 100% due to their interior detail fouling a corner of the battery below. Just a matter of getting the file out, but I am not sure which part to get going on?

Cheers,
/Chris