1x24v or 2x12v battery’s and other related q’s

[Paul Sparkes]

I’ve been using 2x12v lead acid arm batteries in my previous tanks. I have 24v which I then use a 24 to12v converter to change power back to 12v for electrical systems that need 12v.

On the Jagdtiger I’m thinking about using a single 24v 36ah Lifepo4 to save space and weight and to give good run time (important).
Is the 24 to 12v converter a good idea or should I think about 2x12v batteries and take the 12v directly from one battery? I ask as I’m not sure the converters give good power output to the car audio amplifiers I’ll probably use.
This is the sort of unit I use https://www.digikey.co.uk/en/products/ ... RgQAvD_BwE

If a 24v Lifepo4 is the way to go can someone recommend a good supplier and charger, I’m new to the Lifepo4 but have been around electronics for many years.

[florian rudolf]

I using this LiFePo04 - Headway as kit to create your own battery.
https://www.i-tecc.de/shop/lifepo4-batt ... ausatz-8s/
For charge you can use any 8S multicherger like this.
https://www.voelkner.de/index.php?mp=pr ... 0Gru%20Sho

Cheers
Florian

[Adrian Harris]

If you look back through the forum, the discussion about batteries has been ongoing for years.

SLA and LiFePO4 each have their pros and cons and there are vocal advocates for both.

I've been using a 15Ah 24V pack in smaller tanks (Sherman & T-34) for 8 years now, without any issues, and have recently bought the parts to make two 20Ah packs for larger models. Most commercial LiFe batteries will come with a suitable charger but if you roll your own from parts then you might have to source one separately. I'm happy charging mine at 5A, though some people use much higher charging currents.

I would avoid cheap LiFe packs from places like Amazon, as they tend to be too good to be true. Some cheap 20Ah packs have turned out to be a much smaller battery surrounded by a load of packing

Adrian.

[Stephen White]

If you do roll your own, make sure you incorporate a valid Battery Management System.

Some of us are using the LiFEPO4 modules from Tracer UK. Note that because of the different discharge curves, you can get comparable performance with an LiFePO4 battery of smaller capacity than the equivalent Lead Acid. I've run my relatively heavy Centurion on a 24V 20ah battery and have never got close to 50% discharge even after a couple of days of running at TankFest. If it were available from Tracer, I'd now settle for a 16ah battery.

If you want more on this debate, as Adrian says, there are a couple of threads here and a comprehensive Knowledge Base Topic on batteries in general.

[Gian Marco Menozzi]

2 of my friends mounted these:
https://www.amazon.it/ECO-WORTHY-Rechar ... 9871V?th=1
one of my friends tested them with Icharge charger and the capacity is real,
one has a King Tiger and the other a Jagdtiger they toured for the 2 days of the Verona fair without problems (about 4 or 5 hours total),
in my Panzer III I have lifepo4 12Volt 22 AH, for about 10 years,
I ride for a very long time (about 7 or 8 hours), usually I don't need to charge them at fairs, I charge them with a modeling charger in balanced mode at 10/12 A
Marco
P.s. with lead-acid batteries from 22 AH it turned for a maximum of 1 hour 1 hour and a half

[Gerhard Michel]

Hi Paul,

it's generally not a good idea to use 2 batteries of 12 V for driving and connect one of them additional to the equipment needing 12 V; independent of using acid or LiFe. The battery with the additional connection to 12 V equipment will discharge earlier. When you then charge both batteries in line at 24 V one of them will be overcharged before the other is fully charged. In this case one has to charge the 2 batteries one after the other, which is rather uncomfortable.

In my first tanks I used a dc-cd converter 24 V to 12 V to supply the 12 V loads like power amplifier (and another one with 24 V to 5 V for the receiver). This worked fine, but needed some additional space. For my last 2 models I used a power amplifier with 24 V power supply; so I needed only a cheap 24 V to 5 V converter for receiver and sound module. I use no other laods using 12 volts. My Beier sound modules work well with 5 volts when no output power is necessary because using a power amp.

All my models run with 24 V LiFe batteries and 20 to 40 Ah, depending on available space. The first battery I bought has a BMS for testing the new technology, the next four batteries have no BMS because my RC equipment and my charger allow a sufficient controlling of the single LiFe cells I used. My charger is a Junsi ICharger 4010 duo, an extremely powerful charger (up to 70 amps), which is comfortable for strong LiPo cells in powerful model airplanes and also a good choice for big LiFe cells in our tanks, but it needs an additional power adapter when used at mains.

[Paul Sparkes]

Thank you for all the comments.

This is the battery I shortlisted but I haven’t seen any reviews https://ultramax.co.uk/catalog/product/ ... egory/556/
It’s a good price and available unlike others.

Tracer don’t seem to do many 24v batteries, maybe stock shortages.

[Stephen White]

Paul, specs look good although I’m not sure I believe a momentary discharge limit of 150A. Most other LiFePO4 I’ve seen are around 40-60A. 36aH is more than enough capacity - you could get away with half that. I’ve searched for any reference to a built in BMS on this battery but not found any reference. Despite the post above, it’s wise to have the protection. I’ve had two instances where particularly heavy demands on the power train have caused my BMS to trip in and save the battery. Both were associated with trying to turn sharply at very low speed on high friction surfaces. Without the BMS, I might have knackered the battery. It’s easily reset by connecting the charger for a very short time.

[Gian Marco Menozzi]

these are the batteries I use:
https://www.i-tecc.de/shop/lifepo4-batt ... e-12v-20ah
I bought them from another seller but they are identical,
I created the connection for balanced charging
in my group we bought them for 5 or 6 Tanks and we are all happy with them,
they are safe and robust,
a friend in particular dumped them well over the limit several times and we always recovered them,
we do not use built-in BMS,
I check them via the radio telemetry.
regards
Marco

[Christoffer Ahlfors]

Paul,
I got myself a step down converter looking just like yours. It was not even capable of delivering half its rated current without shutting down. If you by "power amplifier" mean POWER AMPLIFIER, I strongly suggest you go for a 24V unit. It might be possible to compensate for the lack of oomph with a car audio capacitor, but they are EXPENSIVE and VERY LARGE, so no real gain. Power converters are the way to go for everything else.

Good luck with your project! I think you will love your LiFe batteries and wonder what lead is good for.

[Paul Sparkes]

This battery from Amazon https://www.amazon.co.uk/LiFePO4-Lithi ... r=8-1&th=1

But no reviews and questionable 4 week delivery makes me nervous.

Batteries has to be the biggest single challenge to make decisions on, except camouflage colours.

[Stephen White]

I’d want to know if there is an integrated BMS and what the max instantaneous discharge current is. Those are the two areas which differentiate the cheaper arrays.

TrAcer does do a 24v battery - look under power modules.

[Adrian Harris]

As Stephen says, current supply is an important variable, which is often not mentioned in cheap battery specs.

This is an identical looking battery from AliExpress, for almost half the price:

https://www.aliexpress.com/item/32847382326.html

But, the maximum continuous current draw is only 20A and maximum peak is 30A.

Adrian.

[Gerhard Michel]

My telemetry (available in all my models) says that currents up to 65 amps are possible. May be there is an undiscovered peak, so I make sure to use only battery cells which can deliver 100 amps and more. My batteries are built of 8 single cells each (by myself) to allow the wiring for balancing each cell.

A good LiFe cell allowes a peak current of 4C which means the cell may deliver forth the current of its capacity. So my 40 Ah cells may deliver up to 160 A. A BMS would only limit this current to its max-amp value (a BMS rating 100 amps is rather expensive) and cause trouble when the tank stops in rough grounds without the possibility of using a charging device. Surely the tank doesn't overload its BMS under good conditions like a tank show area with plain and smooth grounds, and a charging device nearby. So in my eyes a BMS is the wrong way to protect a tank model that is driven like a real tank, sorry. If the wiring is in good condition and the ESC is strong enough for high currents then a simple circuit breaker is sufficient to protect the tank and the battery.

These are the conditions I mean. The steel track links were strained very strong, up to 40 millimeters wet sand was between road wheels and track links, 65 amps were consumed by hairpin-turning. If a BMS had stopped, the tank had to be towed manually 50 meters to the car.

[Paul Sparkes]

Ive had some interesting information back from battery masters.

All of our lithium batteries comes with a built in BMS that will constantly monitor the cells for optimal performance and life
All of our lithium batteries are supplied with their own lithium chargers

https://batterymasters.co.uk/pub/media/ ... -v1i20.pdf

https://batterymasters.co.uk/pub/media/ ... ms_tec.pdf

i have no idea what all the BMS info means.