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Hi Paul

BMS I think it means battery managment system , or the wife

Derek

> i have no idea what all the BMS info means.

Most of it seems to the values at which the BMS trips for over voltage, under voltage, over current, over temp etc.

Adrian

Paul - you may have discovered a very good solution.

BMS - absolutely essential. No telemetry in the world is going to protect you when the current draw momentarily exceeds the battery’s limits and does damage. Built in BMS is good. Operating without a BMS is unwise if you value the investment you’ve made in the battery.

Current. The issue is not about maximum continuous discharge, which for most LiFEPO4 is probably around 1.5 - 2.5 times capacity (not x4 as suggested above). It’s about the potential damage which would occur if a spike in current draw momentarily exceeds the battery’s limits and there is no BMS to protect it. The data Adrian and I have seen from our telemetry suggests that a figure of around 10-15A is a typical max for our models but I’ve had two instances when the BMS has cut in to protect the battery. My Tracer 24V 20Ah module has a mix continuous of 30A and a momentary limit of 60A for not more than 10mS. My Cent must have exceeded this when the BMS cut off operated. It a nonsense incidentally to suggest you can react to any telemetry in less than 10mS.

Looking at the specs for the Ultramax, the max continuous limit is 50A and the max instantaneous is a staggering 150A for not more than 5mS. That’s pretty good for our needs - as long as there is a BMS, which there is. The BMS data sheet is interesting. It’s for a generic BMS configurable for a whole range of batteries of different configurations. You’d need to know if that’s the BMS in the battery in question and if so what parameters it’s set to.

The other thing which could trigger the BMS is high cell temperatures. It no coincidence that one of the two occasions when my BMS trippped was on a very hot summer’s day. I now have a temp sensor linked to telemetry to monitor battery external temperature.

Hi all,
in my group we have a dozen tanks,
we all have the life and one uses lipo,
soon will replace them with the life that I linked in the other post,
the only one who has had problems is the only one who has the bms integrated,
we had to tow it with another Tank because the voltage was at the limit and the BMS turned off the Tank,
the Lifepo4 for industrial use are quite robust,
I have been using them for 10 years and I am not the only one in my group and I live happy without BMS,
I constantly monitor the voltage and current absorbed through the telemetry,
in normal use my PZIII absorbs 10/15 A Max, if I face a slightly steep climb on the ground I arrive at 30/40 A,
moreover, the bms is not able to balance the cells, it has a balancing current that is too low about 80 / 100mA,
it would take days to balance them,
I had the bms and I eliminated them,
preferring a balanced charge and telemetry .
Soon i will look for a charger with a higher balancing current,
mine has about 800mA / 1A,
one that has at least 2A or 3A, the charging time would be greatly reduced .
Regards
Marco

‘I constantly monitor the voltage….”; the difference between a human and a BMS is that the BMS can react instantly to an instantaneous current draw excedence, sufficiently quickly to protect the battery. A human being cannot. How do you drive the model and “constantly monitor the voltage…” if the human eye is incapable of focussing on two things at the same time?

This issue has nothing to do with charging.

Enough said - to prolong this exchange will only serve to confuse, if it hasn’t already done so. Paul - the Ultramax with BMS looks to be a good choice.

The sense of a telemetry system is NOT to show or even to avoid current spikes of 5 ms or so, of course. This is also not necessary, because no LiFe battery is hurt by a spike in such short ranges, may it be as high as possible. A telemetry monitoring is able to avoid deep discharging of each cell, no more and no less. But this is absolutely sufficient to protect a LiFe battery at normal use in our models. If the current exceeds the necessary limit, it is absolutely sufficient when the circuit breaker does its job (within a second or so), because a real short cut in our models is very unlikely when the wiring is done well. I now use LiFe cells over 10 years in my tanks without a BMS in 4 of my 5 models and without any problems or damaged LiFe cells.

Like the pictures show our models are treated like little tanks, not like toys. My heaviest drive accident resulted in 2 broken suspension arms with jammed drive train at the left side in heavy grounds (and ca 70 meters away from me; therefore not instantly to observe). The totally blocked motor consumed 114 amps short circuit current, till the circuit breaker stopped the model. There were no electrical damages.



E.g. here the specs of a good LiFe cell. You can see that the peak current of this 40 Ah cell is even I10 which means 400 amps; tenth the load, not only forth I marked above.

This is an LYP battery - LiFeYPO4. The addition of Yttrium changes the performance. The max instantaneous figure is good.

For LiFePO4 a BMS is advisable.

I confirm what Gerhard Michel says,
telemetry is not used to avoid current absorption peaks, but to avoid excessive discharge,
these are the characteristics of my batteries:
Nominal voltage 12 V Operating voltage under load is 12.0 V

Capacity 22 AH +/- 5%

Operating voltage max 14.8V - min 11.5V At 80% DOD,> 1500 cycles

Deep discharge voltage 11 V The cells is damaged if voltage drops bellow this level

Maximal charge voltage 15V (or 16 V) The cells is damaged if voltage exceeds this level

Optimal discharge current <10 A 0.5 C

Maximal discharge current <60 A 3 C, continuous for max 15 minutes from full charge

Max peak discharge current <200 A 10 C, maximal 3 seconds in 1 minute

Max peak discharge current <260 A maximal 3 seconds in 1 minute

Optimal charge current <10 A 0.5 C

Maximal charge current <20 A <1 C with battery temperature monitoring

Maximal continuous operating temperature

65 ° C The battery temperature should not increase this level

during charge and discharge

Dimensions 181 x 167 x 77 Millimeters (tolerance +/- 2 mm)

Weight 3.2 kg Kilograms (tolerance +/- 50g)

https://www.lipotech.net/newstore/golf- ... -22ah.html

I strongly doubt to exceed 200 A of absorption which can damage the battery,
these are the batteries we have in most of our tanks,
I also used it to start my sister's car
Regards
Marco

Stephen White wrote: ↑

Tue Mar 29, 2022 7:44 am

This is an LYP battery - LiFeYPO4. The addition of Yttrium changes the performance. The max instantaneous figure is good.

For LiFePO4 a BMS is advisable.

Yes, Yttrium enhances the performance. Therefore thenth the peak current level and not only forth...

For using a BMS it is not important if LiFe or LiYFe is used. A BMS is good for commercial use in real vehicles like planes, bikes, cars and boats, with strongly defined environmental conditions on one side and users on the other side, who are quite inexperienced (and uninterested) under which conditions their vehicle moves. Such cells are combinded by the manufacturer to usual 12 V or 24 V blocks, containing no balancing fittings but a BMS, of course. They are built to replace lead acid batteries without any change of wiring, charging and discharging.

A R/C modeller however (so I hope) has a certain knowledge and interest in controlling his vehicle, and he needs only a few auxiliaries to treat his equipment well. A telemetry monitoring for discharging and a cell-wise balancing with overload protection for charging are enough auxiliaries to treat this equipment well, I mean. Therefore I would never use commercial combined 12 V or 24 V blocks but only 4 or 8 single cells which can be placed and combined in the preferred manner for best using the available space.

I use my telemetry as a simple fuel meter. It is gauged in %, with an Arduino to calculate % from voltage and temperature. Compensating for current would be nice, there are so many enhancements you could delve into!

My telemetry sensor among others shows the extracted capacity from the driving battery. So I always know which capacity remains for driving when the battery was fully charged at starting the game...

Hi Paul

I have also been looking at the Ultramax 24v 36ah Lifepo4 battery for my Tiger 1. The weight at 9Kg is a significant saving over two lead acid 12v batteries but I am concerned about the physical size 260 l, 169 w and 214 high. I am going to make a mock up out of cardboard this morning to see how it would fit in the Tiger as I suspect it is going to be a tight fit especially with the turret motor hanging down. I have also looked at Tracer batteries but the 24v 20A is very expensive at over £600 plus the cost of a charger.

Regards

Gary

Hi Gary,

I had a similar problem with my Jagdtiger due to the long recoil, when the gun is in upward position. Therefore I here used 8 of the the WINA cells, where the 20 Ah cell is only 148 mm high and the 36 Ah cell is 160 mm high. My (BT) Jagdtiger allows to mount the 36 Ah cells.

Hi All

I made the mock up of the Ultramax 24V 36A LiFePO4 battery out of cardboard and took the following photos. There is very little clearance and I although I have not assembled the turret rings and associated parts yet I doubt if there is going to be enough room to have the battery beneath the turret area. I am assuming the best place for any battery is central to the floor of the tank and not at the rear which is the only other place it may fit, again it would be tight and the smoke unit would have to go elsewhere.
I hope the photos help others who are pondering which battery to use.

Regards
Gary

Gary - that's a foul for elevation. The Tracer module is much thinner but as you say, expensive. I don't consider battery position that critical, I've got my LiFePO4 front left beside the driver's position on my Cent and it doesn't adversely affect running. On your Tiger, you might consider moving it backwards into the engine compartment? The smoker can be relocated easily enough.

Incidentally, that goes to show why British tank design has largely avoided torsion bar suspension because of the impact on interior space.