A Chequered Chieftain at #10

[Greg Clement]

Hi John
I follow the Chieftain builds on the forum with great interest, they are very informative and inspirational.
Like a few on here I have lowered the rear deck and modified the opening for the engine bay, no detail works yet, need to finish the Glacis plate first.
Yes I have put in some support for the turret tray but much prefer your solution.

[Richard Goodwin]

No problem putting stuff on the thread Greg; its good to see others posting some stuff on how they do it. Is there a right way? Who knows

Nice level of detail on that dozer box, I did wonder if anyone would add the brackets for the conduit

Keep it coming!

[Richard Goodwin]

It seems ages since my last post for a variety of reasons. Too cold outside now to continue with the stillbrew; will have to wait now until better weather appears.

There's been lots of talk about batteries and regeneration with some clearly entrenched in their positions. From my own perspective, I'd like to take advantage of the benefits of LiFePO4 but have concerns regarding the regen current. There appears to be no measurement data out there wrt regen current to make an informed decision although one could potentially say, its related to the speed of the motor. Many think there isn't any regen current since the tanks don't freewheel because of the gearboxes; they do, it just happens so fast they don't see it and in the meantime, over 1000 current pulses have been applied to the battery.

Looking at a few Safety Data sheets for LiFePO4 batteries indicates the following:
1. Do not connect any other power sources to the battery other than the chargers supplied with the battery pack
2. Do not exceed the maximum charge current of the battery otherwise damage may occur

As far as i am aware, the max charge current of a LiFePO4 battery is 1C...so for a 20Ah battery, that would be 20 Amps. Hear's another interesting paragraph that I found posted on the forum from Armortek back in 2011:

The regenerative braking was introduced with the module based Armortek Speed Controller, about a year ago. This is a digital speed controller and it works by sending pulses of power to the motor. In the gaps between the pulses, it sends the power generated by the motors back to the batteries to recharge them. The standard EMD gearbox is between 60 and 65% efficient, depending upon speed. Because of this about 30% of the battery power is lost when driving and when recharging. The new gearbox is 90 to 95% efficient. This means it both uses less power to drive, and recovers more power to regenerate.

Now Chieftain has two speed controller modules; one for the track motors (Unit A) and one for the turret elevation and traverse (Unit B). Clearly, Unit A has to be capable of handling larger currents. The manufacturers blurb indicates that in both controllers, the regen occurs when the motor slows down. Unit B however, also supplies a regen when in reverse!

Certainly with respect to Unit A, it is feasible that a current larger than 1C could be supplied to the battery but the amplitude of this current is really dependent on the motor speed. There is so much grey here, and very little black and white so to speak.

Until more is known, I believe the best thing to do is to get rid of the regen current if I want to use LiFePO4 batteries so my investment is protected until more is known. Now it is possible to do that on Unit A!

Unit A was opened an all the wiring was removed from the terminals (this facilitates removal of the controller from the bottom of the case) followed by undoing and removing the nuts and bolts holding the controller to the bottom of the case. The controller can then be slid sideways out of the casing. That's the warranty gone

The slot at the RC end was then elongated either end as shown below; anyone know the paint code

Unit A was then reassembled. Elongating the slot allows access to the USB port on the controller and the terminals P1 and P2 to which resistor networks will be connected to (one for each terminal) to allow the regen current to be dissipated as heat: The value of each resistor network is calculated using the lesser of the nominal motor current or 8A!

The USB port will allow access to the advanced Options menu via a software package. This allows us to set up things like battery type, voltage and current limits as to when the controller shuts down as well as enabling the voltage clamping on terminals P1 and P2. It also has a diagnostics tab where real-time data from the controller can be obtained and recorded. That only leaves one thing to do and that is to change the DIP switch Position 3 switch to on (Power Supply). Any regen current from the track motors should now be dissipated through the resistor networks on P1 and P2. Should more information come to light that makes regen more favourable, its a simple matter to reprogram and disconnect the resistor networks.

Unfortunately, unit B isn't as flexible and I don't think that the regen can be shut off. There is no USB port to connect too. That said, it is I believe most unlikely to exceed 1C so could be left as is or replaced with a controller that doesn't have regen. If its left, then DIP switch Position 3 will need to be set to Lithium.

Please note, if you do any of the above, you will invalidate your warranty. I have left certain information out to try and ensure only those competent to do so may undertake this.

Merry Christmas to all

[Stephen White]

Richard hi. Interesting discussion. Not sure if I qualify as "entrenched"! More: reasoned and balanced I hope. (I am very entrenched though on not calling it a "Chiefy", although for some unfathomable and inconsistent reason, "Cent" is perfectly OK. Just like Tankies should never be Tankers, although some are.

I discussed with the supplier of my LiFePO4 module this morning concerns about the potential for regenerative current to damage a battery. Their tech support is getting back to me with a data about how the BMS behaves on identifying an excessive current input. In general terms though, the supplier's view was that the BMS is provided with overcharge protection and regenerative power is not an issue. Now, for a definitive answer, we would need to know the data for the BMS cut-out on overcharge and the data for the peak current the Armortek modules might supply. But this answer is encouraging.

The Tracer supplied charger delivers a maximum of 5A, which is a starting point.

Season's greetings.

Stephen

[Steve Stuart]

As some one who is not expert but wishes to be informed I have been watching this thread with interest. Anything that is posted that adds more information and moves things forward is very welcome.
Rest assured that the unbalanced LiPo posts are likely to produce flare ups, just like the real thing, which can be amusing to watch, but hopefully not too serious!
Steve

[Adrian Harris]

I've just ordered a watty low value resistor so I can monitor the current drain with a digital storage oscilloscope, whilst driving.

That should prove if there are any pulses of current being sent back to the battery

Adrian.

[John Clarke]

Richard,
Nice descriptive debate.
Red box third generation Armortek derived regenerative ESC's,(I believe) now appear to be more complex than most would have thought.
Though no sophisticated programming on the B box, just the usual dip switches.?

Adrian,
I'm not sure if/how the older regenerative silver boxes would react to the LiFePO4 systems these days.
The latest batteries would have been barely been a glint in their eye in 2009.
Would it be possible to do comparisons with the ESC's, silver and red boxes in terms of regenerative output of motor to ESC and how much energy actually gets back to the battery itself.

Stephen,
Using Cent and Chiefy terms, (affectionate terms from me) Sorry, guilty I am.
Still, I'm sure there were quite a few other terms used, some may well have been quite derogatory too.

Good news,

I've found a reasonable match for the red boxes.

Happy Lols Hols

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[Richard Goodwin]

Here's hoping all had a great Christmas.

Many thanks John for the paint colour, looks pretty close to me on the screen! Will get some and try it out.

I was browsing through my Chieftain Motion, Audio, and Recoil Packs manual and in particular, the Useful Information paragraph. One part of it says:

We recommend using 2 x 12V sealed lead acid batteries capable of producing 22Ah and connected in series

I believe the we recommend should be removed since both controllers are set to Lead-Acid and it should be made clear that this motion system is set up for lead acid only.

In the same paragraph, it goes onto say that:

Our motors produce regenerative power to the batteries. Because of the high current we do not recommend using Lithium metal batteries

Now that is an interesting statement, why, because sealed Lead Acid batteries are charged at a maximum of 0.3C yet LiFePO4 can be charged at 1C! So if high regen currents exist, are we damaging our lead acid batteries? Don't know on that one that at the moment but i believe that some have the ability to limit current charge to the maximum permissible. Best to check with the manufacturer on that one though.

Noting that Stephens charger charges at 5A, it charges at 0.25C. Now if I remember correctly, the number of recharge cycles (LiFePO4) is dependant on the level of charging current; the higher the current. the lower the number of recharge cycles.

I'm pretty sure there are lots of forum members that are interested in the battery/regen discussion, just a shame that not many contribute since as a collaborative, we could possibly resolve this problem; regen may affect all battery types!

It would be interesting to hear what Armortek have to say on this matter. The information from Tracer will also be useful as would any measurement data from Adrian. That said, if anyone else can provide some useful information then feel free to jump in!

[Richard Goodwin]

With no information forthcoming, I have decided my own way forward wrt what battery my Chieftain will have and how best to protect it from potential damage. This is my starter for 10 for getting the tank mobile; from there I should be able to do some measurements and expand on my conclusions and adjust if necessary. So what are they?

1. Fit a LiFePO4 24V 20A battery - the benefits of this battery type have been well published on here ie size, weight, capacity and of course, safety. This battery type will benefit Chieftain because there is not a lot of room inside and in addition, it is already, a very heavy model in standard form let alone all the extras being added so its increased capacity will be welcomed. I intend to charge the battery to around 85% capacity to enable room for regeneration current when first started up. Interestingly, having replaced my main battery on my diesel Volvo (which has no regeneration capability as far as I am aware) and reset its BMS (yes it has one), I've noted that it keeps the battery at a max 80% capacity!

2. Regen current from the motors will be dumped into a resistor network and not supplied back to the battery. I am of the belief that high regen currents can occur here and it will take the BMS around 1 second to react. In addition, I also believe that high regen currents applied to the battery albeit for short periods, will affect the longevity of this battery type and size. The motor controller will need to be reprogrammed for LiFePO4 batteries and for the dissipation the regen current iaw manufacturers instructions.

3. Regen current from the Turret controller will remain as is since I think the max current supplied will be around 5 amps but I can't say that for certain; its an estimate. This will allow small top ups of the battery without I believe impacting on the longevity of the battery. It maybe, that the initial starting capacity of the battery may either increase or decrease once measurements have been taken.

Before people start ranting, this is the way I'm going to proceed. I'm not saying its the correct way; only time will tell on that one once I can get some measurement data. Enacting the above will invalidate any Armortek warranty, of that I have no doubt but for me, that has long expired anyway! This is now the time for experimentation which I hope, will protect my very expensive battery from potential damage and shortened life expectancy.

On the subject of the Stillbrew creation, I hope to be back on that soon.

Now lets look forward to honouring our Queen and celebrating her 70 years of service to this proud Nation; I only have around 47 years and it feels a lifetime already

[Adrian Harris]

Unfortunately, try as I might, I couldn't get any usable readings from the models. Mainly because the switching noise of the speed controllers swamped any meaningful readings from the scope.

I could see, when running the Tiger at full speed forwards and then stopping suddenly, there was some regeneration, but nothing which was quantifiable.

Adrian.

[Richard Goodwin]

Adrian,

Many thanks for trying. I will of course conduct my own measurements once I have the thing up and running and will make known the results.
It maybe that the inductance of the resistor is having an impact on the measurement; these will be fast rise pulses. Suggest if you have one either a proper current transformer or if you have the red box controllers, using the software we previously discussed. This has a device monitor button which allows you to view, once connected, such things as motor current, battery supply as well as % regen on the P1 and P2 terminals as well as the ability to record it. Hope that helps?

[Richard Goodwin]

Happy New Year everyone!

It seems like an eternity since I last posted anything on this blog of mine There were various reasons for that including moving home etc but hopefully, will now be able to spend some time on 03EB20.

Headlights appear to be the topic of discussion at the moment. I remember starting mine sometime ago; it was only when i looked through my old photos that I realised it was back in 2020 I had incorporated Phil's mod to the stands and had done the same as John and used glass lenses (2 per headlight) with a piece of clear plastic sandwiched in between which had been scored. The lens assembly was then held together using sticky foil tape which was trimmed such that it didn't show through the front cover.

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For the blacklight (IR), I painted the plastic with matt black not being one for theatrics although it could have something to do with a previous life with aircrew survival kit Anyways, this is where i got to back in 2020...

Obviously, I still have much work to do on them like adding in the leds, the cabling around them and the front face securing screws. As much as I'd like to round the bases off I can't since I no longer have access to a lathe and my router certainly can't do that

On the subject of cabling, I've managed to located some solder braid which can be opened up. I have ordered 2mm and 4mm flattened width. The 2mm can take a wire of between 1-3mm and the 4mm is 3-6mm. If anyone is interested, I'll post a link?

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