HL 6+ low voltage

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Timbo68
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HL 6+ low voltage

Post by Timbo68 »

I have found that my HL MFU's shut down on low voltage - or so it seems. The tank doesn't simply slow down, but stops and reverts to the standby (lights flashing) state. After a few seconds, it will restart, but shuts down again. I've conducted some tests on different batteries, and found the following...

NiMh 3000 mah start voltage 8.02v, shutdown at 7.16v.
LiIon 1800 mah (as supplied with HL tanks) start voltage 8.19v, shutdown at 7.00v.

Here's the strange thing -
LiPo 2S 70c start voltage 8.4v, but no shutdown. Instead, the LiPo alarm triggers at 6.52v (although set for 3.4v per cell).

Why is there no shutdown of the LiPo, but with the other two? Has anyone else any experience with this? I can't see how the MFU knows or cares what battery is attached, but my knowledge of electronics is strictly limited!
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abramsky
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Re: HL 6+ low voltage

Post by abramsky »

In both my son's tanks with TK 6.0 and 6.1. on board, no matter what battery we use (green stock NiMh 2000mAh and in the second Turnigy 5000mAh 2s LiPo) voltage regulator in both of these MFUs cuts the power around 6-6.5v.

Remember that the absolute value for LiPo is 3v per cell. Exceeding the lower limit of 3v will cause permanent damage to the battery.
Timbo68
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Re: HL 6+ low voltage

Post by Timbo68 »

Interesting - my NiMh batteries don’t get that low before cut off. With my 6kg Tiger, the stock HL LiIon batteries give about 10 minutes running only, so I don’t use them, but a decent NiMh or a LiPo is much better. Why the MFU cuts NiMh off at a higher voltage than for LiPos is a mystery - to me at least...

I have my LiPo alarms set for 3.4v per cell, to prevent any damage - and I keep them in charging bags in a vented metal box.
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abramsky
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Re: HL 6+ low voltage

Post by abramsky »

NiMh batteries have much lower current efficiency than LiPo and LiIon. In NiMh, the voltage drop occurs as soon as the battery is connected to the receiver and the discharge of NiMh batteries with the same capacity as LiPo and LiIon will occur much faster. Lithium batteries, on the other hand, can give back energy much longer under load, and the discharge curve is more flattened, so you can drive almost at the same speed until the battery is discharged.
Caution. An alarm or a module shutting down power below 3V per cell is required. This is the absolute minimum that will kill your battery if exceeded. The safe level is 3.4 - 3.7v per cell.
And one more thing. Voltage measurements are made when the battery is loaded, otherwise it will show you a higher voltage than it can actually give during operation ...
Timbo68
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Re: HL 6+ low voltage

Post by Timbo68 »

Yes - as I mentioned, I have my LiPo alarms set at 3.4v per cell.

I'm still curious at to why the MFU allows LiPo voltage to fall much lower than NiMh before shutting down,
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abramsky
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Re: HL 6+ low voltage

Post by abramsky »

Read my previous post carefully again ...

1. NiMh have lower current efficiency and a very fast voltage drop from the moment of starting with the load (driving your model).

Therefore, the MFU with your NiMh does not turn off around 7v at all, but in fact around 6-6.5v - same as LiPo ...

2. You MUST perform all voltage measurements under load (preferably in real conditions, when the model is driving - I know it is difficult but feasible). Voltage measurements after disconnecting the battery from the receiver (MFU) are distorted / unreliable (especially for NiMh) because this battery will show a higher voltage than it can give under load.

3. Use GOOGLE. Enter "NiMh vs LiPo" and select Image Search. Everything will become clear to you :)

P.s. OKAY. I will add this picture because sometimes it is worth more than 1000 words
C__Data_Users_DefApps_AppData_INTERNETEXPLORER_Temp_Saved Images_untitled(2).png
Source - Google
Jay-Em
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Re: HL 6+ low voltage

Post by Jay-Em »

Added to that: Under heavy load, NiMh and LiIon will ‘dip’ in voltage really quick. When the load eases off, they will regain their voltage for a bit. But usually the voltage cutoff has already shut down the MFU.

It’s the reason I use LiPo in all my tanks. They all got big RS390-size motors that gobble quite a bit of power and can temporary overwhelm NiMh and LiIon. It’s related to the ‘C’ value of the respective batteries. C-value = C X cell capacity. I.E. a 10C 7,4 v pack ( say a 3.5 amp LiIon) can muster a continuous 35 amps tops. Sounds like a lot, but power on big brushed motors can be as much as 15 amps each with 390’s, add the turret motor ( 3amp) the airsoft motor ( another 3- to 5 amps) sound module etc. Etc. It starts adding up quite quickly. And worse in heavy terrain or grass.

The cheapie LiIon 1800 packs You usually get with the tanks can -at best- muster about 8C continuosly with a momentary peak load of about 10C, Leaving roughly only 15 to 20 amp for driving and the gizmo’s. The reason our toys come with rather wheezy 400-size high-wind motors for driving. They’re frugal with the amps. A good quality NiMh, on the other hand gets somewhere around 15C, but won’t give more than that. Enough for most applications, though.

However, a LiPo can muster 25- to 50C with sometimes peakloads of 100c. Quite the difference. The problem ( if You want to call it that) is that LiPo’s are quite a bit more volatile than NiMh and LiIon, and have to be handled with a bit of care. Moreso than NiMh and LiIon ( altough they can blow-up pretty good too, but not as fiery and hot as LiPo) Ànd there is a bit of a risk of blowing-up the stock HL MFU, though the 6.xx series have quite a bit more leeway. They only get cranky when the draw exceeds 40 to 50 amp. Quite the improvement.

On a side-note, it’s only thanks to LiPo’s ( and power hungry -but highly efficient- brushless motors) that going 70- to 80km/h with a 1/10 scale RTR touringcar is rather easy. In the “days of yore” ( when I still actively raced electrics) the kind of speeds that were the sole domain of noisy, smelly nitro’s.
And a bonkers car like the Traxxas XO-1 was completely impossible. An electric 1:8 scale Touringcar hitting 160km/h .. straight from the box?? “inconceivable!!!” Pre LiPo attempts stopped at about 140km/h with 24 NiCads strapped in the chassis.. imagine the weight of thàt thing... :P
Timbo68
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Re: HL 6+ low voltage

Post by Timbo68 »

All good stuff - thanks!
My preference is always for LiPos handled with appropriate care, but I’ve been periodically using some stock NiMh which I had, having effectively binned the HL supplied LiIons as hopeless - worse if using smokers... I’ve been through boats (don’t get the LiPos wet...!), rock crawlers and drones before I got to tanks, so I’ve reasonable stocks of various batteries. I don’t plan to let my 2S (70c) LiPos drop to the MFU cutoff if it’s that low, but will stop when the 3.4v alarm sounds. I’ve always had a concern about overtaxing the MFUs, and I originally had in-line fuses on my motors (which would instantly blow anything less than 15amp) and in the battery lines, but with the higher current capacity of the 6.1s I don’t now. All tanks also now have motor heatsinks and two vented fans to keep things a bit cooler in the hull.
I do have some brushless motors and controllers but I’ve not got round to playing with them, as so far brushed have given everything I need.
Perhaps one of you forum battery aces can explain why there is a cutoff on the HL 6+ MFUs - it seems to be undocumented unless I’m missing something. Useful to protect 2S LiPos perhaps, but maybe there’s another reason.
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abramsky
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Re: HL 6+ low voltage

Post by abramsky »

The constructors at HL simply decided that for the MFU to work properly and to keep the battery healthy, the lower level of the power cut-off point must not exceed 6-6.5v. Note that MFUs can work with various types of batteries and for some of them, eg LiPo, the lower safe limit of the discharge value is 3v per cell. If a higher power cut-off value had been set, some batteries (mainly NiMh) would simply not be able to be ridden because an instantaneous drop in voltage under load (which is normal for any type of battery) would cause it to reach cut-off voltage as soon as you start playing. Just use the alarm as usual and don't worry about it any further. I have been using the Turnigy 5000mAh 20C hard case for almost 3 years and there is absolutely nothing wrong with them. The son's 6kg Abrams easily drives 1h in difficult terrain. Usually, after 60-70 minutes, an alarm set at 3.4 - 3.7 volts / cell is triggered.
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abramsky
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Re: HL 6+ low voltage

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Jay-Em wrote:Added to that: Under heavy load, NiMh and LiIon will ‘dip’ in voltage really quick. When the load eases off, they will regain their voltage for a bit. But usually the voltage cutoff has already shut down the MFU.
Yeah. This is exactly what I wrote above.
Jay-Em wrote: ...However, a LiPo can muster 25- to 50C with sometimes peakloads of 100c. Quite the difference. The problem ( if You want to call it that) is that LiPo’s are quite a bit more volatile than NiMh and LiIon, and have to be handled with a bit of care. Moreso than NiMh and LiIon ( altough they can blow-up pretty good too, but not as fiery and hot as LiPo) Ànd there is a bit of a risk of blowing-up the stock HL MFU, though the 6.xx series have quite a bit more leeway. They only get cranky when the draw exceeds 40 to 50 amp. Quite the improvement.
...
And This is a copy / paste of my post from another thread in this forum:
"...since I have two versions of MFU HL TK 6.0 and 6.1 I decided to add my 5 cents to this interesting conversation.
As I am very curious, I looked at what's inside right after I bought it and I can tell you that my version 6.1 from December 2018 differs only in a few small details from the version 6.0 from October 2018 ;)

Mainly because the ESC circuit of the TK 6.1 uses:
MOSFET 80N03
Maximum Drain-Source Voltage 30V
Continuous Drain Current 80A (25 ° C)
Continuous Drain Current 60A (100 ° C)
Drain Current (pulsed) 320A
Total Power Dissipation - 150W ( at TC = 25 ° C )
Maximum Junction Temperature - 175 ° C

And in the TK 6.0 version:
APM2558N MOSFET
Drain-Source Voltage 25V
Continuous Drain Current 60A (Current limited by bond wire.)
Maximum Power Dissipation:
50W - at TC = 25 ° C
20W - atTC = 100 ° C
Maximum Junction Temperature - 150 ° C

So as you can see the differences are, but both versions should withstand much more than a gentle ride. And these Mosfets can withstand much more than while normal ride. Of course, under certain conditions (especially during unskillful using eg. long-term blockage of the drive and the use of motors with significantly exceeded current consumption), the MFU may be damaged, but before this happens, the wires may not withstand such a high current and a fire may occur in the insulation and as a result, a short circuit in the gearbox power cables. In the worst case, the entire model may burn ...

Below two links to the datasheet of both of them:

80N03 (in TK 6.1)
https://alltransistors.com/mosfet/trans ... stor=23991

APM2558N (in TK 6.0)
https://pdf1.alldatasheet.com/datasheet ... 2558N.html
..."
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