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lentner3

18650 idea

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That holder looks better than the one with the spindly spring contacts, especially since you've beefed it up a bit with that thicker bridging wire. Any bottleneck now is the relatively small contact patch of each cell on the contacts. 

The only comment I have now is what about reverse polarity protection? It looks like someone could easily put the cells in the wrong way around. I'm not familiar with that esc but I've known others to fail immediately upon connecting a battery the wrong way. 

 

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26 minutes ago, rich_f said:

That holder looks better than the one with the spindly spring contacts, especially since you've beefed it up a bit with that thicker bridging wire. Any bottleneck now is the relatively small contact patch of each cell on the contacts. 

The only comment I have now is what about reverse polarity protection? It looks like someone could easily put the cells in the wrong way around. I'm not familiar with that esc but I've known others to fail immediately upon connecting a battery the wrong way. 

 

I’ve taped up the ends of the cells with red tape. But I do also have concerns about that. Obviously 1 cell the wrong way around would be harmless but both I don’t know. If reverse polarity is applied I don’t think anything will happen. Not sure how to test it without frying the esc. If someone can chip in with a data sheet that would help.

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9 hours ago, SupraChrgd82 said:

That looks really sharp!  I’m quite interested in hearing how the system performs.

I’ll post a video eventually. Few more parts to arrive and the main build will begin. I think the key to good performance is finding decent quality cells. These are good Samsung ones but only 2000mah which considering the size is pretty impressive.

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1 hour ago, lentner3 said:

If reverse polarity is applied I don’t think anything will happen.

A post in this thread suggests that reversing the polarity will cause the tble-02s esc to fail, though seemingly repairably. 

I guess you'll have to try to make it as foolproof as you can with markings and colour-coding, which it sounds like you've got covered. 

If you were really worried, you could add reverse polarity protection with a low-resistance p-channel mosfet (instructions can be found online). 

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4 hours ago, rich_f said:

A post in this thread suggests that reversing the polarity will cause the tble-02s esc to fail, though seemingly repairably. 

I guess you'll have to try to make it as foolproof as you can with markings and colour-coding, which it sounds like you've got covered. 

If you were really worried, you could add reverse polarity protection with a low-resistance p-channel mosfet (instructions can be found online). 

Thanks for the heads up. Although I’ve made it pretty clear I really need to make this fool proof. Have you got any links to a mosfet mod. And would this have any limitations regarding the current? 

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3 hours ago, lentner3 said:

Have you got any links to a mosfet mod. And would this have any limitations regarding the current?

Here's one with a pretty clear depiction of how to wire it up and good explanations of how it works. 

Regarding current limitation, you just need to choose one with low drain source resistance and high drain current rating - this is all explained on that page linked above.  A quick search of RS shows you can get them with current ratings over 100 amps and on-resistance in the milliohms. 

I wonder if you could do something simpler to prevent putting the cells in the wrong way though, something like modifying the shape of the battery holder and the cells so they can only fit in one way around. The same would have to be done with the charger too, though. Having said that, if you're happy they will be able to put the cells in the charger the correct way around, then maybe they'll be fine doing the same with the battery holder in the car?

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32 minutes ago, rich_f said:

Here's one with a pretty clear depiction of how to wire it up and good explanations of how it works. 

Regarding current limitation, you just need to choose one with low drain source resistance and high drain current rating - this is all explained on that page linked above.  A quick search of RS shows you can get them with current ratings over 100 amps and on-resistance in the milliohms. 

I wonder if you could do something simpler to prevent putting the cells in the wrong way though, something like modifying the shape of the battery holder and the cells so they can only fit in one way around. The same would have to be done with the charger too, though. Having said that, if you're happy they will be able to put the cells in the charger the correct way around, then maybe they'll be fine doing the same with the battery holder in the car?

The charger has protection so the cells just won’t charge if put in the wrong way.

the idea of modifying the cell and holder is compelling. Similar the the servo leads where they have the tab and corresponding slot on the Reciever. That could be an easier solution. 🤔 certainly easier than modifying the circuit.

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Or can someone tell me which of the cheaper esc’s have reverse polarity protection. I have some 1060’s, tble02s, some of the various older Tamiya ones too I could switch from my shelfers. I’m pretty sure the 1060 doesn’t have protection. 
I have some of these too

https://hobbyking.com/en_us/hobbyking-x-car-45a-brushed-car-esc.html?queryID=7af62165fb9b9337f58511651052154d&objectID=48605&indexName=hbk_live_magento_en_us_products

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In my experience NONE of the above-mentioned ESCs have reverse-polarity protection. I've personally exploded a TEU105BK by plugging in a LiPo backwards. (Yeah, I know...) I wouldn't know of any that have, even top-spec racing ESCs like my Muchmore Fleta doesn't have any protection.

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2 hours ago, GooneyBird said:

In my experience NONE of the above-mentioned ESCs have reverse-polarity protection. I've personally exploded a TEU105BK by plugging in a LiPo backwards. (Yeah, I know...) I wouldn't know of any that have, even top-spec racing ESCs like my Muchmore Fleta doesn't have any protection.

☹️ That doesn’t sound promising 

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Interesting idea... Just thinking on my side to the 18650 usage... What I found is that discharge rate for LiIon is generally about 10C... I have one 2S Li-Ion 1500 mAh pack at home to work with a SW-01 chassis I will mount soon... With a 370 and a current draw of 2A it is a pretty obvious solution. I'm not sure about the current draw of a 540 motor, and I would check that: with my Li-Ion pack with 1500mAh, it may be damaged quite fast if the 540 current draw is over 15A... And I must recognize I have no clue on this (but it may be slightly above  this)...

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I’m planning on gearing it down slightly or using a 35turn brushed motor. Also the cells I’m looking at are rated at 40amps which I suspect will be ample. I’ll look at the current draw and amps once I’ve got the car built. I don’t think the constant  current will be a problem. Much lesser cells are used for high end drills. With bigger voltages and 550 motors. But we will soon find out.

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Not sure about the exact specs of the 540, but I found this rs_540sh.pdf (mabuchi-motor.co.jp)

Idle : 2A, Max Efficiency 13A, Stall : 70A

Add the servo: I measured how much they draw everytime I get one with my Skyrc Prgobox, and they are all between 2A and 3.5A. This should be added to the specs of the motor to have an idea of the overal consumption...

Could you route me to the link to the 40A rated cells? I may be interested by those, as I believe there is some cases where it is easier to consider a small battery than a bigger one...

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1 hour ago, silvertriple said:

Not sure about the exact specs of the 540, but I found this rs_540sh.pdf (mabuchi-motor.co.jp)

Idle : 2A, Max Efficiency 13A, Stall : 70A

Add the servo: I measured how much they draw everytime I get one with my Skyrc Prgobox, and they are all between 2A and 3.5A. This should be added to the specs of the motor to have an idea of the overal consumption...

Could you route me to the link to the 40A rated cells? I may be interested by those, as I believe there is some cases where it is easier to consider a small battery than a bigger one...

https://www.ebay.co.uk/itm/393181284573
project farm has a good video where he tested all the different specs and the older Sony VTC5 came out really well.

these are the newer higher spec version.

seem worth a try for the price.

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4 hours ago, silvertriple said:

That's sound to be a good pick!

On closer inspection of the specs these don’t seem to be all that great. The Samsung 20s 18650 seem a better option.

Which leads me to another question. If I put two pairs in parallel would this allow for twice the discharge current? 

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7 hours ago, lentner3 said:

On closer inspection of the specs these don’t seem to be all that great. The Samsung 20s 18650 seem a better option.

Which leads me to another question. If I put two pairs in parallel would this allow for twice the discharge current? 

Normally yes... But then, it becomes sligtly more complex to avoid mistake by putting them, which I'm not sure it is acceptable on the bullet proof side considering what you are trying to do... See, with my kids, which i'm not confident enough to let them manage Lipo or Lithium based battery, I went back to NiMH with proper connector:

  • no risk of polarity inversion
  • one single dedicated charger for NiMH only with the ad'hoc connector. when the light is red it is charging, when light is green it is charged, and when light is blinking there is an issue : "stop and ask dad"
  • they can charge the NiMH battery after their session, it will be ready for next run. They can forget it in the car, the risk is very limited compared to Lithium based battery (NiMH can go very low voltage without issue).

I kind of like your idea but for other purpose: I like the weight gain allowed by Lipo and other Lithium based components, and my only problem is that there is some kits in which my Lipo sticks are few mm too long for the car so it won't go in it. Your idea would solve it...

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