PF Maximum Voltage

[rkkm]

dont really understand what do u mean about diode heat, 3 batteries will generate in diodes 3 ampere and 2,4 watt, can i reduce it? i want to have 3 batteries fully charged and i want it to be save, safier will be 0,6 or 0,8 v diodes as u said?

and short races mean? When i go outside im driving 10-20 minutes with few rests for model, would that be dangerous?

[MajorAlvega]

A diode conducts electricity but it also generates heat while doing it. Each diode as a drop voltage, the 1N5401 voltage is between 0.6 Volt and 0.8 Volt (it drops more with more current).

So if you use 2 fake bateries with diodes of this type and one shunt (a fake batery without diode) and 3x 14500 batteries @ 4.0 Volt each, you will get 3x4 - 2x 0.7 = 10.6 Volt.

Test it for a minute or two and see if it gets to hot inside the Power Functions box. With normal Power Functions M or L motors it will not.

[rkkm]

but these diodes wont do any damage if i put em into rc unit and drive it for a few minutes connedted to buggy motor?

[Marxpek]

@rkkmI would not advice to use lithium ion batteries (or combinations of different batteries) in your rc unit, that unit has no internal protection in it like battery boxes do, if you fry it, its dead... battery boxes will reset themselves with the thermal resistor built in, the rc unit just burns up when the current gets too high (when you increase the voltage on the motor the current is increased aswell).

The diode solution is one but there is always the risk of melting/burning parts since that is only taking away the voltage from the motors, but the current that the unit has to deliver increases, i wouldn't risk the (15 year old and hard to find) rc unit just to get a bit more power, but that's up to you.

The reason the motors stop on reversing the polarity, probably is because of the thermal resistors in the buggy motors kicking in (they do have them built in), and that should be a warning sign to you, if these protectors were not activated you would have fried your rc unit.

And a 10 minute run is very long for the rc unit under high current, with the Lego speed records that i did, i always had problems after a few minutes with the RC unit (with high quality AA batteries)  when drawing a lot of current, the system heats up fast and has to cool down a few minutes, increasing the power supply won't make this any better, even worse.

I'd say, stick to Lego solutions (AA batteries) to make sure you wont burn up your precious old rc gear..

 

Edited April 30, 2017 by Marxpek

[rkkm]

firstly hey marx, im have builded almost identical vehicle as your on channel with steering with speed record 29 kmh, just other rear wheel. For rc unit i use 2 li ion batteries ( charged 8,4v discharged 7,4 v) so for now nothing can happen, i just want to put third battery and reduce voltage cause charged it would be 12v and i want to reduce it to 10,4 volt, no problem with rc unit - i got 2 of them one bought for testing, i want to put third battery and reduce its voltage with those diodes till motors will stop stopping when reversing rotation direction.

so solution with diodes is dangerous or not? im confused, maybe theres an other way to reduce voltage of those bateries?

 

[Marxpek]

8 minutes ago, MajorAlvega said:

Test it for a minute or two and see if it gets to hot inside the Power Functions box

I don't think this is any use, the battery box will shut down around 800ma while 1 stalled buggy motor will draw 1600 ma roughly, so the batteries inside the the pf battery box will never get the chance to heat up.

the RC unit has no curremt limiter, (and 2 motors connected) so there they will heat up a LOT more.

[Marxpek]

True first: hey @rkkm! welcome here and nice to hear my video got you inspired to build something similar, if you need any help with details (doesn't have a alot ;D)  i would be glad to help out.

You mention 10,4v is no problem with the rc unit, that might be true, i'm not sure actually and i am by no means an electrician or something, 

But increasing voltage is not the only thing you are doing here, you are also increasing the current and that is a silent killer here, you can hardly measure the current flowing (especially when in use/drving) i don't know at what current the rc unit fries itself, but i do know you can fry a unit by hooking up more that 2 motors, so lets say 3 stalled 1600ma @ 9v motors fries the unit (4800ma which is insane and would probably melt your Lego wire connections), and with some math i think at 10.4v 2 stalled motors are close to 3700mah so the real question is, when does the rc unit burn up... i can't awnser that for (for now) sadly.

When you are using the diode-batteries, the current in the rc unit probably will not increase unlike i thought earlier, but you are introducing electrical resistance as well withing the battery setup, dropping the flow of current the batteries can deliver and heating them up, it doesn't feel right to me, but might be worth a try, but i would really keep an eye out, you will have to try to stall both motors (worst case scenario) with batteries the in the rc unit, i would hate to try it myself... 

 

[rkkm]

im kinda confused. Im in germany and i was using still 2 3,7 volt batteries li ion and 3 fake aluminuim batteries, now i have used 6 new super life aklaine batteries and they had better performance and supersonic is faster a lot,  but from maths its weird, 2 li ion fully charged batrteries got 1600 mah and generate 8,4 volt and weight 42 grams, 6 alkain ones generate 9 volts and weight 150 g. its wery weird for me - alkaine generate just a bit more voltage cause 0,6 v and weight 4 times more than li ions... And im thinking what do u think about mixing bateries,. i tried 1 new alkaine and 2 li ions for few seconds, it wont blow or anything and supersonic was faster, im thinking about 2 li ions and 2 nimh, but what do u know aboout mixing bateries>? and can someone explain me why the hell alkaines are soo better? from maths they could be worse, weight 110 gram more and generate just 0,6 v more, i hate non rechargables but if alkaines are best, is there way to recharge them? or are there rechargable batteries alkaines, or nimh 1,5 v? im really confused now, i tried today 1 fully charged li ion at 4,2 v and two 3,6 v low charged and still, super sonic is super fast but i cant drasticly change rotation cause motors stop work for few moments, i had to spot supersonic then change rotation direction... one last thing, anyone know if they are alkaines with better voltage or other batteries with dofferent voltage than 1,2 nimh, 1,5 alkaine, 3,6 and 3,7 li ions?

[rkkm]

i had found Ram batteries too ( alkaine rechargable ones ) are they good? Theyre specifics are: 1,5v 3000 mAh no heavy metals, zm-mn type, heres link to wikipedia :

https://en.wikipedia.org/wiki/Rechargeable_alkaline_battery

 

And i found info that li ions got much less mAh than alkaine ones, and kilo watt hour are less ( 3.90 in alkaine, 2.80 in li ion) do kilo watt hour got much to tell for peformance? are they important? Im really confused why my 3.7 v 800 mah li ions are worse that 6 alkaine ones...

[Marxpek]

@rkkmmah indicates how long they will last, not really important for speed i would say.

What is important is the C value (the maximum discharge rate) you want batteries to be able to deliver enough amps to feed the motors.

If you have a 1800mah lion with a rating of 1C it can deliver 1800ma of current, if you have a 1800mah battery with a 2C rating it will deliver 3600ma maximum,

If you have a 700mah lion @ 1C it's 700ma current max, 700mah @ 2C = 1400ma and so on.

id say 3200ma is what we need for the rc unit at its very maximum..

However the Chinese are masters of cheating with all these numbers (c-rating and mah's) and there are a lot of fake/bad batteries on the market especially the cheap ones.

good lion batteries are way higher than 1C, i think its closer to 10C, but i have no experience with them so not really sure.

So in theory your batteries should be able to deliver enough amps, but if they sold you bad batteries....

 

And here is a quote from the article you posted:

"they have a relatively high internal resistance, making them unsuitable for high discharge current (for example, discharging their full capacity in one hour)."

so don't buy those.

 

Here is the solution to the problem: LiFePO4 3,2v-3,6v 3 cells would be 10,8v max, they have high discharge rates (ofc beware of cheap ones) and they are good for the environment :)

 

Edited April 30, 2017 by Marxpek

[Marxpek]

I found another question i think i can answer in you post (some layout would be better).

You have problem reversing the motors when using the lions and not when using the alkalines, i think this is whats happening:

When you reverse the motors at full speed you are effectively stalling both engines, asking roughly 3200ma (2x stalled buggy motor @1600ma) from the rc unit and thus your batteries.

The rc unit can pass through an unlimited amount of current, so much that it can burn itself up, the 2 buggy motors however, are protected by the thermal resistors (when this electrical component passes more than X amount of current, it breaks the circuit and has to cool down to work again, also found in normal battery boxes), this way the rc unit is protected from burning up.

Your lion batteries CAN provide the full 3200ma to the rc unit and will trip the thermal resistors in the motors when stalled (reversing motors at speed) and your motors will need a break.

Your alkalines CANNOT provide the full 3200ma to the rc unit and thus will never be able to trip the motors thermal resistor, however they are delivering enough for the system to give good results. (stalling motors is never a good idea and should be a rare occasion and with normal driving you should never reach 3200ma so alkalines do fine)

More power, more problems, "better" batteries do not always give better results.. 

Keep in mind that Lego is pretty good at designing things and this was designed for.. standard AA batteries

[mocbuild101]

Eneloop Pro batteries are what I use for my RC unit, they are NI-MH 1.2v and have a high discharge rate (I don't know exactly what though).

And mAh is how long they will last, a 1000 mAh battery discharged at 1A will last 1 hour. Also mAh doesn't add up like voltage, it stays the same.

[rkkm]

Today ill be testing how much better are 6 new alkaines than 2 fully charged li ions, i also still think about using 2 800 mah li ions and 2 800 mah nimhs, what do ya think?

[mocbuild101]

You will probably find that the alkaline batteries are faster, and don't last very long.

Li-ions should be stronger but slower, and last a lot longer.

And NI-MH's will be somewhere in between, and probably last the longest.

[Marxpek]

 

1 hour ago, rkkm said:

i also still think about using 2 800 mah li ions and 2 800 mah nimhs, what do ya think?

Mixing batteries is a bad idea and is never recommended, it will work but, different internal resistances will cause some batteries to heat up more then others, damaging them or making them leak or even worse...

Basically: the NI-MH's will not be able to handle the amps the Lion's provide, the setups is always as strong as the weakest link.

 

[mocbuild101]

9 minutes ago, Marxpek said:

Mixing batteries is a bad idea and is never recommended, it will work but, different internal resistances will cause some batteries to heat up more then others, damaging them or making them leak or even worse...

Yes, I forgot to say that...

 

On 18/04/2017 at 1:14 PM, mocbuild101 said:

Mixing different types of batteries is not recommended.

Actually I did!

 

Edited May 1, 2017 by mocbuild101

[rkkm]

Hmm, i think that on not long runs, 3 li ions generating 12v will be good to beat high speeds, i want to  beat 30 km/h with steering :) i tried it and it dont fry whole rc unit even at 1 minute drive.

still thinking about Ram - rechargable alkaines, but i dont think that they are as good as normal alkaines... Im kinda mad cause i invested much in li ions - 25 euro for lcd charger, and15 euro for 3 aa 800 mah ones, and 15 euro for 4 600 mah aaa ones and 2 li ions are worsee than 6 new alkaine ones.

[rkkm]

I decided to buy 3 lifepo 700 mah 3,3 volt  bateries, at fully cahrged they got 3,6 volt so 10.8 volt total, hope they will be powerfull.

[Marxpek]

I'm afraid you won't break the record with the 12 volt setup, its more likely you will break/burn your gear, but if you want to risk that over a record, i'd say go ahead, but i would advice you to find another way.

Also the current output with that setup will drop to what the NI-MH can deliver, since they are the weakest link here.

 

21 minutes ago, rkkm said:

i tried it and it dont fry whole rc unit even at 1 minute drive

Driving is not an issue, stalling the motors is and it occasionally happens, i once had a small twig stuck in my gear house for example, blocking both motors.

Forget the rechargeable alkalines, they do not have the power output needed and the have a low lifetime (i saw if you drain em they may only last 20 cycles), perhaps they can work in normal batteryboxes, but not for what you want.

I understand you invested in the lion batteries, but i think they can still be useful in normal powerfunction batteryboxes, just not the rc unit..

research batteries, test any type available to you, check the differences, get the maximum expiration dates on them (matters alot in some cases) and yes it costed me a a lot of money in batteries to get the record, especially since i tried to use only "fresh" batteries on attempts.

1 minute ago, rkkm said:

 

I decided to buy 3 lifepo 700 mah 3,3 volt  bateries, at fully cahrged they got 3,6 volt so 10.8 volt total, hope they will be powerfull.

 

good choice, they are powerfull, but be sure you have the correct charger for them, you cannot charge them as lions, you need a charger with a lifepo4 setting.

[rkkm]

I know, now i had to return my li ion charger, but luckly today its 14th day and i had informed seller about return, ill buy li ion + lifepo4 charger. Yeah i know that li ion maybe will be better in PF batbox, i want to try to do what philo show to not have to use all 6 batteries on his website, no with fakes, i want to cut out one side of both aa battery boxes and this grey part cut in down side and try to fit in it two pre cut battery boxes if u know what i mean, i want to use in one 2 li ions, generating 8.4 v for ir reciever, and in other 3 li ions generating 12 v for motors, i got problem with one thing but i think everyone know what it is - money... I need to wait a week till i get money, just bought lifepos and charger, and i had to buy aaa bat box,  and one li ion aaa battery cause i had 4 and need 5, now i need to wait 2 weeks till iget lifepos and ill try them with rc unit, i had to say that in germany where now i am on a little holiday, in Aldi shop there are super life alkaines, super cheap and super powerfull! i tested them with fresh new energizers and only lithium ones were better, but one of those super  life alkaines cost just 0.25 euro so im gonna buy about 40 of them, just 10 euro, btw i used them just for a test - i saw on whitespahes channel that his white superwonic was driving at about 12-13 and max 15 kmh, my just about 10 kmh and lower with 2 li ions fully charged, now i used alkaine ones and its max was 12,7 but not on flat , i need to test it on asphalt.

[Marxpek]

Well, good luck with your speed record attempts! be sure to get your steering right, the smallest twitch in steering will make your car u-turn, roll over, flip or crash at these speeds, i broke about half the parts on the car at least once with crashes, so the money drain doesn't end with batteries alone ;D keep me updated with your progress, i'm very interested! be sure to film your attempts, crashes make good video's ;D 

I was wondering: how are you measuring the speed?

About the batteries: Beware, be safe, but be fast! LiFePO4 will bring what you need (what brand did you get and what C-rating do they have?)

[rkkm]

I dont know about c rating of them, i bought four of soshine 3,2 v 700 mah batteries 14500 ( aa size ). About measuring speed, my grandfather have an, i dont know how to name it but its a little thingy that tells u about how much distance u had driven from restart, max speed, and real time speed shown ( just like in ccar). For now i need to wait till i buy trac tire, now i have only tires from crawler ( my biggest ) and two from motorcycle, same as u used in your, ill do a post here and vid in yt but be patient, its going out in about 1 month, first need to do own project, wait for new batteries 2 weeks, nwait for tire and i need to go back from germany, btw in which city u live? i got about 60 km to netherlands :)

[Marxpek]

I own the same soshine LiFePO4, they are great, about 10C, so no worries there.

But the crawler tire you want to use will not work, they slip on the rims very easily, they don't fit very well, losing a lot of power with that (i tried them, a rubber band in both sides of the rim helps a bit, but makes the tire unbalanced)

The slick motorcycle tires work well, the motorcross tires work, but not that great, they tend to get bigger (by centrifugal forces) under high rpm and are more "bumpy" than the Trac tires, unlike most people think.. , making them unstable.

And i live in the city of Zwolle, let me know if you want to drop by, we could race and make a vid!

[rkkm]

Yeah i know about  crawlwer tires, i watn to buy trac tire, zolle is a bit to far for now, tomorrow going back Poland, but, in holidays i also be in germany for few weeks, and i have about 200 km to zwolle, so maybe we'll race :) My motorcycle tires are from 8051 :)

[rkkm]

Ok, im kinda idiot, but i have to wait for new buggy motors, i had to repair mine cause i was driving in the sand, but i think if i use pressured air, oil, and clear them wih spiritus, they will be ok, but i had to glue one a bit, i had destroyed all of mounts when dissambleing top of motor to clear up gears...

i was driving in the sand and now gears are making voices like crazy...