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Author Topic: Rectifier Diode?  (Read 609 times)

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Offline gerardTopic starter

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Rectifier Diode?
« on: January 13, 2012, 09:25:31 AM »
hello everybody!

this is my firs time posting on this forum, and i had a question about a rectifier diode

i have built a tracked rc robot using the sabertooth x25 dual esc

right now im using two modified servos, but i am planning on building a bigger one using two AME 218 series gearmotors
they have 18nm of torque and a max draw of 21.3 amps

i have heard that if i connect the battery backwards to this esc, it will totally fry it
will a 30 amp rectifier diode only allow current one way to protect from reverse voltage?
does it have anything to do with the amp draw from the motors?

thanks

ill post a topic about the tracked vehicle soon

Offline Billy

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Re: Rectifier Diode?
« Reply #1 on: January 13, 2012, 02:47:42 PM »
i have heard that if i connect the battery backwards to this esc, it will totally fry it
will a 30 amp rectifier diode only allow current one way to protect from reverse voltage?

Diode will save the circuit from hooking the battery up backwards...it will also kill the driver the first time you try to stop the robot from speed...go back and read the documentation. If it's not clear after that read, come back and I'll explain the rest.

Offline gerardTopic starter

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Re: Rectifier Diode?
« Reply #2 on: January 14, 2012, 08:34:38 PM »
it will affect the esc?
i thought it just blocked the reverse current flow

if it wont work for me, what other options do i have to prevent it?

Offline Soeren

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Re: Rectifier Diode?
« Reply #3 on: January 14, 2012, 11:28:15 PM »
Hi,

it will affect the esc?
i thought it just blocked the reverse current flow
I guess it was a hint towards the current regeneration scheme, but nobody can really say if it will hurt anything (apart from not getting regen. of course, but this loss is fairly negligible anyway if you go more than you brake), unless they have the schematic and some measurements to back it up.
However, there's other reasons for not just plugging a diode in series with the battery, like the voltage drop of the diode and the price if you wanna minimize that drop.


if it wont work for me, what other options do i have to prevent it?
The obvious one: Use a polarized connector and stay on your toes while you mount it to the battery and the Sabretooth - then never remove the wires.
Use a similar (correctly polarized!) connector on the charger.


Another option would be a fuse in the positive line and a reverse biased 40+A diode to blow the fuse if reverse polarized, or (perhaps cheaper and certainly faster reacting per $$) a 40+A SCR controlled by a small diode (eg. 1N4148) and a resistor.

Here's how it would look with a 40A diode...
Code: [Select]
(B+)---[Fuse 40AT]---+---(+S X25)
                    _|_
                    /_\
                     |
(B-)-----------------+---(-S X25)
If the battery's reversed, the diode will conduct (keeping the voltage down to around -1V to -1.5V until the (much slower) fuse is blown.

The insertion drop is just that of the fuse and you need a fuse anyway, so you just add a diode (or SCR, small diode and resistor) and get no further voltage drops.


Quite amazing that they haven't incorporated some protection themselves, instead of just writing a warning in the manual and wiping it off on the customer - at that price and considering how easy it is to bolster it against reverse voltages, something that is bound to happen every now and then among their customers, it sounds a little less than professional... But hey, each unit broken this way may generate a new sale :(
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline gerardTopic starter

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Re: Rectifier Diode?
« Reply #4 on: January 15, 2012, 10:35:37 AM »
thanks so much!

i had totally forgotten about the regeneration feature on the sabertooth

i guess for now ill just use a polarized battery connector and make sure its soldered on correctly

thank you! :)

 


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