Minimum Logic Battery Voltage

General discussion of using Roboclaw motor controllers
skcolb
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Re: Minimum Logic Battery Voltage

Post by skcolb »

acidtech wrote:
skcolb wrote:To add a little more mystery to this, I borrowed some relatively new RoboClaw 2x7As to test out, and they behave fine with 5V supplied to one of the servo headers.
This could indicate a problem with the older Roboclaw(s) you have. I sugegst you send one in so we can look it over and wire it up the same way you did to deteminer the cause of the error.
Okay, shall I just send it to your address in Temecula on the "Contact Us" page?
marsrover
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Re: Minimum Logic Battery Voltage

Post by marsrover »

acidtech wrote:When you power the board from the middle pin of S1(eg the 5v rail) you must remove the LB/MB jumper, as you did. Then there is no direct connection from the 5v rail to the BEC circuit. However there may be bleed through or inductive coupling which could cause the LB+ pin to float up to 5v(usualyl it doesnt float that high). That is where putting the jumper across the LB+ and ground comes in(it pulls the LB+ pin back to ground so the ADC doesnt see a voltage higher than 3v on it).
There is more than a little bleed through. If I put 5.00 V on the +5 V rail, i.e. middle S1, (LB/MB removed) the voltage on "LB IN +" is 4.48 V. If I put a 220 ohm resistor between "LB IN +" and ground the voltage drops to 4.41 V. This tells me that the impedance on the "LB IN +" is only about 3.5 ohms, and if I short it to ground something will surely burn. The Roboclaw works perfectly in all other respects. Are you absolutely sure that the "LB IN +" is designed to float, and that there isn't some version of the board where it doesn't?
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Basicmicro Support
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Re: Minimum Logic Battery Voltage

Post by Basicmicro Support »

Yes, send it to our contact us address.

Also, yes that is more than a little bleed through. That indicates a direct short between the LB + pin and 5v which is not normal(it indicates the 5v regulator circuit is damaged in some way). Please send that one in along with one of the older Roboclaws and I'll figure out what is going on.
marsrover
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Re: Minimum Logic Battery Voltage

Post by marsrover »

It doesn't look like a short. I can find no problems with the board. The 5 V rail is very stable at 5.00 V regardless of battery voltage (supplied the normal way, i.e. LB IN). The current consumption is 30 mA at 10 V (a little higher at lower voltage). This is a new unit, not used much at all. I probably should send it in, but I'm not sure it's worth the time and effort (I live in Sweden). If you are curious I can make measurements, but I think I'll keep it. Thanks anyway.
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Basicmicro Support
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Re: Minimum Logic Battery Voltage

Post by Basicmicro Support »

Maybe Im not understanding how you have it wired? i thought you were trying to bypass the onboard 5v regulator? If the onboard regulator is outputing 5v then it isnt damaged and I may not have understood exactly what you are trying to do after all.
marsrover
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Re: Minimum Logic Battery Voltage

Post by marsrover »

Yes, I'm trying to bypass the onboard 5v regulator, but that doesn't work due to bleed through to the LB IN + pin. You then claimed that the 5v regulator is broken, but I say it isn't, because if I power the board through LB IN instead of through the +5V rail the regulator works just fine. It wouldn't if there is a short between 5v and LB IN.

Are you sure that the regulator allows feeding 5V directly to its output pin? I've never seen a datasheet for any regulator mentioning this, and it feels like it could lead to "undefined behaviour".
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Re: Minimum Logic Battery Voltage

Post by Basicmicro Support »

With a good unit it should not be a problem. I took several boards and tested this. There was no bleed thorugh. However I have one board that does show bleed through(it was an otherwise damaged RMA that was sent in). it shows about 400ma of current draw when LB+/- are shorted and 5v is supplied from an external supply.

If the board is otherwise working properly then I suspect the damage is not critical in your case. Removing the 5v regulator however would be the only option short of sending the board in.

The regulator output of the 5v regulator is functionally a mosfet and a voltage divider(182k/60k)for feedback to an opamp. If the 183k/62k divider was damaged the 5v would be shorted to ground, not to the LB+ pin. that only leaves the mosfet back to Vin being the path back to LB+. I would guess its damaged on your board but not enough to prevent regulation when you switched back to it. However I would suggest that will probably fail out right eventually since it has been at least partially damaged.

The regulator inputs can be from -20 to 60v. Since the output would be at or near 5v during transients by as much as -20 to +60 on Vin it should not be dameged by 5v on the out pin whil 0v are on the in pin.
marsrover
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Re: Minimum Logic Battery Voltage

Post by marsrover »

In that case it really sounds like I should remove the regulator. I don't want it to fail later. I did this and now I have a green light when I feed regulated 5V to the +5V rail, so I'm happy. I have to say to say it's unusual with products that have support forums as good and as active as this one. Thank you.
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Basicmicro Support
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Re: Minimum Logic Battery Voltage

Post by Basicmicro Support »

We've been doing this with one product line or another for just about 20 years now. I've always found good support helps sales. :)
jorchard
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Re: Minimum Logic Battery Voltage

Post by jorchard »

acidtech wrote:We've been doing this with one product line or another for just about 20 years now. I've always found good support helps sales. :)
After attempting the suggestions on this thread and still have no luck with my boards...let me ask the simplest of questions which were not so obvious in the user manual.

Context: I've a persistent low Logic Battery input error. LED blinks four times (error code as stated in manual).

1. can I connect a 5V supply to LB+/- and also connect the micro USB?
2. the guidance in the manual says to connect a jumper between LB-MB if you don't want to use an external 5V supply. Where is pin MB?
3. the manual states the error can be cleared by resetting the board, but no where in the manual is the reset pin stated. Is reset only possible via software?
4. if 5V is supplied to LB+/- or the micro USB, AND the power to the battery terminals, i.e. +/- is disconnected, should the logic side of the board turn OFF/ON?

Clarification of these questions will go along way for newbies like me, so we don't fry our boards. Nevertheless, thanks for making a viable product!

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