Minimum Logic Battery Voltage

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

Post by skcolb » Mon Oct 19, 2015 5:54 pm

On the RoboClaw 2x5A, is there any way to lower the minimum logic battery voltage below 5.5V? It seems that IonMotion won't let me set it any lower (whenever I try to set it lower, it always reads back as 5.5V).

I designed my system to supply switched 5V to the logic battery input. I think we were doing this on some older RoboClaws and it worked, but I see that in the user manual it lists 6V as a minimum voltage input.

Or is there a way to make the controller ignore the logic battery voltage low error? Thanks.

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Basicmicro Support
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Re: Minimum Logic Battery Voltage

Post by Basicmicro Support » Tue Oct 27, 2015 10:28 am

No. 5.5v is minimum logic power because the 5v bec requires atleast that much to produce the 5v rail. However if you supply regulated 5v to the 5v rail and disconnect the Logic battery jumper that should bypass the 5v BEC on the roboclaw. But that 5v you supply must be regulated.

skcolb
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Re: Minimum Logic Battery Voltage

Post by skcolb » Wed Nov 04, 2015 10:31 am

Thanks for the response. I moved the switched regulated 5V power to one of the unused RC connectors and now it works fine, no more low logic battery error.

skcolb
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Re: Minimum Logic Battery Voltage

Post by skcolb » Wed Nov 04, 2015 1:09 pm

I spoke a little too soon. I went to go change around another RoboClaw 2x5A to put regulated 5V onto a servo header, and it would still complain about a low logic battery error. I have a spare so I pulled that out and tried the same setup, and it does not give a low logic battery error.

All of these RoboClaw 2x5A are marked as V5 hardware, running version 4.1.14 firmware. However there's a subtle difference in the style of 0.1" headers between the ones that have the low logic battery error and don't.

Any ideas? For now I can run with the ones that don't throw an error, but curious about the ones that do.

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Re: Minimum Logic Battery Voltage

Post by Basicmicro Support » Mon Nov 09, 2015 10:24 am

Depending when we order headers they can be slighly different. There are a couple different manufacturers we use. But they should have no effect on the voltage rading. However there are errors in the voltage divider resistor resistances. All resistors have some varience.

But I dont think that has anything to do with your problem. Im assuming you have Main battery wired, the LB/MB jumper removed and 5v on one of the servo headers. This leaves the input voltage to the onboard BEC floating. If that input pin floats high enough Roboclaw will start to read its value. We ignore that voltage as long as it is below 3v. But if it floats above that and is read you can get a logic battery error even though nothing is attached to the logic power input. You should be able to fix that by pulling the LB+ pin to ground. A weak pulldown(10k to 56k) should work. Try that and see if that stops the error from happening.

marsrover
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Re: Minimum Logic Battery Voltage

Post by marsrover » Sun Jul 03, 2016 11:08 am

It seems that this trick doesn't work. I have a Roboclaw 2x15A V5. If I put regulated 5 V on the middle S1 pin (LB/MB jumper removed) the LB IN + pin will not float. Instead it will be close to 5 V and there is no way I can pull it low. Is there maybe a trace somewhere I can cut to disable the BEC voltage measurement? I don't have 6 V and creating it would require some annoying redesign. I also don't care about my warranty. :)

skcolb
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Re: Minimum Logic Battery Voltage

Post by skcolb » Wed Jul 13, 2016 2:08 pm

Reviving an old topic here with the same issue. Last time I just ended up using the RoboClaws that did not give the low battery error, but now I only have ones that do show the error.

The setup is the same as before, only running 4.1.16 firmware now. I tried a pulldown resistor on the LB+ pin to ground, first 39K, then all the way down to 1K, but I still get the 4 error LED blinks indicating low logic battery voltage.

FYI, I also tried some newer QA firmware (4.1.19) since I saw some of the ADC stuff was changed, but still get the same error.

skcolb
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Re: Minimum Logic Battery Voltage

Post by skcolb » Wed Jul 13, 2016 4:20 pm

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.

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Re: Minimum Logic Battery Voltage

Post by Basicmicro Support » Fri Jul 15, 2016 9:10 am

marsrover wrote:It seems that this trick doesn't work. I have a Roboclaw 2x15A V5. If I put regulated 5 V on the middle S1 pin (LB/MB jumper removed) the LB IN + pin will not float. Instead it will be close to 5 V and there is no way I can pull it low. Is there maybe a trace somewhere I can cut to disable the BEC voltage measurement? I don't have 6 V and creating it would require some annoying redesign. I also don't care about my warranty. :)
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).

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Re: Minimum Logic Battery Voltage

Post by Basicmicro Support » Fri Jul 15, 2016 9:10 am

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.

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