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FiShYmAn
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question - random voltages?

Sun Oct 03, 2010 2:12 am

Hey Guys,

Ive got around 100 411AH and 433AH boards and I have recently convered alot of the sites over to a batterys + 24V PSU solution to implement a kind of half way solar setup, I use morningstar solar regulars to take the PSU feed and charge the batterys, and then run the load off the load on the regulator for the cut off benefits, there is no issues with this and has been running fine for several weeks, one site even took a 2 day powercut and ran off batterys fine until power was restored.

However what im puzzled with is the differences in voltages being reported, I have been using the Health monitor in RouterOS to check the voltages of the boards, and one bus bar at one site might have 3 boards on it and they all have different voltages displayed, about a +/- 3v of the actual voltage reading. I have measured (with volt meter) the voltage accross the battery terminals and the bus bar stips the power is fed from, and also the dc plugs that supply the injectors and these all read 27.2V constant which is the correct standby current for the batterys.

I know loss in cables, etc can occur - but most of these sites only have a 4-5m cat5 cable to the radio box, and that is fed with a mikrotik passive POE adapter, and that doesent answer for the site that has about a 30m run and is showing a much higher reading.

So is there is reason the voltages seem so different on every board? In one case It is currently reporting 29V on a RB411AH and the voltage there is not one volt over 27.2.

Cheers Guys - maybe its just a little bug.
 
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Re: question - random voltages?

Sun Oct 03, 2010 6:38 am

I've always wondered how accurate that reading was.
I'm seeing the opposite, I have a 12V supply and my RB450G is reading 10.8V.

I'm also curious how they measure this. Is it a simple A/D in the micro?
What is the reference voltage and how accurate is the reference?

This could be a simple hardware design error or it could also be a simple software error.

The classic error is rounding the per step increment and then multiplying it by the A/D value to get the result.
The higher the A/D value, the higher the net error.

I'm curious to see how well the ROS value tracks across the range of acceptable input voltage, 6-28VDC.
Is it more accurate on the low end or not?

If I have nothing to do sometime soon, I'll break out my bench supply and make some readings.

How accurate is the temp sensor and where is it on each board that supports it?

Edit: My Fluke measures 12.14V at the DC barrel connector inside the RB450G.
Winbox tells me 10.8V. That's an 11% error.
 
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Re: question - random voltages?

Sat Oct 09, 2010 11:48 pm

We have around 20x RB/333 and RB/433AH out there and we see much the same. It appears to be very hit and miss.

We have measured the input current on the underside of the DC connector and we read near enough to the battery voltage, but the RB health monitor can report as much as 1 - 2v out. This is at 12VDC - on one site we have 3x 433AH and they all read different voltages, and are all incorrect.

Our RB/800's in our NOC are powered at 12VDC and they report 18v! ROS 4.11

We've found that Microstar TS-MPPT-60 work really well as a charge controller & battery monitoring on solar sites :)
 
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Re: question - random voltages?

Sun Oct 10, 2010 7:44 am

So it's a useless feature.

I vote to remove the voltage monitor and invest in decent electrolytic caps!

Besides, I'm not sure what I'd do with the information.
I mean if my supply is 12V and it suddenly drops to 6V, chances are the RB will not be up to report the problem.
"Power's gone ---- OH, wait, I'm dead and can't tell you that."

Deciding what to do when a 12V supply reports 11V, is a little more difficult.
Should I truck roll? Probably not.
 
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Re: question - random voltages?

Sun Oct 10, 2010 2:51 pm

So it's a useless feature.

I vote to remove the voltage monitor and invest in decent electrolytic caps! (snip)
I vote to correct both. It could be the same challenge. If the voltage monitor circuit uses a resistor voltage divider circuit to drop the input voltage to the range of the AD converter, the resistors should be 1%, not the 10% (or 20% if cheap) accuracy type. And it only needs to be the two resistors in the voltage ladder. The rest can usually be 10% without problems.
 
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Re: question - random voltages?

Tue Oct 12, 2010 5:56 pm

I vote to correct both. It could be the same challenge. If the voltage monitor circuit uses a resistor voltage divider circuit to drop the input voltage to the range of the AD converter, the resistors should be 1%, not the 10% (or 20% if cheap) accuracy type. And it only needs to be the two resistors in the voltage ladder. The rest can usually be 10% without problems.
If it is the same challenge, then it is a challenge of design skill. It would be quite concerning if 10% resistors were used unless there were a calibration routine. Assuming stability over temperature, resistor tolerance errors can be easily cal'd out.

More concerning might be the A/D reference. Is it internal or external? How is it generated?

I'd like to see a schematic!
 
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Re: question - random voltages?

Tue Oct 12, 2010 7:11 pm

If the reference voltage is not set by a zener diode or other stable voltage controller, either internal or external, shame on them. A 10% resistor supplying current to a regulator like that should not be a problem as a reference.

ADD: And easily adjustable if you wish. Corrected value ends up in a variable "voltage".
http://forum.mikrotik.com/viewtopic.php?f=9&t=44924
 
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Re: question - random voltages?

Wed Oct 13, 2010 12:12 am

A zener is not precise and would require a calibration.
There are precision reference devices specifically for this purpose.

Also, the simple ratio shown in the other post may not work. After all y = mx + b.

If b is non-zero it needs to be accounted for.
 
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Re: question - random voltages?

Wed Oct 13, 2010 2:10 am

A zener is not precise and would require a calibration.
There are precision reference devices specifically for this purpose.

Also, the simple ratio shown in the other post may not work. After all y = mx + b.

If b is non-zero it needs to be accounted for.
That would be ratio plus offset. The last post in that thread.
 
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Re: question - random voltages?

Wed Oct 13, 2010 9:22 am

Oops, missed that.

I think we need someone at MT hardware to confirm if:

[What MT Reports] = ( [Gain] * [Actual Voltage] ) + Offset

Where Gain is a constant and Offset is a constant.

then:
[Actual Voltage] = ( [What MT Reports] - Offset ) / Gain

It does seem odd the voltage measurement is off by so much.

Anyone in the MT hardware department care to comment why? Your input may help us perfect a formula and calibration script.

The actual value is important in solar and battery powered applications.
 
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Re: question - random voltages?

Wed Oct 13, 2010 11:13 am

The voltage monitor on our RouterBOARD devices is giving you only approximate values. If you need accurate measurement for important purposes, use special tester device instead.
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Re: question - random voltages?

Wed Oct 13, 2010 12:30 pm

Or you could build better RB's? I mean take any decent motherboard and multimeter and compare BIOS rail voltages to the readings, They are +/- 0.05 volts almost always

We have 2 RB433AH's powered off the same battery showing 0.8 difference between the 2 boards and even at best thats 1v different from the actual readings.

If you cant include accurate reporting why even bother including it?? Its a real PITA to have to up spec a solar site to handle monitoring gear when the RB's could do it quite simply
 
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Re: question - random voltages?

Wed Oct 13, 2010 1:08 pm

I thought routerboards were for routing :) ?
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Re: question - random voltages?

Wed Oct 13, 2010 1:17 pm

We're back to this? :P Juniper's give you 2 decimal places on their voltage showing the 1.5v, 3.3v, 5v and 12v rails they use.

I'm sure cisco's they same but I haven't personally seen it. A good network operator will be monitoring these and have pager triggers for them. A better operator will have a separate device upstream from the RB and use this to confirm this or pinpoint faults.

Whats the point of including voltage monitoring in RB if it reports are waaay off and vary from board to board? I mean we know the board has power which is about all a false voltage report tells us

edit:// You dont have voltage monitoring on all RB's so why not spend the extra cash on the ones that do and put in a better monitoring circuit

False voltage reading serve no purpose I can think of at all
Last edited by charliebrown on Wed Oct 13, 2010 1:19 pm, edited 1 time in total.
 
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Re: question - random voltages?

Wed Oct 13, 2010 1:18 pm

You can easily tell apart 12, 18, 24 and 48. that's the basic functionality needed for a routerboard. costs would increase if we would make more fancy stuff. I guess you don't want the other feature of Juniper (price).
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Re: question - random voltages?

Wed Oct 13, 2010 1:23 pm

You can easily tell apart 12, 18, 24 and 48. that's the basic functionality needed for a routerboard. costs would increase if we would make more fancy stuff. I guess you don't want the other feature of Juniper (price).
Then why does the voltage show in tenths of a volt? That was a waste of time and programming. I need a voltage on the input. So you feel that 9 volts is ok as an input, as long as the voltage reading show 10.5 volts?
 
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Re: question - random voltages?

Wed Oct 13, 2010 1:24 pm

I will find out the actual precision of this and will post back here.
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Re: question - random voltages?

Wed Oct 13, 2010 1:27 pm

Seriously? The voltage "area" is your answer? If you have to log into a router to tell you what voltage the PSU is then you need to step away from the router and send it back.

And if price is the "issue" then slap another letter on the end of the RB names and charge $10 more for it. Its not exactly rocket science.

I'd pay juniper prices to MT if MT came out with juniper grade hardware and software. Just like i'd shift to Juniper if they came out with a wireless product or series that competes with MT's stuff
 
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Re: question - random voltages?

Wed Oct 13, 2010 1:30 pm

(snip) And if price is the "issue" then slap another letter on the end of the RB names and charge $10 more for it. Its not exactly rocket science. (snip)
There you go, chariebrown! I'd pay that!
 
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Re: question - random voltages?

Wed Oct 13, 2010 1:31 pm

I will find out the actual precision of this and will post back here.
Precision is not a word I would use in this thread :P I think its pretty clear from the posts here that RB's often dont report anywhere near the correct voltage (No 1-2v out is not acceptable)

Here's an easy way out for MT, in 4.12 and 5.0rc2 change the label next to voltage to say Approx Voltage and only show 12v rather than 12.2v
 
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Re: question - random voltages?

Wed Oct 13, 2010 1:39 pm

In recent RouterOS versions, we have changed the formula of calculation, and it's more precise (in v4.11 exactly), as each device has it's own components, in the mentioned version we now use different calculation system for each routerboard model specifically. you will see improvement from say v4.9 to v4.11
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Re: question - random voltages?

Wed Oct 13, 2010 1:43 pm

How much more precise? Do you know what tolerance resistors they are using?

BTW, I just went to Digi-Key and checked 1% resistors. A Panasonic 4.7k 1% SMD resistor is $0.06 each in quantities of one. That would be 12 cents to use those on that circuit.
 
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Re: question - random voltages?

Wed Oct 13, 2010 1:57 pm

In recent RouterOS versions, we have changed the formula of calculation, and it's more precise (in v4.11 exactly), as each device has it's own components, in the mentioned version we now use different calculation system for each routerboard model specifically. you will see improvement from say v4.9 to v4.11
Can you give us some numbers? I.e you were seeing upto 20% different between read and actual voltage in 4.9 and only 6% with 4.11?

Also going to start another thread about changelog's
 
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Re: question - random voltages?

Wed Oct 13, 2010 2:00 pm

Also going to start another thread about changelog's
please don't, there is already too many of them :)
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Re: question - random voltages?

Wed Oct 13, 2010 2:08 pm

Also going to start another thread about changelog's
please don't, there is already too many of them :)

Opps too late http://forum.mikrotik.com/viewtopic.php?f=2&t=45792

If theres too many of them perhaps you should take note and look at the changelogs and release notes attached to other networking vendors
 
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Re: question - random voltages?

Wed Oct 13, 2010 2:09 pm

We are working to improve the voltage accuracy in our new products and will have different design to determine this value.
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Re: question - random voltages?

Wed Oct 13, 2010 2:12 pm

Heh, You could have said that 6 posts ago. Here's a nice goal that would help us alot, accurate down to one decimal point
 
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Re: question - random voltages?

Wed Oct 13, 2010 2:19 pm

You asked why the voltage is different, I explained. Of course we always try to make our products better.
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Re: question - random voltages?

Wed Oct 13, 2010 2:23 pm

Thanks, normis. :D I know you will do your best. You always have! I am not trying to run down MT or Routerboard. I just want to use the best product on the market for the money. That voltage monitor feature is important to me, enough to pay $149 for a RB433AH when a $99 RB433 would do on performance.
 
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Re: question - random voltages?

Tue Nov 23, 2010 12:03 pm

Well for those who look back at this thread,


Nice Job MT!

We got the RB493G in today and chucked it on a 18v PSU and voltage is reporting accurate to .1v measured, We're finally happy to have accurate voltage reporting on remote systems!

As we say downunder: That man deserves a DB!
 
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Re: question - random voltages?

Sun Dec 12, 2010 7:53 pm

RB433AH powered 13,8V - showing 28V. MT 4.13 firmware 2.28. So - where is "improvement"??
 
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Re: question - random voltages?

Mon Dec 13, 2010 2:18 pm

That is a V4.13 bug. Mine show 28v on a router that was correct until the upgrade. :(
ADD: Upgraded to V4.14, and now it is working again! :D

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