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Battery driven RB get bricked

Mon Jun 14, 2021 11:53 am

Hello *.*

I have a satellite location, which is only powered by solar (no other current available). Very cloudy or rainy days cause a later voltage decrease below the working voltage.range during the night.
Until now, I have already 2 routerboards bricked at this location in short time (2 month).
hAP lite (powered by USB voltage)
SXT SA5 HP (sticker/label not readable any more)
Why are the RB get into that state?
Can it be, that even the BL is damaged/erased by voltage drop ins.
How can I flash a firmware/booloader back on these dead devices? (Netinstall is not showing anything)
What RB HW is stable or designed to be solar/battery power driven?
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Re: Battery driven RB get bricked

Mon Jun 14, 2021 7:04 pm

Hmm. Strange. RouterOS does write on startup/shutdown, so very frequent reboots will wear out the flash memory. But two months?

I also think that a DC/DC converter can have problems and get damaged with very choppy and unstable supply voltage (the compensation/feedback-loop will break down)
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Re: Battery driven RB get bricked

Mon Jun 14, 2021 9:16 pm

IMO , although most DC powered Mikrotik devices show a voltage range for operation , you should avoid running your Mikrotik at the lowest voltage.
If you are operating at the lowest voltage , then you are border-line of being below the proper voltage and you can create problems.
The Mikrotik will often write to the Flash system. If the Mikrotik is writing something to flash and the voltage drops below operating voltage , then it is possible to corrupt the flash system with garbage.

A Mikrotik that is sending ( transmitting ) WiFi will always require more power ( amps/watts ) than a Mikrotik that is idle. When a Mikrotik is idle and operating at the lowest operating voltage , a WiFi transmit operation can temporarily use more current which can reduce the operating voltage - and if during this time the Mikrotik writes ( and or possibly reads ) flash, the flash can get corrupted because the operating voltage is to low.

I would suggest , two things.
- Don't use PoE ( Power over Ethernet ) to power the Mikrotik - instead use 14 or 12-gauge wire directly to the power connector on your Mikrotik. The larger wire will help reduce voltage loss.
- Consider , instead of running your Mikrotik directly from battery power to instead use battery power to power a voltage regulated DC-to-DC power supply. You might want to consider something like the now discontinued Mikrotik mUPS ( battery backup PoE injector ). You might want to also consider something like an ALGcom 24-Volt DC-UPS.

* The mUPS connects to a 12-Volt external battery and 24-Volt power supply. When there is 24-Volts from the AC power supply , there is 24-Volts to your Mikrotik. When the AC power is removed , the mUPS then outputs about 20 to 21-Volts to your Mikrotik. Note - the mUPS is not very powerful , so only power one device with a mUPS.
** The ALGcom 24-Volt DC-UPS uses an external 24-Volt battery system ( two 12-Volt batteries in series ). When AC power is applied , you get 24 Volts. When AC power is removed , you still get 24-Volts out , until your external batteries drop to somewhere about 21 Volts. The ALGcom power supply will simply just shut off when the battery is to low , which helps protect your equipment from operating at to low of a voltage.

By keeping your supply voltage to your Mikrotik devices regulated above the minimum operating voltage , I suspect you will no longer brick your DC-powered Mikrotik routers.

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Re: Battery driven RB get bricked

Tue Jun 15, 2021 7:52 am

Thanks for the replies!
I have already a DC/DC converter installed for the SXT 5HPnD from >=9V to 24V, but somewhen in the middle of the night the battery runs out of energy and the 24V supply will drop in anyhow.
So the Mikrotik devices do not check the input voltage and have a predictable behavior when the voltage is below the minimum voltage level, they still try to continue working with all side effects? (Example: driving the SXT - having a voltage range of 5-30V - at 4.5V will cause unpredictable behavior, even damage of the device?).
For the proposal to avoid PoE: Neither the SXT nor the hAP lite have a power connector (SXT can be only supplied via PoE, hAP has only a micro-USB power plug).
Question to the system technicians: Does it help when I install a circuit which interrupts the power supply quickly, when the battery reaches a critical voltage level (e.g. 10V), instead of smoothly going down with the voltage (as it is in the current situation)?
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Re: Battery driven RB get bricked

Tue Jun 15, 2021 8:41 am

IMO whenever one runs some device off a battery, it's good thing to install under-voltage cut-off device. Not to protect powered device but to protect battery itself. None of battery chemistries (lead-acid, nickel, lithium) don't like being completely depleted and one has to protect them from getting depleted. If batteries get completely depleted, they might get damaged, specially so if batteries are constructed from a series of cells (e.g. lead-acid battery with nominal voltage of 12V is constructed from 6 basic cells in series) because it easily happens one of cells has a slightly lower capacity and completely depleting the battery means reversing polarity of that cell.

So if you use 12V lead-acid battery as power bank for your 9-24V -> 24V DC-DC converter, you really should use under-voltage protector which cuts off battery when voltage drops below around 10.8V ... which is still fine for the DC-DC converter. The detriment effect on batteries is even worse if you're using two 12V batteries in series (making them 24V battery pack) if you allow them to deplete completely.

Since SXT 5HPnD is rated to take input anything between 5V and 30V, you should actually replace your DC-DC converter with undervoltage protector (unless your battery pack can run with voltages over 30V, in that case you still need DC-DC converter to protect SXT from overvoltage).

I don't think there are many mass-production electronic devices that would include under-voltage protection (or over-voltage protection for that matter) and user/owner has to ensure that power supply works inside rated supply voltage interval at all times.
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Re: Battery driven RB get bricked

Tue Jun 15, 2021 12:28 pm

Yes I agree with the above, it is usually no problem to simply cut the power to the RB750, but to slowly decrease the voltage below the minimum really can trigger issues.
So as recommended, change the circuitry so that when the battery is below some minimum voltage, the load is suddenly cut.
(and make sure it is powered on only when the voltage is above some much higher value, e.g. 10.8v OFF, 12.5v ON. or else it could end up to be blinking OFF-ON-OFF-ON because when you switch off the load at 10.8v the battery voltage will rise a bit)
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Re: Battery driven RB get bricked

Wed Jun 16, 2021 4:45 am

Similar thing happened to me with SXT LTE running on solar/battery. It was a faulty the battery that bricked the device each morning. Netinstall recovery worked.

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