Endless Startup Cycle.

N

NaxMan

New Member
Hi, im a noob

Trying to build a gps ear tag for my cattle.
The problem is: Load starts up when battery is 3V. Battery drains to 2.9V due to startup of load. Load turns off. Solar panel charges battery to 3V. Load starts up. Battery drains to 2.9V again due to startup of load. Load turns off. This cycle repeats for days on end. What to do?

Ive tried different types of capacitors. Have tried to incorporate a N Channel Mosfet, but i failed. Can anyone please guide me in the right direction.
94mAh 4.5V solar panel(I cannot go bigger because of weight and size.
Solar charger present.
500mAh lithium battery.
Diode on solar panel + to prevent backfeed.
 

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Solution
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You need a low-power circuit with voltage sensor and hysteresis to make that work. I had assumed that you would have a microcontroller running everything.

Can you share your circuit diagram?
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What different capacitors? You show a 0.33uf, which is very small capacitance, that would not help any surge…Try something like 100uf. However, I think the starting voltage is a bit low to start with and a start load will always drop the battery voltage a little due to wiring and battery resistances.
Can you increase the battery voltage a bit?
 
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I'm puzzled by your 3V battery?, Li-Ion are 4.2V, and fully capable of powering a GPRS modem board.

One of my products at work is a long battery life (5 years plus) logger and uses an Inorganic Lithium battery (standard in loggers), these are long shelf life, high capacity, but only able to supply low currents. In order to power a GPRS modem I add a 1F super capacitor in order to provide the high current pulses.
 
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Check your glasses

It's 0.33 FARADS
 
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thank you for the insight. Yes its a .33F cap . SO it seems like i should up the cap? Space are limited though. I was maybe thinking to keep the circuit open until the battery reaches 3.5ish Volts before closing the circuit? I dont know if such a component exists ?
 
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I've had something like this. You have to wait for the battery / capacitor to get to a high enough voltage that the circuit starts up, without any further help from the solar cell before letting it try. You need to go for a higher voltage to get more energy stored.

If you can let it get to 3.3 V and it drops to 3.0 V while starting, that should work.
 
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Agreed, I think this is the best way yes. If the startup phase is passed then the demand for power is much less. Its just that first 30 seconds bump i need. Like you said: "If you can let it get to 3.3 V and it drops to 3.0 V while starting, that should work." How to hold the battery to charge to 3.3V before letting the load get to it?
 
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It appears you have the wrong combination of components. Since the devices cuts out at < 3V you need a battery that operates just above 3V. We know the LiPo or Lithium Ion offers many sizes that satisfy this and operate from 3.8 to 3.0.

If the solar charger can also be adjusted upwards, then it might work without cycling. Normally Li Ion single cell charge CC to 4.2 then CV and must cutoff at 5% of CC to avoid damage then use hysteresis down to 3.6 before charging higher to reduce aging above 4V.

A good AA battery has 10,000 Farads so forget about reducing voltage sag with a "little" 0.3F cap.
 
Last edited:
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You need a low-power circuit with voltage sensor and hysteresis to make that work. I had assumed that you would have a microcontroller running everything.

Can you share your circuit diagram?
 
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Solution
If you use a Li-Ion battery you should never go below 3V. Turn on voltage should be around 3.7V, or higher.
Ideally you should send the last message before the system turns off. That requires you turn it off yourself.

So you will need something detecting the input voltage and activating your circuit when the battery is charged enough.

Another aspect why you reach the brown out (too low voltage for the ICs) is that the capacity at lower voltage is reduced.
 
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sagor1 said:
Ooopps... Right, need new glasses.
His problem is not the cap then, but battery voltage is problably too low to start with, and voltage drop on start is related to battery internal resistance plus whatever wire resistance the device has.
Click to expand...

His battery supply seems too low to start with?.
 
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NaxMan said:
The problem is: Load starts up when battery is 3V. Battery drains to 2.9V due to startup of load.
Click to expand...

It looks like a standard lithium cell behind the blue PCB.

If you are running that near 3V, it is permanently DEAD FLAT!
You must keep that battery near 4V for it to have useful capacity; otherwise it is doing nothing.

If the battery was in the correct range it should work fine.

It looks like that PCB may be a battery charge and protection board, but you are not using the correct connections to it & the protected output (that shuts off when the battery is too low) is bypassed?

Get the battery voltage correct and add a 3.3V low drop out voltage regulator to set the supply to the other electronics at 3.3V, if that is what's needed.
 
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Hi, Yes standard 1S 500mAh lithium battery.

Agreed, the GPS/load is on "auto-on" so as soon as it detects power it will try to boot up on its own, as this is in a enclosed casing and needs to work independently from someone pressing buttons.

That blue "Solar charger" PCB. The load and battery terminals has no separate power distribution. They are connected directly to each other through the PCB (Ive tested this thoroughly). Thats why its soldered that way to save space.

"Get the battery voltage correct and add a 3.3V low drop out voltage regulator to set the supply to the other electronics at 3.3V, if that is what's needed." This is exactly whats needed or even 3.7V is also fine. But I do not know what component to use for this? If possible can you give me part numbers or the module name? Should I use resistors also? Thanks for you help
 
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The "load" is a tracking device with a phone module in it. They are notorious for taking a large amount of power to start up.

You need to have something to stop it trying to start until the voltage is higher. You could either fit some device between it and the battery that leaves the tracking unit disconnected until the voltage is higher, or find some connection on the tracking device that would enable its running, and keep that off until the voltage is higher.
 
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His battery is completely knackered, Li-Ion are destroyed by running them too low - he needs to get a working battery, and ensure it's kept charged, and that everything is shut down when it's not charged enough.
 
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Nigel Goodwin said:
His battery is completely knackered, Li-Ion are destroyed by running them too low - he needs to get a working battery, and ensure it's kept charged, and that everything is shut down when it's not charged enough.
Click to expand...
I have 20 off these batteries. Some full some not. Its exactly the same problem.
Even if i change the battery
 
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Yes, the solution is quite obvious. I just dont know what part/module/component to make this possible. To hold the power to 3.7Vish then only close the circuit.
 
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