General > General Technical Chat

Can you get PTC fuse style devices but designed for continuous operation ?

<< < (3/3)

nctnico:

--- Quote from: Psi on April 17, 2022, 10:08:00 am ---I'm in need of a PTC fuse style device, but it will be tripped more often than a periodic fault situation.
The PTC fuse datasheets all seem to say they're not intended for repetitive use.

Can you get PTC style devices intended for continuous operation?
Or does anyone have any tips for derating a PTC fuse so it will be fine in a continuous operation environment?
Anyone know what mechanism causes a PTC to fail from overuse?

--- End quote ---
Primary rule: A fuse is intended to prevent against fire, not to cover up circuit malfunction or act as a current limiter.

So what you need is a current limiter. For low voltages (up to 5V) there are plenty of chips out there (look for load switches) that have overcurrent and overtemperature protection.

For higher voltages you could use a programmable current source like the LT3092.

Psi:

--- Quote from: Zero999 on April 17, 2022, 05:16:38 pm ---Daft question: why not use a circuit breaker? There are types which automatically reset, which no doubt consist of a bimetal strip, next to a current shunt.

https://www.mouser.co.uk/datasheet/2/645/D_1610_ENG-1109200.pdf

--- End quote ---

The use case was quite unusual.
I wanted it to detect the heat from the component next to it and reduce current if it got too hot.

I was in need of a really simple circuit that anyone with some simple instructions could soldered together deadbug on the back of a solar panel in the field to add simple max voltage cutoff to prevent battery overcharge (18V 5W panel and 12V SLA). So I was thinking of just a 5W 14V zener across the panel. However the space available is tiny and burning off 18-14V= 4V @ 350mA as heat in the space available in high ambient heat was going to warp/melt the plastic case.
So I was thinking if I put a PTC in the circuit it could just disconnect the panel if the zener started to get hot. Which would only happen once the battery was full. etc..

However things have changed since yesterday and i'm now looking at other options. About to start a new thread.
Thanks to everyone who responded.

T3sl4co1l:
Just put a LM317 in series with the panel output?  Or LM1117 or LowerDO if you need every volt.  Solar panels don't care if they're being loaded, they can be open-circuited too.

Tim

Psi:

--- Quote from: T3sl4co1l on April 18, 2022, 02:46:04 am ---Just put a LM317 in series with the panel output?  Or LM1117 or LowerDO if you need every volt.  Solar panels don't care if they're being loaded, they can be open-circuited too.

Tim

--- End quote ---

The issue with a typical linear reg is when the panel is producing full power (18V at 350mA) the reg will burn of the excess as heat and that is too much power for this tiny location and ambient temps.

I created a new thread for a prototype circuit to disconnect the panel once the SLA is full
https://www.eevblog.com/forum/chat/simple-voltage-cutoff-schematic-for-solar-charger-any-tips/msg4124638/#msg4124638

Navigation

[0] Message Index

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod