Current Limiter

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
S

Soldy

Member
Joined 2017
I didn't measure it, but an educated guess would be 50-60A.

I heard that before, but as long as the current doesn’t exceed the thermistor’s current limit everything should be fine, right?

Just for my understanding: If two 50 Ohm thermistors would be wired in parallel at 230V a current of 9.2 A would flow through the circuit. Let’s say one brakes (for whatever reason): Now only one 50 Ohm thermistor is wired in series → Only 4.6 A would flow.

Just because one resistance value is higher, doesn’t mean that the other one has to let through more current, does it?
 
scottjoplin

scottjoplin

Banned
Joined 2015
The current through the thermistor is limited by it's (cold) resistance. It's Ohm's law. Because it's bypassed by the second relay it doesn't get a chance to get hot, resistors could be used but the thermistor gives another layer of safety if the relay fails, resistors would overheat and explode. This article is a bit heavy going but it's worth reading (and re-reading) Soft-Start Circuit For Power Amps
 
S

Soldy

Member
Joined 2017
Yeah but does it matter? The thermistor with the higher cold resitance would "get" the same current if the other thermistor wasn't there.

So if the designer is aware that a 50 Ohm thermistor could have 60 Ohms due to the tolerance and 230V would suffice to get it hot, then why not.

Or for the other case: if it had 40 Ohms and the current doesn't exceed its limit then it should be fine.

Thx for the link, I'll take a look at it.
 
scottjoplin

scottjoplin

Banned
Joined 2015
Yes the current would be divided according to the resistance, the issue with thermistors in parallel though is that if one has lower resistance than the other it will heat up quicker which would cause it's resistance to fall quicker so the other takes even less current, so imbalance increases. Basically it means thermistors in parallel are a waste of time. Also in this case they aren't going to get hot anyway
 
Last edited:
S

Soldy

Member
Joined 2017
My first semester eleretric class was some time ago, but I thought, that the current of one resistance/thermistor is independet of the other when wired parallel because both resistance/thermistor "experience" the same voltage.
 
Last edited:
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom