AC circuit breaker on DC circuit? - Page 1
Forum section: electronics / projects

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: March 06, 2018, 07:41:31 pm
content: I want to add a circuit breaker instead of a flismy switch to kick start my 48V induction heater and was wondering if a 25A AC circuit breaker would do the trick or does it have to be rated for DC current?I am currently using a 25 A AC circuit breaker and it wont open the circuit before there's around 35 A going through it and it get really hot after continuous use (100C or so) on a point of the breaker.What would be the ideal breaker for my requirements?

author: PartialDischarge
author_rank: Super Contributor
timestamp: March 06, 2018, 07:50:19 pm
content: A circuit breaker adds protection + manual switching. And it seems to me that you only need the latter. If this is the case I'd use a good relay. Also you could add a current detection circuitry to put a max on the current that opens the relay.That said, AC circuit breakers have response curves which means that they don't trip instantly when their nominal current is exceeded. So they don't behave like the current limit you have on your lab power supply. You could use a DC breaker (they look the same but rated for DC) but look and understand what the rating and curves (B,C,D..) mean and look like before ordering one.

author: Twoflower
author_rank: Frequent Contributor
timestamp: March 06, 2018, 08:06:07 pm
content: The problem with DC operation might be a standing arc in case a very hight current appears and the distance between the connectors is to small. The 48V are on the lower end to provide a standing arc. On AC the arc shuts down during the null-crossing (unless you feed much higher energies).So in worst case the CB will trigger but the current might still flow through the plasma of the arc (probably not because the low voltage). The smallest problem is contact burning and early fail after a few breaking events. Which again under worst case could fuse the contacts and renders the breaker unusable.Check the datasheet of the CB if they have any rating for DC. If not the breaker is probably not suitable for DC operation.

author: mtdoc
author_rank: Super Contributor
timestamp: March 06, 2018, 08:23:07 pm
content: No. AC breakers are not designed to handle the sustained arc created by DC.Use a properly rated DC breaker.For DIN mount, I recommendMidnite Solar breakers.They also makepanel Mount breakerswhich I can also recommend.For low voltage - such as 48V or below - there are other good options - breakers/switches designed for battery banks. For example seehese. (Note - these are rated for a maximum (not nominal) 48V).Midnite products are sold internationally. Check local solar PV suppliers. They may not carry MS products but will carry other brands of DC breakers.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: March 06, 2018, 10:35:58 pm
content: Quote from: mtdoc on March 06, 2018, 08:23:07 pmDoes it matter if it's rated for a higher voltage or the fact that it's a DC breaker is all that needs to be considered?

author: mtdoc
author_rank: Super Contributor
timestamp: March 06, 2018, 11:02:26 pm
content: Higher voltage rating is good. It can't be too high.You just want to be sure that the voltage in your circuit will not exceed the voltage rating - especially in a fault situation.BTW- I fixed the link to panel mount breaker in prior post.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: March 07, 2018, 09:45:25 pm
content: So I went and bought myself a Schneider Electric 25A DC circuit breaker and same thing happens.I was able to run 36A through it for an hour, it got very hot to the touch with some parts hot enough to burn my hands and the breaker didn't break!What is going on here? Is this not working like it's supposed to or am I missing something?Here's a link to the datasheet FYI :http://www.ekt2.com/pdf/852_BREAKER_DC_2POLE_25A_SCHNEIDER.pdf

author: Phoenix
author_rank: Frequent Contributor
timestamp: March 07, 2018, 10:37:44 pm
content: If you look at some circuit breaker curves an overload of 1.44pu is not much and may take a long time to triphttps://download.schneider-electric.com/files?p_enDocType=Catalog&p_File_Id=7825608832&p_File_Name=0860CT0201R1114+net.pdf&p_Reference=0860CT0201E.g. the tolerance for a 1 hour trip is shown as about 1.03pu to 1.3pu for a lot of them.Also do you have the contacts configured in series or parallel?