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Charging shutdown circuit question.

Fluffyboii

Member
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I am trying to recreate a part of that shutdown circuit in LTSpice but I am not getting the behaviour I expect from the optocoupler. First of all the original circuit uses the double pole relay to short the outputs of the optocoupler which is not something I understand the reason of. I think one of the contacts of relay used for latching but I am not sure how shorting the optocoupler outputs achieve that. I was also unable to find the exact optocoupler model for LTSpice in anywhere. It is a mosfet based opto instead of a BJT based one so its behavior is probably different.

The requirements of this circuit is that it consists of 3 stages and all of the stages must be clear for battery to recharge. If one of them gives error signal the progress halts until manual reset signal is applied to the optocoupler. The reason they use it is for galvanic insulation. Honestly I can build something similar with logic gates but I want to understand how this thing really works.
Can someone help me out, I am kinda lost and don't know where to start with this.
 

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crutschow

Well-Known Member
Most Helpful Member
I agree that the second circuit from the left does not make sense.
I can see how the ones with 12V to the relay work, but not the second.

Exactly what is the sequence of signals to that second circuit, and what are the expected actions?

(Noticed that the schematic is from the U of W-Madison.
I graduated there with a BSEE, summa cum (not even close) way, way back in 1963.)
 

rjenkinsgb

Well-Known Member
Most Helpful Member
The relay circuit looks fine. The red tags are presumably external "OK" or "permit" type signals, the first being at 12V to enable and the second grounded to enable.

They are latching relay circuits, "set" or latched on by the optocouplers if all the feeds are in the correct state; the opto completes the circuit through the relay coil between power & ground, then as the relay pulls in, one of its contacts maintains that path.

If eg. one of the red tag inputs changes state the appropriate relay no longer has power, switches off an breaks the overall Charge enable chain.

(I can't help with the sim side, sorry).
 

Fluffyboii

Member
The relay circuit looks fine. The red tags are presumably external "OK" or "permit" type signals, the first being at 12V to enable and the second grounded to enable.

They are latching relay circuits, "set" or latched on by the optocouplers if all the feeds are in the correct state; the opto completes the circuit through the relay coil between power & ground, then as the relay pulls in, one of its contacts maintains that path.

If eg. one of the red tag inputs changes state the appropriate relay no longer has power, switches off an breaks the overall Charge enable chain.

(I can't help with the sim side, sorry).
That is pretty much spot on.
from what I understand from here IMD_Fault is high when there is no IMD default state for some reason but the opto is normally closed so when the "set" is high it lets current to pass and relay closes and completes the circuit, thus latching and also closes the other terminal.

Reading the SAE rules it states that this circuit must be consisted with 3 parts for shut down button, Accumulator Management System (AMS) and Insulation Monitoring device (IMD). They all should be independent and have open contacts by default. I still don't understand how the opto works with the relay exactly and I can not recreate it so idk.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
the opto is normally closed
The optos are normally open. so when the Reset input is powered, it pulls the relays in, as long as the power feeds from whatever they monitor are in the correct states.

Each powered relay then latches itself, as long as its safety input stays at the correct voltage.

Think of the opto as the "on" button in a simple latching relay circuit, with whatever safety device controlling power as the "off" button; almost like this, except no B2 and "off" is by removing power to the whole circuit.

images
 

Fluffyboii

Member
The optos are normally open. so when the Reset input is powered, it pulls the relays in, as long as the power feeds from whatever they monitor are in the correct states.

Each powered relay then latches itself, as long as its safety input stays at the correct voltage.

Think of the opto as the "on" button in a simple latching relay circuit, with whatever safety device controlling power as the "off" button; almost like this, except no B2 and "off" is by removing power to the whole circuit.

images
Yes I am aware that optocouplers are essentially solid state relays. When I said closed I meant it was actually open at the outputs since there is no current present at its inputs, sorry for wrong wording. What I do not understand is when the lower terminal of the relay closes it shorts 3 and 4th pins of the opto in the sample circuit.
 
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rjenkinsgb

Well-Known Member
Most Helpful Member
What I do not understand is when the lower terminal of the relay closes it shorts 3 and 4th pins of the opto in the sample circuit.
It does exactly the same as the "B1" button in the relay diagram I posted - it bypasses the open relay contact so the relay pulls in, if the power to that part is on.

Once the relay is in the ON state, the "on" button or opto are irrelevant - they are just to activate things & the relay stays on until its power is lost.

(Ignore B2 in that circuit).
 

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