Leaf Precharge Circuit: Identifying parts

[Scrappyjoe]

Hello,

I have a leaf precharge circuit, and I'm trying to figure out how to wire it up, and how to control it. I have looked through the forum and through the wiki and can't find much, so I thought I'd ask here and make the answers into a wiki page. I don't have access to an actual Leaf to see how they are wired on an OEM vehicle. Apologies if this is documented somewhere - you can just send me to the right place!

I've attached a picture of my circuit, along with numbered annotations. Here are my questions.

1. What is the purpose of the brass rings next to each contactor? See (1) as an example.
2. Why are there 2 large contactors (annotation 2 and 3)? Are they supposed to be wired in parallel, with each contactor on the positive side of two battery packs, or are they supposed to be wired in series, with one on the positive end and one on the negative end of the battery?
3. Is (4) what forum discussions call the precharge contactor? Or is it something else? The precharge resistor perhaps?
4. How do I control these large contactors? Do I just supply 12v to (5,6,7) or do I have to control it via some protocol via the small pins at (8)?
5. How would I actually wire this guy up? I have a clue that the large wires are negative and positive HV, so I'd imagine that I simply connect those to the battery and the terminals (at (2) and in the fuse holder at (9)) to the other end of the HV circuit.
6. If these contractors are controlled independently, are they supposed to be controlled simultaneously, or separately, with some time lag?

[johu]

1. The brass rings are the mechanical bolting points for the contactors
2. One positive contactor (usually #3) and one negative (#2)
3. #4 is the precharge resistor. The precharge contactor is the part above it with the 4 wires
4. You just supply 12V. Economizing is optional, one pulls 500mA as far as I remember
5. Yes, fuse usually gets positive voltage from the battery and negative goes directly to #2 and it all comes out the other end
6. On ignition on you immediately close negative contactor #2 and precharge relay #4-ish. When voltage before and after the contactor block has like less than 20V delta you close #3 as well

The delta can be calculated by the BMS reported battery voltage and e.g. the voltage reported by the inverter, charger or DC-DC converter. Usually all these devices have CAN messages that contain this info.

[Scrappyjoe]

Thank you, johu. I'll put together a wiki page.

What is (8) for? Safe to ignore?

Edit: fixed johu's name, which had autocorrected to John!

[johu]

Oh those are the relay coils aka control signals!

5, 6 and 7 are for the PTC heater and battery heater. They are always on

[Scrappyjoe]

Thanks johu, this is very helpful. So if I have got this right, the means of controlling the contactors is via the plug labeled (8) above.

I have found a wiki page that relates to this contactor box here - https://openinverter.org/wiki/HV_Contactor_Box - but it's poorly named and could do with an update, so I'll transfer this info there.

A few more questions if I you have a little more patience - just so everything is totally explicit.

1. Looks like polarity of the precharge relay control wires matters so I will trace the pinouts, or, at least, the wire colours, and include in the wiki.
2. Does the polarity of the HV contactor coil wires matter?
3. So I see how we close a contactor or relay - by applying 12v.
4. But how do we keep it closed? Do we keep applying 12v?
5. When we are finished driving, how do we open the contactors? Just by cutting 12v?
6. If so, can we cut 12v simultaneously, or must it be phased in a similar manner to the starting procedure?
7. What happens if we lose 12v to these contactors while driving? Obviously our motor loses power, but does anything get dangerous or break?

[arber333]

7. What happens if we lose 12v to these contactors while driving? Obviously our motor loses power, but does anything get dangerous or break?

I can chime in here.
Up and around this forum i constantly warn on trusting the odd transistor with keeping your dc contactor latched.

Lets talk about consequences of dropping dc contactor first... when there is no battery load and motor is BLDC magnets keep generating voltage across dc capacitor inside inverter. When it reaches over 1200vdc IGBT will blow. This is not the same for ACIM motor which does not have active core.

So desired event would be to keep battery connected for as long as possible.
I promote the use of pair relays in latching circuit. One relay comes active when you provide start pulse and shows 12v to other relay coil. The second relay will be powered for as long as 12v is present. This will keep contactor closed even if your inverter brain goes off...

[jrbe]

... The second relay will be powered for as long as 12v is present. This will keep contactor closed even if your inverter brain goes off...

So ignition key off shuts them off?

[arber333]

Yes start key will turn the pair on and when you remove 12v they drop out. When i come home i will draw schematic for clarity.

[Scrappyjoe]

Ok, here is the outcome of this thread. Tomorrow I’ll add it to the wiki.

[Alibro]

7. What happens if we lose 12v to these contactors while driving? Obviously our motor loses power, but does anything get dangerous or break?

I've had this as a problem and in my case either it doesn't break stuff if the contactor loses power or I was lucky.
I followed Arber333's advice and connected a relay such that it latches on when it is powered by the VCU and will not unlatch until the ignition is turned off.
It is very simple to do, I used a double pole single throw (DPST) relay.
12V is delivered to the Pos side of the relay coil by the VCU when it sees the precharge has completed.
One side of the relay delivers 12V to the contactor and the other side delivers 12V to the positive side of the relay coil so once triggered it is latched on.

[Scrappyjoe]

Wiki page is here -


https://openinverter.org/wiki/Nissan_Le ... harge_Unit

[arber333]

I found one of my previous latching relay sketches..
viewtopic.php?p=41276#p41276

[Gregski]

this is great, exactly what I was looking for, thank you for the write up, I see there's a couple of them listed on eBay for under $150, I may get one for funsies

[Scrappyjoe]

Just double checking this, as nobody answered and google is not telling me.

Does the polarity of the coils or the contactor terminals matter? What I mean is, for the 12v connections, do we care what side is -ve and what is +ve? Similarly, for the HV terminals, do we care what is the battery side and what is the load side?

[uhi22]

If they have just coils the polarity does not matter. If they have internal electronics for economizing, the polarity may matter. Just connect a 12V supply, try both directions, measure the current and if you hear the same click and have the same current then you know each polarity is fine.
Also for the HV polarity, the contactor does not care.

[Scrappyjoe]

Brilliant, thanks uhi22!

[Scrappyjoe]

I'll just leave this here for anyone who is having trouble visualising a precharge circuit.