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Discussion Starter · #1 ·
Hi,

my name is Alex and I'm currently building an Essex 1928 EV Conversion.
Everthing is set up and the system is running so far exept for the DCDC converter.
The manual isn't very clear about the pin definition, colors of wires change and connectors look different than in reality.
So I connected it to the system but it doesn't output voltage (should be around 14V) - therefore it doesn't charge the 12V battery.
I found a post on the internet with someone facing exact the same issue, so I'm trying it here.
Also it should be the CAN Version, so I also tried to connect it to the CAN network - didn't work either.
Regarding my ev part distributer the brown wire (Pin 4) of the connector is the Enable Pin, which should be connected to 12V.
I attached the photos for reference.

Microphone Line Camera accessory Audio equipment Gas


The manual is also attached.

So I hope for any useful answers and thoughts.
 

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That picture is pretty self-explanatory. There is enable signal for which you need to apply another source of +12v. I assume it references the chassis for the negative, but it would be good to see the pinout for that entire connector to confirm.

It is kind weird to design a DC-DC that will require the same votlage to operate as the one it outputs! But that's the Chinese engineering for you.
 

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Same nominal-voltage inputs and outputs are pretty common in the DCDC converter world generally.

Sometimes the input range is pretty darn wide, maybe 10V-18V

but you want a specific precise output, say 13.8V.

Also when current limiting is required, rather than just latch/hiccup style OCP
 

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Discussion Starter · #4 ·
That picture is pretty self-explanatory. There is enable signal for which you need to apply another source of +12v. I assume it references the chassis for the negative, but it would be good to see the pinout for that entire connector to confirm.

It is kind weird to design a DC-DC that will require the same votlage to operate as the one it outputs! But that's the Chinese engineering for you.
The picture is actually a photo from my own converter - I named the connections as I connected them.
In the manual I attached is the original schematic, where the pin connector looks different and the description is not really clear.

Due to it is used in a car I only have one 12V source. Would be akward if I had to use another 12V source to enable the converter.

Also the input voltage is 96-140V and the output voltage is 12V (in fact it has to be 14V to charge the battery like an alternator)
So it takes the High Voltage from the traction pack to charge the 12V system.

My only question is, how to activate the converter and what the exact pin definition is because I really tried many different ways and pins to enable this thing
 

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Discussion Starter · #6 ·
But logically it must be unimportant for the dc converter where the 12V comes from. It doesn't know if it's provided by the bms or the battery itself.
Except I use the CAN interface (which I'm not) so the BMS can tell the converter to start.
But it has to work without CAN I guess.

Also this connector is 4x1 but mine is 2x2.
This is what really freaks me out because I can't find any plan where there is the connector which is on my converter...
These chinese manuals really tick me off
 

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But logically it must be unimportant for the dc converter where the 12V comes from. It doesn't know if it's provided by the bms or the battery itself.
Except I use the CAN interface (which I'm not) so the BMS can tell the converter to start.
But it has to work without CAN I guess.

Also this connector is 4x1 but mine is 2x2.
This is what really freaks me out because I can't find any plan where there is the connector which is on my converter...
These chinese manuals really tick me off
Yes, it can be a 12v battery, as long as the negative is tied to the chassis of the converter itself. The only reason I specifically talked about it is the fact it's rather silly for EVs to carry 12v batteries. The whole point of DC-DC converters with 12v output is to power the 12v equipment from the main battery.
 

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It is standard in many if not most production EVs, but what is the point of it ? There is no standard equipment that would produce significant peak loads that the DC-DC wouldn't be able to handle directly. Not having to run main power contactor(s) just to power DC-DC when vehicle isn't running ?
 

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When the Hv contactors are open, they are open. That means no HV anywhere on the car. Anywhere.

No HV, no power anywhere...on a rainy night, you just rear ended someone, airbag went off, contactors opened, a dumptruck is barrelling in on the crash scene.

Flick your Bic?
 

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That's the common design pattern, but it doesn't need to be that way. So like you suggested there is a legitimate interest to interrupt HV in case of a crash, fine... but if the DC-DC is buried into the pack, along with BMS, then there is no HV coming out of the pack.
 

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You need to remember why disconnecting the HV is important, and legitimate. Idea is that on production EVs battery pack is enclosed into a self-contained, somewhat armored shell and is installed in a predictable location, such as vehicle's underbody. So if the rescue team needs to chew through the vehicle to get to the occupants, as long as they stay outside of the battery box, there is a reasonable expectation that no HV will be supplied to any other part of the vehicle. It's not 100% either, but it's a lower risk. Inside the battery box you can do whatever you want though, since no matter how you look at it, battery box remains under HV even when contactors are open.
 

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Discussion Starter · #18 ·
So technically it isn't necessary to have a 12V battery but I also think it's important for safety reasons (although the car I have converted doesn't have any safety features due it's an 1928 oldtimer :p)
I wonder if anyone has the same issues because this is one of the most common DC converters for EV conversions I guess.
 

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Tell me what it is after a 60g crash....
In engineering we talk about these things in terms of "failure modes." Please articulate which failure modes you anticipate that are either absent altogether or significantly altered by addition of DC-DC the way I described. There are already lines in the system, both High and Low voltage that can be impacted by a crash. There are already additional devices that can be impacted. There are batteries themselves that can be impacted. You're not worried for example that BMS would get confused and close the contactors when they should be open ? Or how about BMS getting electrically and/or mechanically damaged and applying HV say to CAN lines ?
 
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