# About Contactor Placement and Pre-Charge Circuits



## iruraz (Sep 4, 2012)

Dear All,

There are 2 figures in attachment file. green numbers 1 and 2 indicates contactors. And E is for emergency connection. I am not sure about placement of contactor 1. I intend to use 2.2kW delphi dc-dc convertor. Our ignition switch works with 2 levels. At 1st level, contactor 1 is on and dc-dc converter starts to supply aux. battery. When ignition switch is at 2nd level battery pack starts to supply power train (controller+inverter+motor). Which placement for 1st contactor is better than other? 

And other question is about precharge circuit. I need to use pre-charge circuit with 2nd contactor for controller which in power train. I know controller capacitance value. But I don't know whether I should use pre-charge circuit or not before dc-dc converter. I know that I should consider all capacitive load for pre-charge circuit. And is there any effect of hvac for calculation pre-charge circuit?

Thanks in advance.

Regards.


----------



## Ziggythewiz (May 16, 2010)

The DC-DC doesn't really need a big contactor. You probably want it always on or turned on with the controller so the DC-DC doesn't rob the pre-charge current.


----------



## major (Apr 4, 2008)

iruraz said:


> Dear All,
> 
> There are 2 figures in attachment file. green numbers 1 and 2 indicates contactors. And E is for emergency connection. I am not sure about placement of contactor 1. I intend to use 2.2kW delphi dc-dc convertor. Our ignition switch works with 2 levels. At 1st level, contactor 1 is on and dc-dc converter starts to supply aux. battery. When ignition switch is at 2nd level battery pack starts to supply power train (controller+inverter+motor). Which placement for 1st contactor is better than other?
> 
> ...




http://liionbms.com/php/wp_ignition_conundrum.php 

http://liionbms.com/php/precharge.php 

Here are a couple of resources on the subject.

Personally I like to use two contactors, one in the negative battery feed and one on the positive battery line. The negative contactor comes on first and the DC/DC will connect. Then the positive contactor with a precharge for the main controller. This provides a redundancy and complete isolation (of both + & -).

A 2.2 kW converter is pretty big and may have internal caps which will draw an arc upon connection. The same with an HVAC system. So you may need to precharge these accessories.

Of course the battery needs to be fused. And all the branch circuits going to the accessories need to be appropriately fused. You can also have interaction between the motor controller and accessories like DC/DC which require filters. The controller manual should warn of this and there have been a few threads on that subject.

Here is a sticky thread on the subject as well: http://www.diyelectriccar.com/forums/showthread.php/ev-high-voltage-turning-and-off-25318.html


----------



## iruraz (Sep 4, 2012)

@Ziggythewiz,



> The DC-DC doesn't really need a big contactor. You probably want it always on or turned on with the controller so the DC-DC doesn't rob the pre-charge current.


Actually, I don't intend to use contactor for DC-DC converter. DC-DC converter alway connects to battery pack. Is there any fault or hazard for this option?

@major,



> http://liionbms.com/php/wp_ignition_conundrum.php
> 
> http://liionbms.com/php/precharge.php
> 
> ...


Thanks for links. I read them before. As you mentioned above I will use 2 contactors for traction pack, hvac compressor and heater. I will isolate them from battery pack when ignition is off. 



> Of course the battery needs to be fused. And all the branch circuits going to the accessories need to be appropriately fused. You can also have interaction between the motor controller and accessories like DC/DC which require filters. The controller manual should warn of this and there have been a few threads on that subject.


Here is my updated schematic. There is no value for fuses and pre-charge resistor. For pre-charge resistor value I need to specify capacitance value for hvac compressor and heater. I would like to know your comments about last schematic.

FU indicates "fuse" in the schematic.
LOAD1 indicates loads which are always on (for instance: vehicle management unit, instrument cluster etc.)
LOAD2 indicates loads which are on when ignition on (level2) (for example: wipers, windows lifter, high-low beams etc.)

Regards.


----------



## major (Apr 4, 2008)

iruraz said:


> I would like to know your comments about last schematic.


Fuses need to be at the source. Besides that; looking better


----------



## iruraz (Sep 4, 2012)

@major,



> Fuses need to be at the source.


Sorry but I don't understand what you mean..

Regards.


----------



## major (Apr 4, 2008)

FU1 needs to be adjacent to the battery not the controller. The fuse for the 12V needs to be adjacent to the 12V battery before the node. Branch fuses need to be at the node with the main.


----------



## iruraz (Sep 4, 2012)

@major,



> FU1 needs to be adjacent to the battery not the controller. The fuse for the 12V needs to be adjacent to the 12V battery before the node. Branch fuses need to be at the node with the main.


Thanks for your advice. Should I use common fuse for controller+hvac compressor+heater before power line(+) branch off? (I mean that after contactors and before branch)

Regards.


----------



## major (Apr 4, 2008)

iruraz said:


> @major,
> 
> 
> 
> ...


The fuse is to protect the circuit. Putting two power components on a common branch causes you to size the fuse for the sum of the current for two loads and use larger wire to each load. It is best to have power loads like that on separate branches each with appropriate fuse. For non-power loads like instruments and lights and such, it makes sense to have multiple devices on a single branch fused for the sum. Think of it as the fuse protecting the wire running from the source to load. If the load shorts out or if the wires short together at any point, the fuse needs to blow before any section of that wiring overheats and starts a fire.

edit: You need a fuse at the main HV battery. You don't need another fuse for the controller. But you do need another smaller fuse for each branch coming off the HV main line.


----------



## Ziggythewiz (May 16, 2010)

iruraz said:


> @Ziggythewiz,
> Actually, I don't intend to use contactor for DC-DC converter. DC-DC converter alway connects to battery pack. Is there any fault or hazard for this option?


Just be aware of any parasitic loads and use a maintenance disconnect if the car will be uncharged long enough for those loads to be a problem.


----------



## iruraz (Sep 4, 2012)

@major,



> It is best to have power loads like that on separate branches each with appropriate fuse.





> You need a fuse at the main HV battery. You don't need another fuse for the controller. But you do need another smaller fuse for each branch coming off the HV main line.


I redrew schematic according to your advice. I added a main fuse after battery pack. But I am confused about its place. Is it better after "hvac compressor" and "heater" branch? If I replace it after "compressor" and "heater" branch, I think I don't need FU1. If I am wrong correct me please.

@Ziggythewiz,



> Just be aware of any parasitic loads and use a maintenance disconnect if the car will be uncharged long enough for those loads to be a problem.


Could you give me details about parasitic loads? 

And other question about "compressor" and "heater" contactors. Do I need to isolate them from battery pack with two contactors? Or is one connector enough like in the schematic? Do I need pre-charge circuit for compressor and heater? 

As I mentioned before heater and compressor are ready to work when ignition level-2 with traction pack (controller+inverter) according to my plan. I am not sure about controlling inrush current. Should I activate heater and compressor after traction pack?

Thanks in advance.

Regards.


----------



## Siwastaja (Aug 1, 2012)

Move the fuse even further, INTO the battery pack, or as close as possible. Emergency disconnect comes after the fuse. Yes, you can then remove FU1, it's redundant.


----------



## major (Apr 4, 2008)

iruraz said:


> @major,
> I redrew schematic according to your advice. I added a main fuse after battery pack. But I am confused about its place. Is it better after "hvac compressor" and "heater" branch? If I replace it after "compressor" and "heater" branch, I think I don't need FU1. If I am wrong correct me please.


Hi iru,

I said it before and say it again. Put a fuse at each source and at each branch. So, like Siw says, put the main fuse in the battery or adjacent to it. Then you do no need another fuse to the controller; it is redundant.

You need a fuse in the branch supplying the DC/DC.

Move FU3 to be adjacent to the 12V battery.

A fuse on the output of the DC/DC is not needed.

Fuses on the 12V branches are up to you (typically the existing automotive fuse block is used).

HVAC branch has an error.

I typically locate the main negative contactor just after the E disconnect so that it powers down everything including the DC/DC (eliminates the parasitic draw).

WRT the HAVC and heater needing inrush or precharge; it depends on the particular equipment you have. Check the manuals or with the supplier or run a test and see.

major


----------



## PTCruisin (Nov 19, 2009)

If it is possible, I would suggest that you place the fuse mid-pack such that in the event of a failure the pack is split.


----------



## iruraz (Sep 4, 2012)

@Siwastaja, @major, @PTCruisin thanks for your recommendations.

I redrew it.

@Siwastaja,



> Yes, you can then remove FU1, it's redundant.


I removed FU1, but now there is not fuse protection for controller. Becaue FU-MAIN= FU2 + FU4 . There is current which is bigger than controller capacity. How is controller protected against to big current? 

Regards.


----------



## major (Apr 4, 2008)

iruraz said:


> I removed FU1, but now there is not fuse protection for controller. Becaue FU-MAIN= FU2 + FU4 . There is current which is bigger than controller capacity. How is controller protected against to big current?


You still do not have a fuse on the DC/DC converter input branch.

And the fuse will not protect the controller; it protects the circuit. Your controller must be capable of limiting the current. Once it fails to do that, it is toast anyway and then the fuse blows and keeps the circuit from burning down the system.

The reason most applications use only a main battery fuse and no secondary fuse in the controller branch is because the magnitude of current is so close. For instance, a 400A main fuse is used in the battery and sized for all loads. The auxiliary loads might be on the order of 30 Amps. It is impractical to try to further fuse the controller at 370A. It would be required if the controller branch dropped in wire gauge or if for some reason you required auxiliary equipment operation in the event of a controller failure.


----------



## iruraz (Sep 4, 2012)

@major,



> You still do not have a fuse on the DC/DC converter input branch.
> 
> And the fuse will not protect the controller; it protects the circuit. Your controller must be capable of limiting the current. Once it fails to do that, it is toast anyway and then the fuse blows and keeps the circuit from burning down the system.
> 
> The reason most applications use only a main battery fuse and no secondary fuse in the controller branch is because the magnitude of current is so close. For instance, a 400A main fuse is used in the battery and sized for all loads. The auxiliary loads might be on the order of 30 Amps. It is impractical to try to further fuse the controller at 370A. It would be required if the controller branch dropped in wire gauge or if for some reason you required auxiliary equipment operation in the event of a controller failure.


I redrew it according to your warnings. Thanks for your helps and patience.

Regards.


----------

