DIY Economiser for OEM Contactors

[jrbe]

I've been slowly working on this between other things. This s what I have currently.

The duty cycle is selectable with solder jumpers.
0 = 14.3%
1 = 17%
2 = 19.75%
3 = 21.8%
4 = 23.9%
5 = 26%
6 = 28%

My thought is to set this up with 3 solder jumpers shorted (that can be cut to open) to default to 21.8% duty cycle.

https://everycircuit.com/circuit/4973018295828480 is a simulation of the resistor stack with switches as solder jumpers.

- Anyone need more than 28% duty cycle for their contactor or any that they have seen needing more?

I'm planning to have a solder jumper for 20kHZ / 25kHz with 25kHz as default. Might be a solder jumper to cut for 20kHz as I'd prefer 25kHz as default so us sensitive people don't have to hear it.

I also have a solder jumper to short when using 20kHZ frequency that adds in a resistor across the voltage divider stack. This keep the load the same as 25kHz so the voltage and duty cycle are consistent between frequencies - according to Ti's specs in the DRV103 pdf. The switch on the bottom right switches between 20kHz and 25Khz load in the everycircuit link above.

Full on time I planned for 110ms, up to 550ms with 4 solder jumpers. Thinking to do all 4 solder jumpers as shorted by default. I cant imagine a 550ms on time will heat up / damage a contactor coil. Doing this for low voltage 12v batteries that might end up lower than 12 or 14v as most specs are written to. A car that wont engage contactors because the battery voltage is a bit low isn't ideal.

JP1 is a solder jumper to switch between + and - triggered for contactor #1. #2 will have a jumper as well.

Hole size is 60mm x 40mm currently, board size is 68mmx49.

The slots will work with soldering in wires directly. They are also sized for faston solder tabs like this,

image.png (8 KiB) Viewed 780 times

Also thinking of adding some slots below the wire area to use shrink wrap over the board and wires as a strain relief.

- Any input, requests, ideas, preferences, critiques, etc?

[jrbe]

V0.0 of this is done but not tested yet.
https://github.com/jrbe/2-Coil-Economizer-PCB

Allows different settings with solder jumpers. They are about $15USD each fully populated. You will have to pre order the drv103 chips from JLC though.

More info at github.

[Zieg]

WOW! That's absolutely amazing. When you say you have to pre order the DRV chip, do they still solder it or is it shipped loose? And is that included in the $15? Even if it isn't, $15 looks like a great price for all that.

[jrbe]

When you say you have to pre order the DRV chip, do they still solder it or is it shipped loose? And is that included in the $15?

They solder it if you pre order it. There's a minimum qty of 5 boards from JLC. It was a bit over $70 for 5 completely populated boards, then add shipping and tax.
You can have them only populate 2 of the 5 boards as an assembly option but the other 3 are component costs only, about $3 each, you don't save much.

Don't forget, not proven out yet, needs testing & maybe troubleshooting.

[jrbe]

I'm ordering a batch of 5 to test, I just pre-ordered the DRV103 chips.

I need to find a couple contactors without economizers to test with, even if their high voltage contacts are shot. Anyone know a part number / vehicle for 3 amp (coil) contactor and maybe where to find them cheap?

[jrbe]

I'm looking for feedback on contactor coil resistance. One of the contactors I see the most is the EV200AAANA. This has an economizer built in but has a coil resistance of 3.14 ohms for 4.6 amps at 14v. This is out of the range of the DRV103H,

Over Current Fault
An over-current fault occurs when the PWM peak output
current is greater than approximately 3.75A. The OK flag is
not latched.

I'm not sure if I'm just not finding contactors below 3A coil current or if its uncommon.

So, I'm thinking to up the current of this board. In the DRV103 datasheet it lists using it as a high side driver with a IRF4905 P channel mosfet. We don't need 70 amps but could look to use one for 10-15 amps or so per coil for about $3 more in components. That way it should be able to drive pretty much any EV contactor. This should also mean the pricey Tantalum capacitors would be no longer required. Will need to bump the Schottky diodes up too but the price of these is pennies.
The pc board might have to grow some to allow this. I might be able to fit them in by reducing the heatsink area of the DRV103h's. They wont be dissipating the power if the p - channels are driving the coils so the heatsinks can be reduced a lot.

Please let me know preferences / coil current rating / coil resistance.

[Zieg]

LEV200A4NAA is what I have in the car - 11 ohm coil.

Chrysler Pacifica battery has EVC500 contactors - 3.14 ohm coil. I have two on the shelf if that's any use.

Is it really a big problem to pull that much current just for the first 110ms though?

[jrbe]

This board is setup for the Powerpad SO-8 which has a thermal pad that gets soldered to the board. Its higher heat dissipation means it can carry more current. The normal SO-8 (non-powerpad version) is also drop in for this board but it doesn't have the heatsink, so only rated for 1.5A.

The DRV103H has the following info about current capacity:

HIGH OUTPUT DRIVE: 1.5A and 3A Versions

Current Limit(2), (10) 3 A min 3.5 A typ. 4.2 A max
(2) Output current resets to zero when current limit is reached.
(10) PowerPAD™ SO-8 (H) package has highest continuous current (2A) because the chip operates at a
lower junction temperature when underside metal tab is connected to a heat sink or heat spreader.

An over-current fault occurs when the PWM peak output current is greater than approximately 3.75A.

I've learned to not push Ti IC's near their ratings. I'm using one of their high side switches in another project and they keep failing with minimal load and well below their rated specs. They might be defective or counterfeit though too.

I do not see any info about the full on time current limit. Went digging at Ti's site,
https://e2e.ti.com/support/power-manage ... nt#3830294
They say to not use it for a 4A max coil.

The board design is set to default to 550ms currently.

Did any of the previous DRV103 boards get made & tested? I hesitate to overload the DRV103, it will likely drop out while driving along with pricy damage. I think its likely worth just adding the p-channel mosfets.

[Zieg]

Yeah, I have a copy of the previous design in my car and it's working. I don't have a lot of testing hours on it yet, but so far so good with the 11ohm contactors.

(This was taken when I removed it from the car to replace the screw terminal with a spring terminal)

[jrbe]

...I don't have a lot of testing hours on it yet, but so far so good with the 11ohm contactors.

That contactor is 1.27A with 11 ohms @ 14v.

Is that the heatsink version of the DRV103 on the board?

Do you have a spare board you could test with your Pacifica contactors?

[Zieg]

The DRV103s I have are all non-heatsink version (all that was available at the time I ordered them).

I do have two more unpopulated PCBs and a handful of components sitting around, will see if I can cobble something together. I'd also be happy to mail you one of the contactors if you'd like to try it with your new boards when they come in?

[jrbe]

Im going to do the P Mosfet route. Only downside i see is a bit of cost and board space.

Yeah, I'll take you up on that. I'll pm you my contact info soon. Might be a few days before I get back to working on this.

Edit, I don't think it's worth going through all that if it's the non heatsink version.

Edit 2, another downside of the p Mosfet route is limiting the voltage to the Mosfet vgs, so in this case 20v. There are some 30v vgs p Mosfets available but they're not as common. If anyone tries to use this with 24v they will need to hunt down 30v vgs p Mosfets. There are ways to work around this but to drive the PWM speed it gets tricky. None of this vgs stuff will be an issue for 12 / 14vdc.

[jrbe]

JLC just sent me an updated invoice for the DRV103H ICs I pre-ordered. They are about 3x the cost from what they were supposed to be.

I requested a quote for the 4 variants of this IC to be able to make a better informed decision on which to use in this design. It's not a show stopper but changes things some.

[jrbe]

I'm not sure why they assigned 4 part numbers, it's 2 variants with different assembly feed packaging...and screwed up pricing.

$2.47 for the 1.5 amp version without a heatsink.
$4.64 for the 3 amp heatsink version.

The heatsink on the DRV103 is required to be separate from the ground plane. It looks like the heatsink version could let out a bunch of emi.

I did the design with P mosfets. I didn't fully work through the gate capacitance / resistor simulation but got it close. I'm planning on adding through hole solder resistor footprints if the resistors need to be adjusted.

I'm planning on using the non heatsink DRV103 as it's only turning on the p mosfet. I think there will be less emi as well going this direction.

[jrbe]

This is the simulation I was doing to find reasonable resistors for the gate as well as for testing the zener to protect the p mosfet.
https://everycircuit.com/circuit/4697508156276736
The green trace there is watching VGS.
There's a switch to swap between 12v & 24v.
This runs at 25kHz. Its looking like a 100ohm resistor to the DRV103 output and a 3k pull up to +VDC, along with the zener to keep VGS in check. Everycircuit has some uncommon settings for mosfets that I'm not familiar with so Its hard to know what specs they are accounting for.
I added a switch with a capacitor to add gate capacitance in to the simulation, but not sure if there is any in the p mosfet already..

I was thinking to leave the zeners out for 12v usage but its cheap protection using this in a noisy / spikey automotive use. It should also allow it to be used in 24v systems without other changes.

The board grew a bit adding the p mosfets. I also need to get rid of the heatsinks and make those back to ground planes. While I do that I'm going to try to shorten up the traces to the jumpers for the different settings.

Its still pretty small and should be able to drive 10a coils for pull in.

The p mosfet I'm planning is a Vishay SUD50P10-43L-E3 / C913430 / https://jlcpcb.com/partdetail/VishayInt ... E3/C913430
Its a 100v, 20v VGS, .043 ohm RDS on, rated for over 30 amps, & $1.57 ea. They are common and fairly cost effective. So swapping to the p mosfets and the 1.5a DRV103's it should be cheaper and 3x more powerful than the 3a version DRV103's.

Input, feedback, schematic review, etc. are all appreciated.

PWM Economizer V1.0 prelim.pdf

(541.42 KiB) Not downloaded yet

[jrbe]

I was going to only spend 30 min on it but got stuck in it.

Getting rid of the heatsink planes made a big difference. I was able to shift things around and tighten up the traces for frequency and pwm delay a lot. The ground plane is almost completely solid except for 1 duty cycle reference voltage trace that had to hop over another.

Board is back down to 55mm tall x 68mm wide.

I have a bit more time to do the gerbers & fabrication files still.