Newb Asks: How do we connect the HV of the DC-DC Converter

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Gregski
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Newb Asks: How do we connect the HV of the DC-DC Converter

Post by Gregski »

looking for advice on how to wire the DC-DC converter, I plan on using the Chevy Volt first gen one (to start anyway) just looking for a basic simple solution nothing fancy

is it ok to have it on the battery pack side of the contactors or do we have to connect it on the switched side of the contactors, I am essentially just looking to use the contactor studs as a junction block for this (I do plan on having a 20 am fuse to protect the converter as well)

please and thank you, a Gregio v1.0 diagram is provided to illustrate what i am trying to ask

HV Wiring Diagram Converter.jpg
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Re: Newb Asks: How do we connect the HV of the DC-DC Converter

Post by mjc506 »

Swings and roundabouts.

Most OEMs seem to have the inverter, dcdc and charger on separate sets of contactors. (or variations of that) This allows each system to be powered up or made safe separately, for example, during charging the charger needs to be powered, having dc-dc powered is useful :-) and it's nice to have the inverter powered off (no chance of a driveaway with the cable plugged!). Then you add another set of contactors for DC charging... This does all require more complex control, and more complexity can mean higher costs and higher chance of problems.

My Ioniq PHEV has the battery in the rear of the vehicle, but all the HV stuff in the front (and no DC charging). So it has a single set of contactors at the battery, and powers everything on/off at once (so when you plug it in to charge, the contactors are closed, and the inverter is also powered). Much simpler, but relies on the inverter not deciding to take off on its own (although, if the inverter is controlled over CAN or similar, it won't move without receiving the right messages, so...). If the car is sat for a long time, the 12V battery can run a little low (so many computers powered up all the time), so it will occasionally close the contactors and run the dc-dc to top it up.

Your diagram would keep the DC-DC powered all the time, so you wouldn't need to worry about contactors to keep your 12v battery topped up, and don't have to worry about precharge (except maybe the first time :-) ) The downsides include having a section of HV wiring live all the time (so you'll therefore probably want to keep your dc-dc/charger as close to the battery as possible, and the potential for a rogue DC-DC to flatten your traction battery. The upside is that you can keep your inverter turned off with the ignition (more useful perhaps if you also have your AC charger connected before your contactors, but same downsides as above)

I would be tempted to avoid using the contactors as junction blocks. The more joints you have there, the greater the resistance, and the more potential for vibration to loosen things up. Yes, plenty of ways to mitigate that but... A better option (in my opinion) would be a couple strips of copper as bus bars - these can be solidly mounted and have plenty of things bolted to them. This does drop into 'junction box' territory though, so will take up more space.
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Re: Newb Asks: How do we connect the HV of the DC-DC Converter

Post by Gregski »

mjc506 wrote: Fri May 06, 2022 4:08 pm Swings and roundabouts.

Most OEMs seem to have the inverter, dcdc and charger on separate sets of contactors. (or variations of that) This allows each system to be powered up or made safe separately, for example, during charging the charger needs to be powered, having dc-dc powered is useful :-) and it's nice to have the inverter powered off (no chance of a driveaway with the cable plugged!). Then you add another set of contactors for DC charging... This does all require more complex control, and more complexity can mean higher costs and higher chance of problems.

My Ioniq PHEV has the battery in the rear of the vehicle, but all the HV stuff in the front (and no DC charging). So it has a single set of contactors at the battery, and powers everything on/off at once (so when you plug it in to charge, the contactors are closed, and the inverter is also powered). Much simpler, but relies on the inverter not deciding to take off on its own (although, if the inverter is controlled over CAN or similar, it won't move without receiving the right messages, so...). If the car is sat for a long time, the 12V battery can run a little low (so many computers powered up all the time), so it will occasionally close the contactors and run the dc-dc to top it up.

Your diagram would keep the DC-DC powered all the time, so you wouldn't need to worry about contactors to keep your 12v battery topped up, and don't have to worry about precharge (except maybe the first time :-) ) The downsides include having a section of HV wiring live all the time (so you'll therefore probably want to keep your dc-dc/charger as close to the battery as possible, and the potential for a rogue DC-DC to flatten your traction battery. The upside is that you can keep your inverter turned off with the ignition (more useful perhaps if you also have your AC charger connected before your contactors, but same downsides as above)

I would be tempted to avoid using the contactors as junction blocks. The more joints you have there, the greater the resistance, and the more potential for vibration to loosen things up. Yes, plenty of ways to mitigate that but... A better option (in my opinion) would be a couple strips of copper as bus bars - these can be solidly mounted and have plenty of things bolted to them. This does drop into 'junction box' territory though, so will take up more space.
oh wow what a fantastic answer, "Swings and roundabouts." ha ha I am so stealing that

I think I should have shared that I also plan on using the Chevy Volt first gen charger which is unique in the sense that it is two chargers in one, one charges the big high voltage traction battery and the other the small low voltage regular car battery, so that takes care of the car battery running low from sitting issue, I think

the part about the DC-DC converter high voltage cables always being live is enough to convince me to move it to the other side of the contactors

however that just kicks the can down the road, as now I have a charger with live leads on it (oh well safer than having the car take off whilst charging, is it not?)

so here is the revised v2.0 wiring diagram (for dummies)
HV Wiring Diagram.jpg
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Re: Newb Asks: How do we connect the HV of the DC-DC Converter

Post by mjc506 »

So if your Volt charger also charges the 12V system, what are you using the DC-DC for? :-)

Are you using the Lexus inverter over CAN? Even with 12V and HV applied, it won't move if you don't send torque commands (and I think there's also an 'enable' or 'inhibit' 12V connection too? The Prius inverters do). I can understand not wanting the inverter powered while charging though.
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Re: Newb Asks: How do we connect the HV of the DC-DC Converter

Post by Gregski »

mjc506 wrote: Fri May 06, 2022 4:33 pmSo if your Volt charger also charges the 12V system, what are you using the DC-DC for? :-)
essentially as an alternator whilst driving, since I am not plugged into the wall whilst on the freeway
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Re: Newb Asks: How do we connect the HV of the DC-DC Converter

Post by mjc506 »

Ah, ignore me, I'd assumed that the charger would also do the DC-DC while driving too!
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Re: Newb Asks: How do we connect the HV of the DC-DC Converter

Post by arber333 »

Gregski wrote: Fri May 06, 2022 4:38 pm
essentially as an alternator whilst driving, since I am not plugged into the wall whilst on the freeway
I would advise you to connect DCDC directly to HV across 30A fuse.
If you connect it behind DC contactor you must wait after precharge is done otherwise strange things may happen.

Maybe you can use those HV solar fuses on the cable for both Charger and DCDC.
https://www.aliexpress.com/item/4000402 ... 1354%7Csea
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Re: Newb Asks: How do we connect the HV of the DC-DC Converter

Post by mjc506 »

Yes, good point - having a running dc-dc (or anything) drawing current through the precharge resistor will either prevent precharge from completing, cook the precharge resistor, or both!
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Re: Newb Asks: How do we connect the HV of the DC-DC Converter

Post by Gregski »

arber333 wrote: Fri May 06, 2022 5:24 pm
Gregski wrote: Fri May 06, 2022 4:38 pm
essentially as an alternator whilst driving, since I am not plugged into the wall whilst on the freeway
I would advise you to connect DCDC directly to HV across 30A fuse.
If you connect it behind DC contactor you must wait after precharge is done otherwise strange things may happen.

Maybe you can use those HV solar fuses on the cable for both Charger and DCDC.
https://www.aliexpress.com/item/4000402 ... 1354%7Csea
wouldn't a simple 10 second delay before sending an enable to the converter circumvent that from happening? I honestly don't know I'm asking
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Re: Newb Asks: How do we connect the HV of the DC-DC Converter

Post by arber333 »

Gregski wrote: Fri May 06, 2022 7:04 pm wouldn't a simple 10 second delay before sending an enable to the converter circumvent that from happening? I honestly don't know I'm asking
Hm.. You could just send CAN telegram with a delay (well not a delay function but millis...) 3000ms later from when you apply enable.
But why not keep the connection allways since DCDC does not run if there is no CAN msg. I kept it running for like 1/2 of year then i changed to outlander DCDC which i kept connected as well.

Currently i have Volt Gen2 DCDC which keeps on running at 13.6V even without PWM signal which is annoying. But it keeps aux battery happy.
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Re: Newb Asks: How do we connect the HV of the DC-DC Converter

Post by Gregski »

arber333 wrote: Fri May 06, 2022 7:41 pm
Gregski wrote: Fri May 06, 2022 7:04 pm wouldn't a simple 10 second delay before sending an enable to the converter circumvent that from happening? I honestly don't know I'm asking
Hm.. You could just send CAN telegram with a delay (well not a delay function but millis...) 3000ms later from when you apply enable.
But why not keep the connection allways since DCDC does not run if there is no CAN msg. I kept it running for like 1/2 of year then i changed to outlander DCDC which i kept connected as well.

Currently i have Volt Gen2 DCDC which keeps on running at 13.6V even without PWM signal which is annoying. But it keeps aux battery happy.
thank you for that additional feedback really appreciate it, and now you know why I posted this I was going back and forth 73 times so I figure this may be the EV equivalent of "hey which spark plugs are best" question, ha ha

so now that we got that unsettled, which side does the charger go on?

DC-DC Converter.jpg
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Re: Newb Asks: How do we connect the HV of the DC-DC Converter

Post by SciroccoEV »

Gregski wrote: Fri May 06, 2022 7:04 pm wouldn't a simple 10 second delay before sending an enable to the converter circumvent that from happening? I honestly don't know I'm asking
An enable delay is a common OEM solution. If the DC/DC output isn't enabled, then it shouldn't to put enough load on the precharge circuit to prevent it doing its job.

You are now reliant on having charge in the 12v battery to turn the car on and a flat 12v battery is a common cause of EV breakdown.

There is a solution to that and it's one that EV conversions were using 30 years ago. You have a momentary switch that can supply HV power to the DC/DC Converter, so that you have power to close the main contactors, which now of course power the DC/DC. The only OEM EV that used that trick was the GM EV1, which had a boostrap button hidden under the dashboard. This does have a safety downside, as it needs a permanent live HV feed, so a seperate power supply located inside the battery casing with an external mechanical means of enabling it might be worth considering.

Another solution is to monitor the 12v battery and power up the DC/DC if it drops too low.
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Re: Newb Asks: How do we connect the HV of the DC-DC Converter

Post by arber333 »

SciroccoEV wrote: Fri May 06, 2022 8:23 pm Another solution is to monitor the 12v battery and power up the DC/DC if it drops too low.
I use that one with Outlander DCDC which was obliging enough to transmitt all kinds of data over its CAN bus. I simply made my DUE listen for 12V going too low and command a 3 minute DCDC session. That still works in my Mazda keeping its 30Ah battery topped off.

I would not go for the HV button because it adds complexity and risk. Are battery connected DCDC and charger risk as well? Might be, but they are behind the fuse and their logic prevents them from randomly turning on.
Which is why i am annoyed by Gen2 DCDC. I just might put it behind an HV relay.
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Re: Newb Asks: How do we connect the HV of the DC-DC Converter

Post by muehlpower »

I have all devices after the main switches. Inverter, DC-DC-converter, AC-compressor, battery heater, cabin heater and onbboard charger are precharged with the precharge circuit and activated if needed after the main contactor is closed. The 12V battery is not charged when parking like on any ICE car. The advantage is that I don't have any hot HV lines when the ignition is switched off. The contacts are in the battery box. No 12V in means no HV out.
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