How much 12v power can we pull continuously thru 12v connections from HV battery?

dtbaker61

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I'm doing a little research before embarking on my 'next' DIY project with the MME..... I'd like to confirm how much power the onboard dc-dc system can xfer from HV battery to LV connection points 'continuously' if needed. And, to verify what conditions or state of 'on' the MME has to be in to allow 12v power draw for hours.

I've seen somewhere that the dc-dc can support up to 160amps continuously, which is right around 2000watts at 12.5volts under load. But, I can't remember where I saw it documented. Anybody have a source or specs from the dc-dc unit itself?

I am assuming that I have to have the vehicle 'on', and leave it 'on', for the HV to watch the LV and keep it charged if it were under some continuous significant 12v load?

 

ChasingCoral

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I'm doing a little research before embarking on my 'next' DIY project with the MME..... I'd like to confirm how much power the onboard dc-dc system can xfer from HV battery to LV connection points 'continuously' if needed. And, to verify what conditions or state of 'on' the MME has to be in to allow 12v power draw for hours.

I've seen somewhere that the dc-dc can support up to 160amps continuously, which is right around 2000watts at 12.5volts under load. But, I can't remember where I saw it documented. Anybody have a source or specs from the dc-dc unit itself?

I am assuming that I have to have the vehicle 'on', and leave it 'on', for the HV to watch the LV and keep it charged if it were under some continuous significant 12v load?
I’ll have to find the source but I posted this. ~1.6 kW continuous draw.
 

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The available converter current for off-car use is the max rated converter output current, minus the current the MME itself is using and/or needs (which can be minimized somewhat by turning the headlights from auto to off if dark, climate off, etc.). Also, be sure the converter rating is continuous, and not some limited duty cycle rating for peak available current for some limited duration.

With various MME system cycling on and off, the MME portion could be as high as about 400 watts at times.

Also, check the wire gauge of any existing MME circuits that might be in series with your mod. If #2, they might be running at or above 90C (194F) by 135A. We ran into this temperature question often when adding inverters to the Chevy Volt. Many of us decided that we were not comfortable running some of the interconnects near the temperature of boiling water (even where the insulation was rated at 105C). If the converter can safely supply current at or above 100A, it may be possible to replace those wires/cables with larger ones (if they are #2).
 
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ChasingCoral

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I'm doing a little research before embarking on my 'next' DIY project with the MME..... I'd like to confirm how much power the onboard dc-dc system can xfer from HV battery to LV connection points 'continuously' if needed. And, to verify what conditions or state of 'on' the MME has to be in to allow 12v power draw for hours.

I've seen somewhere that the dc-dc can support up to 160amps continuously, which is right around 2000watts at 12.5volts under load. But, I can't remember where I saw it documented. Anybody have a source or specs from the dc-dc unit itself?

I am assuming that I have to have the vehicle 'on', and leave it 'on', for the HV to watch the LV and keep it charged if it were under some continuous significant 12v load?
Here's the source and reference to "up to" 160A. unfortunately, it doesn't speak to continuous load. Just as a guess, I'd keep continuous loads at no more than 75% of peak load, so about 1.4kW/120A. Maybe @SnBGC knows the continuous limit.

DC-DC operation.png
 
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dtbaker61

dtbaker61

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Here's the source and reference to "up to" 160A. unfortunately, it doesn't speak to continuous load. Just as a guess, I'd keep continuous loads at no more than 75% of peak load, so about 1.4kW/120A. Maybe @SnBGC knows the continuous limit.

DC-DC operation.png

perfect.... looks like 160amp 'max', so I'll check wire sizes as well to verify continuous use limits.

I am working on a little system to run critical loads from the MME in case of emergency, camping, or at job sites not having AC power.
 


louibluey

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The water cooling by the electric motor cooling system is a both a blessing (excellent, efficient cooling) and curse. (Volt's APM was air cooled by a relatively low power fan.). I suspect the fluid pump, valves, and power to operate the louvers combined at times, might be a substantial load on the 12V system (part of that persistent 400 Watts or so).
 

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perfect.... looks like 160amp 'max', so I'll check wire sizes as well to verify continuous use limits.

I am working on a little system to run critical loads from the MME in case of emergency, camping, or at job sites not having AC power.
Keep us informed. My current option for that involves removing the panels in the Frunk area to get at the 12v and hook up an inverter.
 
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dtbaker61

dtbaker61

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The water cooling by the electric motor cooling system is a both a blessing (excellent, efficient cooling) and curse. (Volt's APM was air cooled by a relatively low power fan.). I suspect the fluid pump, valves, and power to operate the louvers combined at times, might be a substantial load on the 12V system (part of that persistent 400 Watts or so).

yeah, I would guess that if and when there is heavy load on the dc-dc it wakes up the coolant system.... there could be some additional parasitic load there, but dc-dc are usually fairly efficient, and putting thru 1.5kw it would probably only be dumping 25-50watts of heat, so, probably not kick on the heat pumps.... but we'll see!
 

ChasingCoral

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yeah, I would guess that if and when there is heavy load on the dc-dc it wakes up the coolant system.... there could be some additional parasitic load there, but dc-dc are usually fairly efficient, and putting thru 1.5kw it would probably only be dumping 25-50watts of heat, so, probably not kick on the heat pumps.... but we'll see!
Definitely don't expect dc-dc to generate as much heat as charging.
 

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Can you make the two 12 volt ports hot all the time ?
Even when you lock and shut power off ???????
 
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dtbaker61

dtbaker61

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Can you make the two 12 volt ports hot all the time ?
Even when you lock and shut power off ???????
I don't really know about the 12v ports.... they can only carry 15 amps at 12v. I haven't tested what it takes to leave them powered up when MME is off and locked.

I want to use the 12v battery connection points, and presuming that the MME has to be 'on' so that the HV battery dc-dc will keep the 12v battery charged when I am pulling juice out of it.
 

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Won't the HV batt charge when it is off ? I want to use the ports to
install LV batt monitor using the I Phone. If not I will have to remove
panels and connect directly to LV batt.
 

louibluey

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Won't the HV batt charge when it is off ? I want to use the ports to
install LV batt monitor using the I Phone. If not I will have to remove
panels and connect directly to LV batt.
The 12V outlets go off some minutes after the MME is off (very different from what Dan is doing). To monitor 12V when the car is off for hours, get an OBD power cable, connect to the LVB, or possibly take a tap from the small fuse panel in front of the front passenger's legs under the dash.

Search for threads on LVB monitor, OBD power, and dashcam installs for the various tap points. (we probably shouldn't hijack Dan's thread on a 120V AC inverter running on high current 12V power from the DC-DC converter).
 
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dtbaker61

dtbaker61

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Won't the HV batt charge when it is off ? I want to use the ports to
install LV batt monitor using the I Phone. If not I will have to remove
panels and connect directly to LV batt.
theoretically you should not have to monitor the 12v battery voltage. The MME is supposed to wake up and check periodically, and then the HV will charge the LVB if needed.

if you really want to add a monitor, there are cheap (less than $40) voltage monitors that you can wire directly to LVB connection points, and it will communicate via bluetooth (usually limited to 10 meters or so) to your phone once paired.

https://www.wish.com/product/5e22a99ad078380be17e77c9?

but, this has nothing to do with the ampacity of the HV to LV dc-dc converter that this thread is about..... ;)
 

ChasingCoral

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I want to use the 12v battery connection points, and presuming that the MME has to be 'on' so that the HV battery dc-dc will keep the 12v battery charged when I am pulling juice out of it.
theoretically you should not have to monitor the 12v battery voltage. The MME is supposed to wake up and check periodically, and then the HV will charge the LVB if needed.
You've contradicted yourself here. I think the latter is correct and you will not need to have the Mach E on to keep running 12v power off the battery access jump points and the dc-dc system should keep it topped up. There's only one way to find out for sure.

This would be different that doing this same operation on my Leaf. The Leaf definitely has to be turned on to keep the 12v battery topped up.

 

 
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