Clarity as a back-up power source? (DC-DC converter size, idle behavior)

Discussion in 'Clarity' started by M.M., Mar 31, 2018.

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  1. M.M.

    M.M. Active Member

    I just finished wiring my house with a transfer panel so I can put a few circuits on a UPS. As a Volt owner, I also figured, "hey, wouldn't it be cool to get, say, a 1000W 12V inverter, hook it to the 12V battery in my car, and use its nice big battery pack and quiet motor-generator in place of a generator?"

    In the case of the Volt (apart from relatively high parasitic power draw and it shutting down after 90 minutes), this works really well--the ~60A DC-DC converter will pull from the high voltage battery pack to keep the 12V battery full, and when the high voltage battery eventually runs down it will turn on the gasoline engine and use that for power. Bingo, 10+ kWh of stored energy, a gas generator that's way quieter than anything I could buy, and a big ol' portable fuel tank.

    Then of course I went and bought a Clarity almost immediately.

    Google was proving useless, so does anyone here have an idea of what the capacity of the DC-DC converter that feeds the 12V battery is, and how the Clarity behaves when in park (or neutral) with a high draw on the 12V battery?

    I've noticed that even in "eco" mode my Clarity will turn on the gasoline engine if I sit there in park listening to the radio for even a few minutes, which seems fantastically pointless and is tremendously annoying if I've got plenty of high voltage battery capacity left (seriously, the gas engine is noisy and I'm sitting on 15kWh of energy, why the heck are you turning on the engine?). Which leads me to believe that the car doesn't like to pull from the high voltage pack when "idling". Any concrete info on this?

    I'd also rather like to be able to disable that stupid "idle with full battery pack" misfeature, but I'm not holding my breath there.
    sabasc likes this.
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  3. KentuckyKen

    KentuckyKen Well-Known Member

    I haven’t noticed this in mine, but I’ve only sat in Park for less than 10 min. The manual does caution about running down the 12v battery, but doesn’t say what the car does in response.
    When this happened, we’re you in run or acces mode?
    Did you have any high current draw also going on like auto headlights on, or heating, etc.?
    I would expect that the 12v battery would power just the radio in acces mode for quite a while as in all ice cars I’ve had.
    Might want to check your 12v battery, even though it’s new. Could it not be charging or maintaining charge fully?
    This will be another interesting Clarity characteristic for us to figure out.
    And let us know if you find a way to turn the car into an emergency battery bank.
  4. M.M.

    M.M. Active Member

    Run mode. I've had it happen more than once; yesterday the car was in run (park gear), the outdoor temperature was probably 60F, it was light out so the headlights weren't on, and I was just messing with the entertainment system. It happened pretty quickly, too--it was definitely under five minutes.

    The only high-draw culprit I can think of would be the climate control, but the temperature was so moderate that neither the A/C nor heater should have been doing much if anything (it wasn't noticeable, at least, and this was after driving for a while, so the car should have been conditioned to whatever temperature it was set to by then).

    I'd assume one of the 12V battery warnings would have come on if the aux battery was DOA, but assuming the Clarity charges it off the main pack (which is not a given), it basically should be supplying all power from the DC-DC converter anyway, so unless the 12V battery was so toast it was sucking some huge amount of current at float/charge voltages it shouldn't matter.
  5. KentuckyKen

    KentuckyKen Well-Known Member

    Sounds as if the HV battery was not giving any charge to the 12v battery. But then why wasn’t the HV battery taking care of the climate control as it does in preconditioning, if that’s what was causing the high draw down?
    FWIW, in run mode in my driveway or in a drive through, I have seen the EV range drop a tenth or two over 5 min or more, but have never had any 12v battery problems or warnings but that was with no other non motive energy draws.
    So the question is, does the 12v battery charge off the HV battery or does it need the drive shaft spinning to generate charge??
    Sigh...Another Clarity riddle to solve.

    If you drive enough to fully charge the 12v battery and it won’t handle 5 min on run mode sitting still with no other non motive current draws than housekeeping and radio, then I’d have to say test your battery and/or take it in for service. It appears not to be acting as it should.
  6. M.M.

    M.M. Active Member

    This can't be true and wouldn't make sense. There is a pile of stuff that runs at 12V and would rapidly murder the 12V battery if it could only be charged off the ICE, and not only would it make bafflingly little sense to have a 12V generator somehow hooked to the wheels (substantially less efficient, more prone to failure, and more expensive to build than a DC-DC converter), that would just result in the ICE turning on right away if you were stuck in slow-moving traffic at night or with the A/C on.

    I'll put a meter on the 12V battery at some point to make sure its voltages make sense and experiment at some point with what's triggering the ICE to come on at idle.

    I can say this for the Clarity; as an almost-former Volt owner it has a lot of advantages, but the logic behind the EV/hybrid transitions and how it dispatches the ICE is both much more opaque and not nearly as logical.
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  8. KentuckyKen

    KentuckyKen Well-Known Member

    I absolutely agree with your logic. Obviously the 12v battery is being charged without ice running. I’ve done so for almost 1,000 miles. I was thinking more of a stop vs motion thing.
    Page 18 of manual says HV battery recharges the 12v battery which as you said makes a lot of sense.
    So how do we explain your ice coming on during run mode in park with good HV battery level? I could see it doing that once if it was doing the occasional System Check but not every time. I’m stumped. Definitely not how mine behaves.

    You do have me intrigued with thinking about that 13 or 14kWs of usable power sitting in my garage during the next power outage. I wish here was an easy way to tap into it.
  9. M.M.

    M.M. Active Member

    Well, if (and this is a big series of ifs) the DC-DC converter is sufficient, the charge controller is smart enough, the parasitic load in idle is low enough, it doesn't do anything wonky with the ICE until it has to, and it will stay on, it actually is pretty easy--just get a not-too-beefy inverter, clip it to the 12V battery terminals, put the car in park (or neutral with the parking brake on, depending), turn everything you can off, and you're good to go (minus parasitics).

    That was my plan with my Volt, though the parasitics are a bit high and you'd need to put it in neutral to keep from shutting off after 90 minutes.

    The microgrid engineer in me (it's my day job) says it would be really cool if the AC charger on the high voltage battery pack was bidirectional, and the J1772 charger had an extra set of contacts or something, such that when commanded the car would go from being a load to a power source. Add an ATS to the charger, and you've got 10-15kW of battery backup for whatever critical loads are on your ATS when the power goes out. If the parasitics were low, this would keep my fridge and some lights on for at least a couple of days without even needing the ICE.

    You could also modify the high voltage system with a high-voltage inverter to produce a similar effect, and it would be awesome to try, but I'm nowhere near wealthy enough to void my warranty trying.
  10. Gearhead

    Gearhead Member

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  11. M.M.

    M.M. Active Member

    I'm a little surprised I've never heard of that, but it's very cool.

    A PHEV or EV version would actually be simpler to build--it looks like that version has some kind of DC-DC converter upstream of the inverter to handle the wide voltage range on a fuel cell, but the voltage on a li-ion battery pack is virtually flat in the range that's actually used so there should be no problem driving an inverter directly off it. Leaving aside capacity management, really any high-DC-voltage inverter could plug more or less directly into the pack

    It's not going to be an option on current model PHEVs/EVs regardless, though, because it requires a point of DC connection to the li-ion battery pack, which does not exist on the current PHEV Clarity (unless there's a service port buried inside somewhere that one could be retrofitted onto).
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  13. ab13

    ab13 Active Member

    Here's what it says in the manual. It seems it has a very conservative battery protection system in place that the system computer is running. I gather it's because the previous hybrid systems had some battery issues that required full replacements. So they are going conservative this time to protect the functionality. There is probably a current draw range and duration with respect to the state of charge that kicks off the ICE.

    "Auto Engine Stop/Start
    The car will select the appropriate source of power depending on the drive mode you select.
    As a result, the engine will automatically start or stop as needed to either charge the battery or provide supplemental power.
    Under certain circumstances, the engine may turn on or, if it is already on, it may not turn off.
    ● You are going uphill or accelerating aggressively.
    ● The climate control system is in heavy use.
    ● The Ambient temperature is too hot or too cold.
    ● The High Voltage Battery state of charge is very low.
    ● The vehicle is running a system check."

    Also, it says, so the accessory power is limited in output.

    "The accessory power sockets are designed to supply
    power for 12-volt DC accessories that are rated 180
    watts (15 amps) or less."
    Last edited: Apr 1, 2018
  14. M.M.

    M.M. Active Member

    To be clear, that's regarding accessory power socket. The 12V "cigarette lighter" port under the dash. It has a 20A fuse on it. The total 12V accessory power can be substantially higher--the seat heaters probably draw 15A each, the rear window defroster is probably 30A, and so on. If you're being creative and pulling directly off the battery, you would presumably have disabled as many aux things as possible (climate control, seat heaters, sound system, etc), leaving more power for the intverter.
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  15. Gearhead

    Gearhead Member
    I suspect the Honda box is similar with one big difference; it won't void the warranty. I'd love this. The power output should be on the order of a medium sized Generac standby generator.
  16. M.M.

    M.M. Active Member

    I'd run across ConVerdant when checking options, and while they appear to be basically out of business, yeah, that's more or less the same thing. Their 1kW model is on the 12V system, but the 2-5kW "Islanding" versions are hooked directly into the high-voltage system.

    Of course, a 12V version shouldn't actually void your warranty, either, since it doesn't require anything to be cut or disconnected to function and could be removed without affecting the car, but you're losing efficiency from having to run through the DC-DC converter first, and the fact that 12V inverters are less efficient than high-voltage input ones.

    You could kludge together basically the same thing as this by just buying a 12V inverter and clamping it to the 12V battery one way or another (which is what I'm considering).
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  17. ab13

    ab13 Active Member

    I understood after looking at that again. I was indicating that they were not expecting any user accessory at high power. Maybe if the inverter had a slow initial current draw, or a current limiter then the range of power draw in EV mode the vehicle system allows could be determined.
  18. Gearhead

    Gearhead Member

    Yes, the 12V doesn't leave any fingerprints behind. Any concerns with excessive heat in the battery?
  19. M.M.

    M.M. Active Member

    Follow up to battery test questions: I put a meter on the 12V battery (it's the fanciest car battery I've ever seen) and did a few quick experiments. Battery was around 12.5V at open circuit, so its reasonably healthy and mostly charged. In accessory mode with the stereo on, it was a bit lower; as expected, and confirmation that the car doesn't use the high voltage battery in accessory mode (though it might shut down for safety at a certain level of 12V charge). With the car on and in park, the 12V battery was being held at a standard float voltage of 14.6V, give or take, even without the ICE running. When I turned on both seat heaters on high, cranked up the A/C, and also had the stereo on, the voltage only dropped a hair, confirming that the DC/DC converter can and will put out a fair amount of power.

    The only theory I have left on why my ICE turned on (it didn't during this short test) was that it was cold enough to require heat, and the system prefers to use the ICE for heat while idling, while it will, at least under the mild environmental conditions in my area, use the high voltage battery while driving in EV mode.
    Thing is, the 12V system is clearly designed for relatively high power draw, since on a cold night it can reasonably be expected to be running both front seat heaters, the cabin fan, the rear window heater, and the headlights all at the same time for potentially quite a while (tens of minutes, at least, in EV mode, many hours in hybrid mode). This is why I'm pretty confident that the DC-DC converter can supply quite a bit of power on the 12V bus.

    And the important part is that the power electronics have no idea where the 12V power is going, only the voltage on the bus, so if it can supply, say, 50A, it doesn't really care whether that 50A is going to the seat heaters and headlights, or an inverter when everything else is turned off. You could of course overload it and draw down the 12V battery if you slapped a loaded-down 1000W inverter on there in addition to a bunch of accessory stuff, but if you turn everything else off it's just going to look like it's a cold day to the car.

    For the 12V battery, none, because you shouldn't be using it except for brief spikes if the DC-DC converter is big enough. Per the above-mentioned test, it can put out at least a few hundred watts. At >14V there is no energy at all coming out of the 12V battery (actually, it's being charged slightly); everything is coming from the DC-DC converter. So the only extra heat in the 12V battery would be from charging it, not discharging it.

    If you meant the lithium ion battery, also not an issue, since it should have cooling built in, and 0.5-1.0kW is nowhere near the >10kW the car is using at cruising speed on the highway, let alone the >100kW it uses when accelerating or going uphill.
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  20. Hi.Ho.Silver

    Hi.Ho.Silver Active Member

    Interesting discussion. I'm thinking of buying a 1000-1500W inverter to have for emergency power outages that I could use to power our fridge and freezer alternately. Might even be able to use it for the gas furnace (blower). I wonder if the ICE would start-up to maintain or recharge the HV battery when it got low.
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  21. insightman

    insightman Well-Known Member Subscriber

    I may have missed someone else pointing this out, but that Exporter uses the hydrogen fuel cell in a Clarity Fuel Cell to generate electricity. A full load (both tanks) of hydrogen can power a small house for as long as a week.
  22. VancleVector

    VancleVector New Member

    My experience is that people want (a) easy and (b) I'll focus on portable units.
    Where are you going to (1) store your generator (2) set up the generator to use it? Remember, it may be severe weather so, where could you put it to keep it safe and be able to refuel it easily? If you're using power cords, will they be dry and as far out of the way as possible?
    Small generators (less than 5500 watts) can only do so much. If you overload the unit and damage it, you won't have any power at all. So be smart! Portable units are made up to almost 20k watts but they're not for people on budgets.
    The bottom line is to add up the load (watts) you plan to connect and size your generator set at least 25% higher. When motors like the compressor in the refrigerator start up there is a sudden draw of power higher than the normal running load and you want to compensate for that.
    Small appliances will have the wattage marked on them. Lighting circuits will be less than 1200 watts each. Water heater is 4500 watts alone.
    Also,you'll truly get what you pay for...unless you buy from one of those guys selling from the back of their pick-up truck (don't do that). Don't wait till the last minute or you'll be stuck with whatever is left in the stores.
    Oh, and the "trick" with connecting the generator to the dryer outlet to backfeed the house? DON'T YOU DARE!! It will result in damage and/or injury...
    Hope that helped a little...sorry it's so wordy
  23. samzilla3

    samzilla3 New Member

    Hey everyone. I have been considering putting a high power after market sound system in my Clarity, and I too was wondering how much the DC to DC can handle. My coworkers and I put a current loop probe on the negative terminal of the battery (see photo). We then turned on all the accessories we could while the car was in accessory mode. With the heated seats and rear defroster on, fans, high beams, etc, we were able to observe an 80 amp load on the battery. Then when we turned on the car and the current changed polarity and started charging the battery at 70 amps (then slowly started tapering down as the 12V battery recharged)... with all accessories still going. So that was at least a 150A delta the DC to DC was driving, or around 2KW. Also, I have a feeling additional 12V accessories came on when turning the car fully on to put additional load on the DC to DC we didn't see in accessory mode, such as AC (it says it was on in accessory mode but no cold air was coming through) and the power steering. But I am uncertain if these are on the 12V bus or the high voltage battery.

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