Car Fridge or Freezer

[dylanpete]

Is it correct that the BMW i3 REx will operate while the car is standing if needed to maintain the ~6% minimum charge state?
The point is that for professional reasons I normally have small fridge and a freezer in my car getting their juice from the 12 Volt outlets and I wouldn't like to see it shut down once I park the car and lock it. Neither would I like to see the 12V battery depleted or abused.
Anyone has experience with operation of car fridges / freezers in a BMW i3? Thanks in advance for your suggestions.

 

[mindmachine]

Is it correct that the BMW i3 REx will operate while the car is standing if needed to maintain the ~6% minimum charge state?
The point is that for professional reasons I normally have small fridge and a freezer in my car getting their juice from the 12 Volt outlets and I wouldn't like to see it shut down once I park the car and lock it. Neither would I like to see the 12V battery depleted or abused.
Anyone has experience with operation of car fridges / freezers in a BMW i3? Thanks in advance for your suggestions.

I don't believe the 12 volt will feed something like that very long before going dead, as the 12 volt is only rated at 20 amp/hrs.
I am not sure I would want to leave the car running or even if that would work out doing what you need as I am told the 12 volt is recharged only (?) while the high voltage traction battery is being recharged. Also some members on here are having 12 volt battery issues already.

 

[I33t]

A solution would be to install a portable rechargeable battery of adequate size to run your fridge for the duration of your trips. These are becoming common for camping and could run for quite a few hours depending on the size and current draw of your fridge.

We use a 60AH battery on our outback trips (not in an i3 lol) and we get plenty of hours out of it without drawing from the main battery. The alternator charges the battery when the engine is running though, so it works forever as long as we run the vehicle every day or so.

To maintain the range of the i3 and the life of its piddly 12v battery I suggest the fridge and battery be run independent of the i3. Pull the fridge battery when you get back home or to your overnight stop and put it on charge.

 

[jadnashuanh]

To be sure, I'd have to go back and read the owner's manual, but I seem to remember that the 12vdc sockets are quite limited - 2A max. Fine for recharging a phone or something, but marginal for most things like a portable frig. I'm kind of surprised it supports the mobility kit (compressor), but I've not run it, and it may be quite slow and not draw as much as some others I'd dealt with.

The on-board 12vdc battery is only maintained while recharging the main batteries, or while the vehicle is in the ready state...otherwise, the 12vdc battery is not fed by the main batteries (it gets charged by a dc-dc power supply, and that doesn't run unless the car is essentially on or being recharged by the cord).

 

[dylanpete]

A sincere thanks for your answers and sharing of experience.
I also received an answer from a BMW rep that each 12 Volt socket can provide 140 Watt and as long as the power draw from the fridge or freezer stays safely below that figure we would be doing OK. According the same representative, when the car is parked, the drive battery will continue to supply power to the 12 V on board battery but this has the inherent risk of discharging the main battery and consequently it would be up to me to integrate a technical solution to prevent this from happening.

I have asked BMW if it would be possible to piggy-back a second compacter Li-ion battery to the inverter system that charges the on board 12 V battery from the main drive battery.
My idea is to avoid cycling the 12V on board battery and to avoid any stress on the on board 12V circuit.
I guess it will depend on the specs of the on board inverter system and if a piggy back connection is easy to install...?

 

[ultraturtle]

I would recommend against powering any accessories from the 12 volt car outlet.

Bottom line is that it has the potential to brick the i3 far more easily any ICE vehicle you have had experience with. The i3 (like all EVs) has a tiny 12 volt battery meant only to maintain enough charge to boot up the computer (think coin battery in early PCs) enough to wake up the traction battery which powers the buck converter to charge the 12 volt battery as well as maintain the tiny draw of the always-on cell phone and key fob connections. From page 39 of the General Vehicle Electronics document:

In contrast to a vehicle with a combustion engine, the requirements of the 12 V battery in the I01 with regard to an engine start are different. In the I01 the job of the 12 V battery is only to ensure the powering up of the high-voltage system. What is required of the 12 V battery is no longer a minimum SOC to ensure engine starting, but rather a minimum SOC to protect the 12 V battery against freezing at temperatures below 0°C and to power up the high-voltage system.

The voltage supply of the 12 V vehicle electrical system (and also the charging of the12 V battery) is not provided by the conventional alternator, but via the DC/DC converter in the EME.

The i3 12 volt battery only has a 20 ah capacity, as opposed to the 70-90 ah typical of ICE (cranking) batteries you are accustomed to tap powering your refrigerator and freezer. The capacity reduction makes sense, as there is no need for the massive cold cranking amp requirements that increase the size and total energy storage capacity of ICE vehicle batteries.

I would recommend an entirely different approach as suggested by I33t. Power the refrigerator and freezer loads from an independent power source that you plug in and recharge on the same interval you do your car. I currently do exactly that with a 4.8 kWh battery based power unit that I use to double my other EV's range on a daily basis, and it entails only the additional inconvenience of plugging in an additional cord every night when I plug in my EVSE anyway.

Your needs are more modest, and (assuming 2 x 2 amp loads for both the refrigerator and freezer) could be powered for 8 hours, (adding a 72% reserve capacity - another 6 hours) with a single 55 aH AGM battery like the Optima Yellow Top 8014-045-FFP for ~$198 on Amazon:

 

[Chrisn]

Will the car stay "on" if you put in "P", exit car and lock doors? In which case (with A/C, lights and radio off), the High Voltage battery and DCC converter should provide the power for 12V accessories, right? That's how it worked in the Chevy Volt. Prob wastes some SOC from keeping the car in "READY," but perhaps not too bad....

 

[dylanpete]

I would recommend an entirely different approach as suggested by I33t. Power the refrigerator and freezer loads from an independent power source that you plug in and recharge on the same interval you do your car. I currently do exactly that with a 4.8 kWh battery based power unit that I use to double my other EV's range on a daily basis, and it entails only the additional inconvenience of plugging in an additional cord every night when I plug in my EVSE anyway.

Your needs are more modest, and (assuming 2 x 2 amp loads for both the refrigerator and freezer) could be powered for 8 hours, (adding a 72% reserve capacity - another 6 hours) with a single 55 aH AGM battery like the Optima Yellow Top 8014-045-FFP for ~$198 on Amazon:

Thanks ultraturtle for your detailed and well thought response, I appreciate it!
I will follow your and I33t's advice and intend to use an additional battery to cope with the needs of the car fridge / freezer.

 

[jadnashuanh]

The 12vdc battery only gets charged when the high voltage system is on, and that's only when you are recharging the vehicle or you are in the 'READY' state. IOW, it will not recharge the 12vdc battery normally when the vehicle is 'off'.

 

[Chrisn]

The 12vdc battery only gets charged when the high voltage system is on, and that's only when you are recharging the vehicle or you are in the 'READY' state. IOW, it will not recharge the 12vdc battery normally when the vehicle is 'off'.

I get that. But if you can leave the car "on"/ READY while in P and parking brake on but with doors locked, this could be a better solution than lugging a heavy additional battery around. This would be true only if the range was still sufficient even after accounting for the power needed to run the fridge.

 

[ultraturtle]

...if you can leave the car "on"/ READY while in P and parking brake on but with doors locked, this could be a better solution than lugging a heavy additional battery around. This would be true only if the range was still sufficient even after accounting for the power needed to run the fridge.

Good trick, but a bad idea in my opinion.

To your point, range remaining is insignificant to the question at hand. Even an 8 hour load (assuming the OP uses highly efficient 2 amp refrigerators and freezers) would draw less than 400 wH or ~ 2% of the i3 useable capacity. The buck converter itself (2.5kW capacity) is immensely capable (by a factor of 50x) of supplying the 48W load (see page 62 of the High Voltage Components document). Problem sorts out to the practicallity of running that massive a system to power such a small draw.

Adding the weight of a 43 lb battery to power the devices would theoretically increase electrical energy drive consumption by roughly 0.74%, or less than $23.50 over the course of 100,000 miles of driving (assuming $0.11 per kWh) to carry the extra weight. Totally worth it, in my opinion, to avoid stressing the BMW i3 12 volt system componentry.