Designing car system for road tripping/camping - 12V or 24V?

[mikefitz]

12v 'stuff' is available everywhere including LA 12V batteries. If something goes wrong on the vehicle charging system the service battery and solar can be rigged to power the vehicle. If the service battery system fails the engine battery can be used tempory to power critical loads.
It's unlikely you will find a 24 volt battery to fit your limited space.
I would be concerned that it may be possible, due to item failure, design mistakes, wiring errors or equipment connected to both vehicle and service power, to inject 24 volts into the vehicle electrical system.

General comments, 12/24 volt hair driers and kettles are useless.
Battery monitoring , Smart Shunt or similar is useful.
Storing additional 300 watts of panel sounds impractical.
Mike

 

[Atom Tan]

This has all been super helpful, and I have enjoyed the practical perspectives. @mikefitz, I appreciate your component suggestions, and your tacit suggestion that I'm over thinking this.

My new load inventory is as follows:

Planned Loads: 1093 Wh/day

• Critical - 864Wh:
  • Dometic CFX3 75DZ fridge
    • Estimating a pessimistic draw of 36W/hr for 864 Wh/day
    • True worst case load around 60W/hr for 1440 Wh/day
    • I’m planning to put a logging meter on this load so that I can get a longitudinal sense of actual consumption, but that’s not helping me right now.
    • I'm still VERY pessimistic about this one until I have more longitudinal data to work with.
• Important - 229Wh:
  • 2 laptops, 58 Wh capacity, once each day: 139.2 Wh (58Wh derated by 20% to account for losses)
  • 2 phones, 10 Wh capacity, once each day: 24 Wh (10 Wh derated by 20% to account for losses)
  • 1 Bluetooth speaker, 20 Wh capacity, once every 3 days: 7.92 Wh (derated, etc)
  • 1 Hair dryer, 1000W AC, Inverter, 170Wh twice a week: 58.2 Wh/day (yeah, I know, not the right way to account for this since the usage will not be evenly spread across all days)
• Optional/Occasional:
  • DC Fans - USB-charged/battery powered or direct DC powered
  • USB-charged LED lights
  • Viair compressor (as needed)
  • All of these are basically noise at this point.

The laptops are still a bit pessimistic. Unlikely that BOTH will need a full charge each day, so that's some margin.

I still REALLY like the idea of multiple days of runtime without sun.

So, if I actually do burn 1093 Wh/day, I can get that back in just under 6 hours of sun, assuming a 330W panel derated by 40% as someone suggested. That seems feasible, especially if augmented by alternator or shore. If y'all are right that my Dometic load is too pessimistic, then the situation only improves.

Might just start out with a 1200 Wh 12V battery and see how it goes. I can always change or augment the battery later if it ends up being too small.

 

[Ramlanta]

I don’t know about your Dometic fridge, but my ARB fridge only spends about 20-30 minutes per hour using the compressor. This is in 95 degree heat and with the temp set at 35 degrees. Admittedly, it is ping ponging between 26 and 43 degrees, but it’s only running half the time or less. Also, it’s largely empty at the moment. It runs less when full of food and drinks. Consider buying a SensorPush or Govee sensor to check how often it turns on and off when full.

 

[mikefitz]

Your fridge is a small compressor cool box, typically it will consume less than 400 watt hours per day with normal use.

Total of your other loads, my guess 200 watt hours per day average

To reduce consumption further optional Insulating 'jackets' can be used on the cool box

You will have no difficulty meeting demand with 300 watts of solar.

I can see no problem with a single 100Ah lithium and careful management.

The fast charging of a lithium setup is a game changer for small RV systems.

Mike

 

[No Idea]

If you go the ammo box battery route so it still fits behind a seat i am pretty sure you can fit close to 200ah 12v plus BMS and wiring, fuses, etc depending on which brand of cells you buy and carefully getting the correct internal dimensions of the ammo box before you buy everything. My 8 x 50Ah cells use about half the volume of my plastic box. Or look at tool boxes for a better fit.

Just accept your DC DC charger has to be seperate either bolted down somewhere or loose and plug into an anderson plug tucked under the dash or something, same for inverter being loose too. maybe even the multiple PD/USB all in a seperate box. All a bit too big to fit together in one box and still behind a seat if 200Ah.

Please don't forget proper restraints for that box, your fridge, etc. It's the heavy stuff flying around inside your car in a bump will get you.

I used my seat runners existing rear bolts and added L brackets and used those as attachment points when I was off roading. My small dometic fridge was behind one seat (no LFP back then).

 

[Zwy]

I generally agree with the 2000 watt inverter suggestions, but I also think you could get by with a 1500 watt.

I think you have greatly overestimated your loads.

Your "critical load", instead of 864 watt hours per day, might be closer to 250. Link

2 phones 10 watt hours
2 tablets 60 watt hours
2 laptops 80 watt hours
hair dryer 175 watt hours
electric kettle 175 watt hours

So, instead of 1240 watt hours for your "important loads", maybe 500 is more realistic?

That's just 750 watt hours. Add 100 for a fudge factor and you are at 850. That's a lot less than your number of 2104.

Does that make the 12 volt Battleborn battery solution more attractive? Two 100 amp hour Battleborn batteries should power a 2000 watt inverter okay.

Your charging loads refrigerator and lighting loads can bypass the inverter, so no inverter efficiency losses for them.

The only thing that I see you gaining by going to 24 volt is smaller wires from the battery to the inverter. Seems that would only be important if the inverter was a long way from the batteries.

Not necessarily. Watts are watts. 1200W on 12V would be a load of 100A thru a BMS. On 24V, the same 1200W load is 50A thru the BMS.

This is why you see people "left in the dark" when a larger load is put on a 12V system, the BMS is only rated at 100A.

I think your bigger problem is going to be charging, and from that perspective the bigger the battery, the better, allowing you more autonomy between shore power charges.

 

[Atom Tan]

I think I'm going to stick with off the shelf batteries for now. Building my own pack is a deeper rabbit hole than I want right now.

So I'm looking at options. Way I see it, I can either start small with a 12V 100Ah battery and see how it goes, or try to maximize my battery capacity out of the gate. I know I want a heated/low temp protected battery, because we will be traveling in the winter.

If I start small, I can either buy any decent quality battery that'll fit in the footwell (19" wide x 10.75" deep), which will be just about anything in the 100Ah range, or I can try to buy a battery sized and shaped such that a second identical battery will fit next to it in the footwell in the future.

If I just go with anything decent that fits, I'll have to pull that battery out and replace it with something else if I need more capacity. That's not the end of the world, as I'm sure I'll find a use for it, but it's (potentially) the most expensive option.

If I try to size for a second identical battery, I seem to be constrained to GC form factor batteries, of which I have found only BattleBorn. They look like great batteries, but I'm not sure the premium is worth it. Of course, if they're the only game in town for the GC form factor, then so be it.

I'd be looking at about $1k for one heated BB battery, or $2k for two. A 12V 100Ah heated battery from CHINS is $550 and is close to $700 from AmpereTime.

One BB GC battery leaves a TON of room in the footwell for components.

Two BB GC batteries will leave a roughly 4" wide and 10.5" deep space open on one side for other components.

If I start large, I have a couple of options, of which the Kilovault 2400 HLX+ seems most attractive. I think I can make it fit in the footwell by elevating it an inch or so (footwell walls get further apart as you go up), and it will leave roughly a 19" wide and 4" deep space open front to back in the footwell for other components, like the inverter, SCC, etc.

The Kilovault is $1500 or so.

So, my basic calculus now is twofold:
1. Do I start small and risk spending an extra $500-$1000 over what I'd spend on starting large?
2. What is the value of the additional footwell space offered by either option?

I'm leaning towards the Kilovault.

 

[Atom Tan]

I ended up looking seriously at 5 possibilities and bought the SOK 206Ah heated battery.

I looked at these:

Manufacturer/Model	Spec	Cost per Wh
BattleBorn BBGC2H-1KIT	12V 100Ah (1200 Wh) Heated GC2 Size	$0.83/Wh
Discover DLP-GC2-12V	12V 120Ah (1536 Wh) Heated GC2 Size	$0.85/Wh
Relion 12V120-GC2-LT	12V 120Ah (1536 Wh) Heated GC2 Size	$0.94/Wh
Kilovault 2400 HLX+	12V 200Ah (2400 Wh) Heated 19.9"Lx6.77"Wx10.x"H	$0.60/Wh
SOK SK12V206H	12V 206Ah (2636 Wh) Heated 12.9"Lx7.9"Wx12.3"H	$0.46/Wh

For a long while, I was leaning strongly to the Relion, because I really liked what I saw in terms of construction, quality, and features. I liked the CANBus communication among and between batteries. It was also the most expensive at $1495 each, and cost would double if I needed more capacity. But two would fit in the footwell.

The BattleBorn was the "simple reliable choice", in that I knew it'd work, and the quality is a known quantity. Two would fit in the footwell if I needed more capacity.

The Discover isn't available yet.

The Kilovault looks like a very nice battery, and checks all the boxes, except for fit, and it's close there. I like the 150A discharge/charge rates, and like the UL certifications and the overall reliability. I could make it fit with some work. But end of the day, the siren call of more capacity for less money lured me away.

I was surprised that the SOK ended up being the dark horse winner. I'd eliminated SOK from consideration initially due to reservations about the BMS's charge rate, but added it back as I learned more.

It ended up being my choice for several reasons.

• It's compact. It's not GC2 sized, but it's smaller than 2 GC2 batteries and has more capacity than 2 BattleBorns. If 2600 Wh isn't enough capacity, then the extra 436 Wh gained from paralleling two Relions probably isn't going to be enough either.
• It's heated.
• It's a metal case, which I think will contribute a bit to safety.
• It's also relatively inexpensive at $1200.

My only reservation is the BMS. 100A continuous discharge is slightly below the max service amps (101A) I calculated for my inverter. I'm hoping that the headroom between 100A continuous and the 200A for 3 second peak discharge rate will be sufficient. The 50A max charge rate isn't an issue, since I'll be hard pressed to put 50A into this battery at any point. In full sun with shore power charging, I'd still be lucky to hit 50A.

If it turns out to be a poor choice for the car, then I can pull it out and use it for another power station and get something else that better fits my hopefully-then-better-defined real world needs.

 

[cs1234]

If you have your DC to DC charger running while you exceed your continuous battery discharge rate, I think that should be able to be added to your overall amperage to some degree. That might help with your biggest loads, just turn the car and DC to DC charger on. You likely wouldn't be using a DC to DC charger with more than 15-40 amps of charging, but it might help.

If you don't mind pulling even more charge from your alternator and your 12v starter battery, you could use an additional (second or third) DC to DC charger that you flip on when you need even more amperage, just be sure to not be running your headlights, super huge car stereo and other 12v loads built into the car. Be sure to stay under a combined tested/known limit of what the fuses in your 12v car system will allow, don't want to blow them out.

 

[12VoltInstalls]

Since the only load you absolutely have to use on inverter is the hairdryer you migh be able to get by with modified sine wave inverter.

For the difference in cost and the likelihood of burning out the motor I’d not bother even considering modified sine wave. My modified experience was way more expensive than just buying a pure sine to begin with.

 

[Atom Tan]

For the difference in cost and the likelihood of burning out the motor I’d not bother even considering modified sine wave. My modified experience was way more expensive than just buying a pure sine to begin with.

I'm never buying anything but pure sine at this point.

 

[magua]

I ended up looking seriously at 5 possibilities and bought the SOK 206Ah heated battery.

I looked at these:

Manufacturer/Model	Spec	Cost per Wh
BattleBorn BBGC2H-1KIT	12V 100Ah (1200 Wh) Heated GC2 Size	$0.83/Wh
Discover DLP-GC2-12V	12V 120Ah (1536 Wh) Heated GC2 Size	$0.85/Wh
Relion 12V120-GC2-LT	12V 120Ah (1536 Wh) Heated GC2 Size	$0.94/Wh
Kilovault 2400 HLX+	12V 200Ah (2400 Wh) Heated 19.9"Lx6.77"Wx10.x"H	$0.60/Wh
SOK SK12V206H	12V 206Ah (2636 Wh) Heated 12.9"Lx7.9"Wx12.3"H	$0.46/Wh

For a long while, I was leaning strongly to the Relion, because I really liked what I saw in terms of construction, quality, and features. I liked the CANBus communication among and between batteries. It was also the most expensive at $1495 each, and cost would double if I needed more capacity. But two would fit in the footwell.

The BattleBorn was the "simple reliable choice", in that I knew it'd work, and the quality is a known quantity. Two would fit in the footwell if I needed more capacity.

The Discover isn't available yet.

The Kilovault looks like a very nice battery, and checks all the boxes, except for fit, and it's close there. I like the 150A discharge/charge rates, and like the UL certifications and the overall reliability. I could make it fit with some work. But end of the day, the siren call of more capacity for less money lured me away.

I was surprised that the SOK ended up being the dark horse winner. I'd eliminated SOK from consideration initially due to reservations about the BMS's charge rate, but added it back as I learned more.

It ended up being my choice for several reasons.

• It's compact. It's not GC2 sized, but it's smaller than 2 GC2 batteries and has more capacity than 2 BattleBorns. If 2600 Wh isn't enough capacity, then the extra 436 Wh gained from paralleling two Relions probably isn't going to be enough either.
• It's heated.
• It's a metal case, which I think will contribute a bit to safety.
• It's also relatively inexpensive at $1200.

My only reservation is the BMS. 100A continuous discharge is slightly below the max service amps (101A) I calculated for my inverter. I'm hoping that the headroom between 100A continuous and the 200A for 3 second peak discharge rate will be sufficient. The 50A max charge rate isn't an issue, since I'll be hard pressed to put 50A into this battery at any point. In full sun with shore power charging, I'd still be lucky to hit 50A.

If it turns out to be a poor choice for the car, then I can pull it out and use it for another power station and get something else that better fits my hopefully-then-better-defined real world needs.

SOK has my interest for a particular application. Newbie to all of this. Do you know if I can connect 2 of these in series to trick my Ecoflow Wave A/C into thinking it's being charged from the solar connection?

Thanks

 

[cs1234]

SOK has my interest for a particular application. Newbie to all of this. Do you know if I can connect 2 of these in series to trick my Ecoflow Wave A/C into thinking it's being charged from the solar connection?

Thanks

I believe this works for most of the "solar generators".

 

[magua]

I believe this works for most of the "solar generators".

I need to run 2 of the SOKs in series for 24v and use that connector that has an angular form to connect to the EcoFlow Wave Solar Input.

 

[cs1234]

I need to run 2 of the SOKs in series for 24v and use that connector that has an angular form to connect to the EcoFlow Wave Solar Input.

I'm pretty sure there are youtube videos of people hooking up batteries to Ecoflows, give em a watch.

 

[12VoltInstalls]

I'm pretty sure there are youtube videos of people hooking up batteries to Ecoflows, give em a watch.

And then we’re at my question- “why not just use decent batteries and an inverter to begin with rather than spend so much money for so little capacity?”

 

[cs1234]

And then we’re at my question- “why not just use decent batteries and an inverter to begin with rather than spend so much money for so little capacity?”

It's ok to like both custom built systems and well packaged commercial products that look nice but can't be customized as much to your exact specifications. It's also cool to try and eek out a bit more usefulness from stuff you have laying around, which using batteries from a custom system or that you have extra to charge an ecoflow would fall under.

I like a wall or dolly loaded up with different components and wires hanging all over more than the average person, but I can also be lured in by a pretty package, ask my wife.

 

[Atom Tan]

Regarding the accuracy of my critical load estimate, now that I have a big enough battery (206Ah SOK), I did an initial test.

Conditions
I set the Dometic to 37F on one side and 5F on the other side, and let it come down to set point temp before beginning the test.
I put nothing in it, so this is in some ways a worst case condition maintaining temp in an empty vessel.
Ambient temp was between 79F and 82F for the duration of the test.
I left it entirely alone, no opening or closing of the lid.
I have a Victron BMV-712 monitoring SoC and current consumption via the provided shunt. SoC is probably a bit off, but I'm relying on current consumption which should be very accurate.

Results
At 57.3 hours of runtime, the Dometic had drawn 146.8 Ah. That works out to 30.7 Wh/hr or 737.6 Wh/day using 12V as the voltage to do the conversion between Ah and Wh.
I'm presently down to about 20% SoC based on under-load voltage, and 28.7% SoC based on nominal capacity less consumed energy.

The Dometic did a solid job keeping the 37F temp, and was consistently holding at 7F on the 5F set point.

My next test will be to fill it with mass, bring it to set point temp, and see how that goes.

Update
At 60 hours of runtime, the Dometic had drawn 150 Ah exactly. That's 2.5 Ah/hr or 30 Wh/hr, and 60 Ah/day or 720 Wh/day.

 

[Atom Tan]

This thing is STILL GOING. We are at 77 hours of continuous runtime, 194.5 Ah consumed, and an estimated 5% or so capacity remaining based on that consumption figure.

Running to 20% SoC as a discharge floor should easily net 60 hours of runtime without charging. That should be PLENTY of margin, and it should only improve in the next test, as I fill the Dometic with mass.