Electric Draws

I’m doing my calculations for the electrical systems for the CC.  What are you using as a roof fan?  Did you use the existing roof vent opening?

What wattage did you estimate for the house lights?  I’m thinking 8 hours a day would be overkill as a planning factor.

Current battery is 220 watt agm.  No solar but I may go with higher amp alternator instead.  Goal is to go 5 days. Fridge draws 44 watts, cpap 2.2-4.3 amps, plus 2 iPads and 2 iPhones.

Thoughts!

It all depends on what you are doing, if you charge your i pads and phones and keep the fridge running as you drive then you can take a lot of their power usage out of the equation because they're fully charged and the fridge is very cold. Unless you keep opening the fridge it can stay pretty cold with the odd blast every now and then.

But I don't think it's got anything to do with your alternator power all that does is charges the battery faster. Without solar the power you have to use when parked depends only on your battery because that's where it's coming from and bear in mind that AGM batteries lose voltage as they lose charge.

To calculate if you have enough you divide the watts used in a day by twelve (12V system ) and your battery's amp hours has to equal it or be better.

For example your fridge is 44Watts you use it for 4 hours that is 44 x 4 which equals 176watt hours divided by 12V =14.6ah With that calculation a 120ah battery you could run your fridge for over thirty hours but as it hits 50% power the voltage drops below 12.

amps = watts divided by volts, volts = watts divided by amps and watts = amps x volts, knowing the wattage of your battery isn't much use it's the ah that you want to look at. Which I suspect is what the 200 of your battery is because if it's watts that's not a very powerful battery. 200w/12v = 16.6a, just over four hours with your fridge and you've got a flat battery.

I just have the ceiling vent and also a usb fan... But what is this cpap that is 90 watts ?

Hello West Coast Hiace CC and welcome to the forum

NickZ is spot on as ‘it depends’.

There topic of camper leisure electrics is vast and you can spend as much as you can afford and then some putting a system togerther. The Australians are probably the best kitted out for this for the somewhat nomadic and the Americans for the RV systems.

It sounds like you have a fairly standard set of requirements but as NickZ says there are lots of options and variants.

My advice would be to look at the many YT vids and themes out there and a good place to start might be this:



but Greg has several excellent vids and this will also set you down loads of hopefully fruitful rabbit holes.

I’d suggest a few things
• AGM batteries can only be discharged to ~50% before they struggle and their long term performance degrades. Lithium has a much greater discharge capacity and is lighter but more expensive and needs more modern technology.
• Duty cycle is everything for ‘always on’ systems such as fridges. I have plots somewhere showing the current draw at different internal settings and ambient temps for a 12V Engel fridge. It’s not quite the same model that’s fitted to CCs but it’s useful, if I can find it again. Assuming I do, I’ll add it to the long first post on my show us yours section. The post, which has loads of handy resources etc, might be useful to you in any case. Do take a look (another CC anyhow).
• I think it’s almost impossible to maintain electrical systems in an off-grid way (several days) without solar or driving or both without going unnecessarily mad with battery storage or additional packs (powerbanks).
• Diesel heating has a big electrical draw (~10A at 12V) during start up.
• Gas cooking is a lot simpler than electrical (induction) but gas storage is not always straightforward.
• LED lighting is a no-brainer when off-grid. Every Watt counts and monitoring is really important.
• Off-grid mains supply in a van is somewhat expensive to implement. Don’t add if you don’t need or don’t build in more than you need.
• Mains hook-up is useful if that’s your thing but it also adds complexity, cost and needs careful and safe planning.
• You can’t beat physics but there are lots of new developments. Consider whether you want a permanently fitted system or could use a powerbank, which might have more flexibility.

Good luck!!

Lithium needs a B2B charger and it's a pain in the &%$* to ship your van when it becomes "hazardous" ! There have been too many fires on transporters caused by electric cars and lithium leisure batteries got dragged into the equation.. Totally unjust and expensive !

NickZ wrote:

It all depends on what you are doing, if you charge your i pads and phones and keep the fridge running as you drive then you can take a lot of their power usage out of the equation because they're fully charged and the fridge is very cold. Unless you keep opening the fridge it can stay pretty cold with the odd blast every now and then.

But I don't think it's got anything to do with your alternator power all that does is charges the battery faster. Without solar the power you have to use when parked depends only on your battery because that's where it's coming from and bear in mind that AGM batteries lose voltage as they lose charge.

To calculate if you have enough you divide the watts used in a day by twelve (12V system ) and your battery's amp hours has to equal it or be better.

For example your fridge is 44Watts you use it for 4 hours that is 44 x 4 which equals 176watt hours divided by 12V =14.6ah With that calculation a 120ah battery you could run your fridge for over thirty hours but as it hits 50% power the voltage drops below 12.

amps = watts divided by volts, volts = watts divided by amps and watts = amps x volts, knowing the wattage of your battery isn't much use it's the ah that you want to look at. Which I suspect is what the 200 of your battery is because if it's watts that's not a very powerful battery. 200w/12v = 16.6a, just over four hours with your fridge and you've got a flat battery.

I just have the ceiling vent and also a usb fan... But what is this cpap that is 90 watts ?

Cpap is for sleep apnea. 90-100 watts would be a peak. 52 is the average.

West Coast Hiace CC wrote:

Cpap is for sleep apnea. 90-100 watts would be a peak. 52 is the average.

Hello West Coast Hiace CC

I've found and added the graphs I have on the Engel fridges to my Show Us Yours section.

In a nutshell though 52W average is a fairly big load to run from 12V batteries. It's probably the biggest leisure draw in your van, if you've installed LED lighting etc. My fridge draws 44W and if you see the plots there it has to be very warm for this to have a 100% duty cycle.

52W is about 35Ah so you'd need ~70Ah AGM battery (absolute minimum) to run the cpap for 8h. AGM or other lead batteries can only safely dischage to 50% otherwise thier performance will degrage. With lithium you could just about manage with a 40Ah battery but that would also be an absolute minimum.

If you're looking to augment or upgrade the leisure electrics I'd suggest the cpap load needs a reasonable safety factor.

Good look!