diy solar

diy solar

12V vs 24 volt

Freddmc

New Member
Joined
Sep 29, 2019
Messages
123
Location
Vancouver ,B.C. Canada
My motorhome is all 12 volts.Is there any advantage (ignoring weight and size) to using one 200AH 24 volt battery and step it down to 12 volts or use 2 100AH batteries. Is there an efficiency loss going from 24v to 12v?

Thx
 
Using a step down converter in front of an inverter is not practical.
Do you plan on using an inverter?
If yes, which one exactly?
 
Is there any advantage (ignoring weight and size) to using one 200AH 24 volt battery and step it down to 12 volts or use 2 100AH batteries.
To me it is a question of the nature and size of the loads. There is some small loss stepping down 24 volts DC to 12 volts DC. However if most of your loads are AC there may be efficiencies in using a 24 volt inverter. It all depends on your use case.
EDIT:
..and, as noted below, your charging sources.
 
Last edited:
The big advantage of going with 24v or 48v is the watt/hours you can squeeze from a dedicated alternator. Otherwise you’re just saving a few pounds of weight by using smaller cables.

If you’re not going to have a second alternator, I don’t think a 24v system makes much sense.
 
Last edited:
The big advantage of going with 24v or 48v is the watt/hours you can squeeze from a dedicated alternator.
Please explain, not quite following.
If you’re not going to have a second alternator, I don my think a 24v system makes much sense.
Depends on the size of the inverter.
If the inverter is >2000 watts I suggest 24 volts system and a buck converter to supply the legacy electrics.
Unless they have high draw loads like jacks and/or levelers.
Then the decision is not so cut and dried.
 
Yes How do you plan to charge the 24 volt battery?
 
Please explain, not quite following.

Depends on the size of the inverter.
If the inverter is >2000 watts I suggest 24 volts system and a buck converter to supply the legacy electrics.
Unless they have high draw loads like jacks and/or levelers.
Then the decision is not so cut and dried.
Answering the first part, alternators are basically current limited, not power limited (pulley and belt size not withstanding) so if you have an alternator that can produce 100A continuously, the higher you set your voltage regulator, the more charging power you generate from your alternator.

As for large inverters with low input voltages, I would concede that there are safety issues associated with trying to extinguish an arc when a fuse blows as well as heating concerns if you have corrosion on one of your terminals, or a cable works loose. But I don’t see those as deal breakers.

Assuming you have a good crimper, torque all your fasteners, and use high quality fuses/breakers, the safety concerns with a 12v system can be managed.

On my RV nearly all my loads outside the AC and microwave are 12v. I’ve got a power management device that turns off the AC when the microwave is running so I don’t need a massive inverter pulling 250A. If I did need to run more than 2kw on a 12v system, I would likely install multiple inverters.

In my current RV, any wiring costs I might save going to a 24v system would be offset by having to include buck converters for all my DC loads. And since inverter standby power is generally a function of current, higher voltage inverters also have a higher baseline power draw which can be critical when boonfocking.

My next RV build won’t be an upgraded commercial RV but will instead be built from scratch and have a higher voltage system. I will install a second alternator at 24 or 48 volts so I can get additional charging while on the road and can eliminate the need for a generator.

I love desert camping where you never see a shadow or get any shading on your solar panels but I equally love boondocking in forested areas of Canada where the sun is low, the trees are tall, and outside of a few weeks in July and August, flat mounted solar on the roof is inadequate.
 
Last edited:
Answering the first part, alternators are basically current limited, not power limited (pulley and belt size not withstanding) so if you have an alternator that can produce 100A continuously, the higher you set your voltage regulator, the more charging power you generate from your alternator.
I was confused because @Freddmc didn't mention anything about alternator charging.
 
  • Like
Reactions: LB3
My motorhome is all 12 volts.Is there any advantage (ignoring weight and size) to using one 200AH 24 volt battery and step it down to 12 volts or use 2 100AH batteries. Is there an efficiency loss going from 24v to 12v?

Thx
Do you have slide outs? They tend to be high amp. It can be tough finding a sufficient 24V-12V DC-DC converter that can handle the high amps. Though you can put 2 converters in parallel to get higher amps if needed.
 
Yes How do you plan to charge the 24 volt battery?
With solar, alternator, and a battery charger, they come in 24-volt too.

They make 12to 24-volt DC to DC charges for alternator charging. Victron has a good one 12 or 24-volt self-sensing.

Buck converters are cheap. I go with adjustable, and yes, you can run slides. I've seen bucks at 90 amps.

I have loads in the 3000-watt range depending on climate and season. I run a 400ah battery bank at 24-volts and have a 24-volt 4kW inverter; I can run what I want.
 
Cajun? In Texas? I did not ask you. I am talking to the OP's question. Stay on thread.
 
My motorhome is all 12 volts.Is there any advantage (ignoring weight and size) to using one 200AH 24 volt battery and step it down to 12 volts or use 2 100AH batteries. Is there an efficiency loss going from 24v to 12v?

Thx
I assume you will have an inverter for ac while off grid. If your inverter is 2000W or under stay with 12 volts. If you really must have more power inverter, use 24 volts for 3000W to 4000W. You will need more battery ah.
 
Back
Top