48v - 12v hybrid systems - alternator charging

shirk

Active member
Currently researching for a future build an looking at electrical options. My end goal is to go full electric for everything in the camper, the camper will be a hard sided pop-up on a full size domestic truck and capable of primary winter use. The major power draw will be a small heat pump system for heating. The winter use will be weekends so need to heat for 2 full nights.

Most people their biggest power draw is trying to run an air conditioner. In looking into how much power is needed and how to keep it charged I've come across the idea of a hybrid 48v - 12v system.

Safiery in Australia has posted info on this on their site.


The key to the system is a 3000kw bi-directional DC-DC converter.

For my main usage solar is nearly useless as a charging source so the ability to re-charge in short time via alternator is attractive.

Anyone else looking at 48v systems?
 

Chuck1

Active member
48v alternator n battery's then use a 48-12v buck for the 12v loads.

Bank size depends on to many factors to estimate, if you build it cells are nearing $150 kwh , $1000 in cells can build a big battery.
 

BobInTheAspens

New member
I used a 24-12v system on a boat for years - worked well. 48-12v would certainly be doable.

As far as the battery bank goes, there is no advantage. Your 48v bank will be the same size as a 12v bank, just different wiring.

Charging is the big advantage. As you know, alternators of over about 200 amps are expensive and large. Basically, charging at 48v means an alternator of a given size can charge your battery 4x as fast. And, you can use a cheap alternator, and just juice up the output voltage. An ordinary alternator, say 80 amps, can happily produce 80 amps at any voltage you want, including 48v. Belts will have to handle the load, and an external regulator will be needed. If you want, you can do what I did on my boat, and buy a $20 old-fashioned mechanical voltage regulator. Then just bend the spring holder until you get 48v output.

The big draws on your system will be the inverter, and your heat pump. A 48v inverter can be much smaller and lighter than a 12v one, and perhaps cheaper. Would your heat pump run on 48v DC? Using the inverter to up the voltage to 110v for the heat pump means another big loss in efficiency.

But, consider alternatives. For winter use, a $500 propane heater, as sold for boats, would work great. Google "West Marine propane cabin heater". It would be safe, simple, efficient, and relatively cheap to buy and operate. The huge advantage of propane is energy density. A pound of propane has 500 times the amount of heat in it compared to a pound of battery. That's huge. That means you can just size your battery system to run lights, maybe a fridge, etc. A simple dual battery system, with only a fairly small 2nd battery would work fine.

I think that having a propane tank that would run your rig for weeks or months would be a big advantage over a battery bank that would be dead after a couple of days.
 

shirk

Active member
I used a 24-12v system on a boat for years - worked well. 48-12v would certainly be doable.

As far as the battery bank goes, there is no advantage. Your 48v bank will be the same size as a 12v bank, just different wiring.

Charging is the big advantage. As you know, alternators of over about 200 amps are expensive and large. Basically, charging at 48v means an alternator of a given size can charge your battery 4x as fast. And, you can use a cheap alternator, and just juice up the output voltage. An ordinary alternator, say 80 amps, can happily produce 80 amps at any voltage you want, including 48v. Belts will have to handle the load, and an external regulator will be needed. If you want, you can do what I did on my boat, and buy a $20 old-fashioned mechanical voltage regulator. Then just bend the spring holder until you get 48v output.

The big draws on your system will be the inverter, and your heat pump. A 48v inverter can be much smaller and lighter than a 12v one, and perhaps cheaper. Would your heat pump run on 48v DC? Using the inverter to up the voltage to 110v for the heat pump means another big loss in efficiency.

But, consider alternatives. For winter use, a $500 propane heater, as sold for boats, would work great. Google "West Marine propane cabin heater". It would be safe, simple, efficient, and relatively cheap to buy and operate. The huge advantage of propane is energy density. A pound of propane has 500 times the amount of heat in it compared to a pound of battery. That's huge. That means you can just size your battery system to run lights, maybe a fridge, etc. A simple dual battery system, with only a fairly small 2nd battery would work fine.

I think that having a propane tank that would run your rig for weeks or months would be a big advantage over a battery bank that would be dead after a couple of days.
Yes the charging is the main advantage sought with the hybrid system.

Our biggest power draw would be a 48V DC heat pump, and induction cooktop. Smaller draw would be a HRV (heat recovery vent) for the fresh air circulation rather than just the usual pair of roof vent fans.

The goal is full electric no gas system. While a heater like the propane Propex can be used while driving it's not something I feel comfortable with, same with leaving it unattended to hold a lower set temp all day while skiing.

We would completely skip solar.

Some more reading an researching and I have found an interesting project on the marine side. A company called Integrel is doing a hybrid voltage system pulling 48v off a unique alternator/generator. They are able to generate a max of 9kw off 100kw marine diesel engines. Claiming 3.5kw at idle.


Their "alternator on steroids" is one of the keys.

How is the Integrel system different from a high power alternator?
The Integrel system is much more than just a generator; it is a complete power generation, storage, conversion and distribution system.
Focussing on the Integrel generator itself, this is manufactured specifically for Triskel Marine and is very different from a conventional high-power alternator:
  • The generator will deliver its rated power continuously. For example, with an ambient temperature of 25C the generator will deliver a constant 8.3kW.
  • The coupling of the magnetic flux between the rotor and stator has been dramatically improved to give very high generation efficiency.
  • The windings have been changed to give the specific voltage range we need and to provide unusually high power output at low revs. With a suitable engine, up to 3.5 kW of output DC power is available at engine idle.
  • The generator itself has no embedded electronics and much improved cooling air flow to cope with the higher power output.
  • The customised engine mountings are specifically designed to minimise side loads on the engine, to eliminate shock loading and to maximise belt life.
  • The control system is radically different from that of a conventional alternator (see next question).
Their other key is they are exploiting a gap between engine efficiency and prop efficiency, not relevant to vehicles but interesting.

Would be really really nice to be able to dump 3.5 kw into a lithium bank at idle.
 

shirk

Active member
Looks like Wakespeed Offshore is also coming out with a bidirectional buck-booster converter to allow these hybrid systems.


More info in their pdf.
http://wakespeed.com/2020PricingGuide.pdf

Calex also with a 3kw unit.
 

Rando

Explorer
Currently researching for a future build an looking at electrical options. My end goal is to go full electric for everything in the camper, the camper will be a hard sided pop-up on a full size domestic truck and capable of primary winter use. The major power draw will be a small heat pump system for heating. The winter use will be weekends so need to heat for 2 full nights.

Most people their biggest power draw is trying to run an air conditioner. In looking into how much power is needed and how to keep it charged I've come across the idea of a hybrid 48v - 12v system.

Safiery in Australia has posted info on this on their site.


The key to the system is a 3000kw bi-directional DC-DC converter.

For my main usage solar is nearly useless as a charging source so the ability to re-charge in short time via alternator is attractive.

Anyone else looking at 48v systems?

Have you done a ballpark calculation of what your energy needs will be? A small number of folks have successfully run AC off batteries for well insulated campers, but they typically need a large solar array to keep up. In most cases, heating takes more power than cooling - simply because the delta T is greater. Cooling from 95F to 75F is only 20F delta, whereas even heating from only 25F to 65F is already twice the delta and twice the energy.

On occasion we have used an electric space heater to keep our FWC (admittedly not very well insulated, but also not very large) warm while winter camping with plugins. It was about 750W to keep it warm at 25 - 30F out, that would 36KWh for 2 day stay, or a LOT of batteries.

Anyway before you get into the details of the battery bank configuration, figure out if the energy budget is even close to doable. I suspect it is going to be a stretch.
 

shirk

Active member
A heat pump is MUC MUCH more efficient than an electrical element heater.

Also modern AC and heat pump units that are designed to run natively off DC are again much more efficient.

Your 750w is about the right amount of heat...just the wrong way to product it.

750w = approx 2500 btu.

Efficient DC based heat pump will use about 240w to product 4000 btu.


Looking at residential unit that is native DC and larger yields even lower power draw when you run them on their lowest setting.


3800 btu (1100w) is produced from 90w. Even if it's off by 50% and we say we need 135w. If it runs 14hrs straight it would consume 1890w for a night. A single 50ah 48v covers this.

With an ability to drop 3kw back into that battery you can top that back up in 40 minutes run time, split that into 20 minutes in the morning before going skiing and 20 minutes after you get home and it's not ever a noticeable amount of time to your day.

This doesn't account for a couple meals of cooking on an induction cooktop (pre-made meals from home to cut down on cook time) or lights and other uses but those are pretty small in comparison. The rough proof of concept calculations are working out. I think we'll see more and more units go all electric as time goes on and the 48v will help it along. If you read up on the mild hybrid vehicles coming they'll be on a 48v system so the power generation is going to be built right in (See RAM/Jeep etorque)
 

Rando

Explorer
A heat pump coefficient of performance is strongly dependent on the temperature differential. Assuming an outside temperature around 25F, the COP for a good air source heat pump is around 3, meaning you could only need 250W to produce 750W of heat - that is still 12kWh of battery for 48 hours. It gets worse as the temperature decreases as you need more heat and the COP decreases - if the outdoor temperature is 0F the COP is often less than 2.

It would be thermodynamically impossible to get 1100W from 90W (COP of 12) with at a source temperature below 40F due to the Carnot cycle limits. It would be worth looking up the specific COP for the heat pumps you are considering as a function of temperature differential (aka 'lift'), without knowing the source temperature and differential, their output and energy use is kind of meaningless.
 
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