Electrical planning

[Markusbc]

hi all,

I am in the process of planning and implementing the electrical system on my bus. Currently the bus has 2 group 31 starting batteries 12V in parallel.

Here is my dilemma, I was originally thinking of doing a 12v house system but after some research I figured that there are significant advantages to a 24V system mainly the ability to have a larger bank without going over 3 batteries in parallel. Here is where it gets interesting, i assume the ground can not be shared (the body and frame) between the two systems. Also I have a Diesel Coolant heater (proheat x45) which runs on 12Volt and is pretty power hungry at 7.5 amps.

I am planning on using Lithium iron Phosphate batteries.
What are best practices? Use a dc to dc converter and step the voltage down from 24v to 12 volts for the proheat?
Is there a way to use to separate 12v power banks (stay at 12v house system) that could be used one after the other with a automatic transfer switch when the get low?

Any thoughts are appreciated.

What have people done?

 

[dzl_]

Here is where it gets interesting, i assume the ground can not be shared (the body and frame) between the two systems.

This is actually quite alright to do. Both battery banks can be grounded to chassis. This will create a common '0 volt reference'

Also I have a Diesel Coolant heater (proheat x45) which runs on 12Volt and is pretty power hungry at 7.5 amps. I am planning on using Lithium iron Phosphate batteries.

What are best practices? Use a dc to dc converter and step the voltage down from 24v to 12 volts for the proheat?

Yes, a 24v to 12v buck converter is the usual way people solve this. Also many marine and mobile devices marketed as 12v are 12/24 volt if you look at the specs, but many (most) are not.

You can also use a 12v to 24v charger (sometimes called battery to battery charger) to charge your LFP bank safely off your vehicles charging system (This is needed with LFP even if both are 12v)

 

[Markusbc]

Thank you great info.

I am going to look into chargers, inverters, buck converters.

I was looking at the electrodacus bms, and build the system around that.

I am planning on using a 120v fridge/freezer.
From what I saw most recessed ceiling led lights run on 24volt dc. It would be easy to change the current limiting resistor to allow them to use them with 12 volts but one less thing to do, as the list is long.

How many amp hours do people have in their skoolie and what was the calculation used to come to the amp hours?

 

[dzl_]

I was looking at the electrodacus bms, and build the system around that.

There is a lot to like about that BMS, but also a lot to learn, its quite unique.


If you are looking at the SBMS0, I suggest you look at Victron's dc-dc converters. Some can be remotely switched, which makes them well matched for the SBMS


Victron products in general pair very well with the SBMS, but there are some cheaper alternatives as well.

 

[Rwnielsen]

The only definitive to that is it varies. You need to get a good idea of what you want to do. You'll have fixed loads like the refer and variable loads like lighting, TV, music etc.. Maybe it gets cold and you run a heater all night or a fan or two. For myself I would probably double my assumed needs in batteries. Are you planning on solar to supplement your power? Shore power? Generator?

 

[Markusbc]

The only definitive to that is it varies. You need to get a good idea of what you want to do. You'll have fixed loads like the refer and variable loads like lighting, TV, music etc.. Maybe it gets cold and you run a heater all night or a fan or two. For myself I would probably double my assumed needs in batteries. Are you planning on solar to supplement your power? Shore power? Generator?

yes i am planning on adding solar (around 900W), i am trying to stay away from a generator or only use it in emergencies. Shore power i will add the hook up but 99% i will be camping far away from shore power.

Doubling the amount of battery amphours is what lead me to the 24V conclusion, after reading a lot about not going over 3 cell parallel connection.

Heat is hopefully covered by the diesel heater (7amp/hour) and if i need to add a wood stove i am happy to do that.

 

[Markusbc]

There is a lot to like about that BMS, but also a lot to learn, its quite unique.


If you are looking at the SBMS0, I suggest you look at Victron's dc-dc converters. Some can be remotely switched, which makes them well matched for the SBMS


Victron products in general pair very well with the SBMS, but there are some cheaper alternatives as well.

yes i was looking at the sbms0, have you used it or are you using it?

 

[Rwnielsen]

You can get a small, 2000-2200 watt generator for 4-500 dollars that's very quiet. I bought a cheap one from Amazon that makes a racket so I use it for work. I then bought a Powermate 2200 that's very quiet. Couple that with a long, heavy duty (12 awg) extension cord and you won't even know it's running. Get a reasonably priced converter charger to supplement your solar or interface with the SBMS. Possibly as secondary array

 

[BeNimble]

I've never heard of an issue connecting 3 or more batteries in parallel. You will have to have a bus-bar setup that will handle the higher current compared to running in series with higher voltage.

If you are going with LiFePo, they are in fact 3.2v. Not sure what is available today, but I have some 180ah cells, seem to recall they had 300ah cells.

 

[Markusbc]

I have read it on a couple of solar forums, mainly because of the internal resistance of batteries, if they are not all completely identical one of them will take the brunt of the discharge. I will try and find the links.