I'm a noob setting up a 24v system. Help me not blow something up

[Slowman]

I'm building a semi-budget expedition truck and the base vehicle is a 2002 Superduty 4x4 7.3 diesel w/ a 270A single alternator. I have absolutely no need for shore power. The elec system will be around 800w of solar charging a pair of 300Ah LiFePo4 batteries joined in series to make a 24w system. My appliances will all run on 24v power (fridge, freezer, water pump) or on 110v and I'll put in a 4000w 24v inverter. I've done an energy audit and I'll use about 3000Wh per day of power. I drive quite a bit when I'm out in this rig. At least every second day. My current question (pardon the pun) is how to charge the batteries with the alternator. I don't have the "ambulance package" but I can add a second alternator without too much trouble. Or, I can do it via a DCDC charger that will convert from 12v to 24v. For sure, what I can do is fudge it up royally. Hence my asking you all and this is my first post here so I hope this conforms to the culture of the community.

 

[Dave in AZ]

That alternator can support a lot of amps. Victron 12/24 Orion smart chargers. Probably 15A, 360W, but you can put multiple in parallel.

 

[Aussieguy]

so if your truck is 12v why not use 12v appliances

800w of solar is not in the realm of needing to go to the expense of 24v

you can use 10g to a 50amp controller
wire half the panels in series for higher voltage then join the 2 strings in parallel
40v @20amps?
my system 50amp mppt 740w panels (3 x 370w) + 200ah battery cost under $1000

what appliance you intend to run will use 3000wh

my 12v circuits mainly 10foot fridge and furnace usage... uses about 30% of my 200ah battery over night
740w of solar recharges that by 2 pm

I use phones/ipads for TV USB battery powered 7"fans


If I want air conditioning can mooch dock or pay for a campsite with power

where the heck do you put 800w of panels on the roof?

 

[Rednecktek]

you can use 10g to a 50amp controller

Wait, whut?

OP: You've got a lot of headroom on that alternator, get a DC-DC that will upconvert to 24v and you'll be good.

4kw of inverter is pretty hefty, what are your big loads?

 

[Aussieguy]

Wait, whut?

I got 2 solar panels , 370w (37vx 10amp) and used the manufacturer's installed 10g solar wires to the controller
the sticker says max 30amps (assuming for a PWM of around 20v)


put the 50 amp controller next to battery and then used 4g to the battery... controller could not fit bigger wire to terminals)


is there something wrong with my theory on using this factor wiring ?
using 50amp mppt and panels producing 37v and max of 10amps each .......... 2 x panels in parallel

I checked with wiring charts and they said @ 37v @20amps............ 10g would work
hasn't melted any wires in the Florida sun ........... so far

 

[HarryN]

I am just posting this to help clarify my mind on your project:

Battery pack ~ ( 300 amp-hrs ) x ( 24 volt ) ~ 7 kW-hrs of battery storage.

Solar ~ 800 watts, so in a typical day ( 800 watts ) x ( 50% ) x ( 6 hrs / day ) ~ 2400 watt-hrs / day generated solar generated ( not in the winter, but other wise )

Estimated power use ~ 3000 watt-hrs / day

Diesel engine, so reduced power demand to run engine so driving around can probably tap into 100 - 120 amps from the alternator at highway speed, 50 amps at stop and go.

Alternator charging ~ ( 50 amps ) x ( 12 volt ) x ( 2 hours average driving / day ) ~ 1200 watt-hrs / day from alternator main alternator

____________

Seems in general viable.

It "might" make sense to consider to have dual starter batteries to deal with the highly variable nature of power output from alternators while driving around. Maybe with the diesel, you already have them.

There are 24 volt alternators on the market that can be set up to charge your Li battery pack directly, they do need an external controller to deal with a pack that size or they can burn out. There are some real details to follow to make that all work but it can.

 

[Rednecktek]

Sorry, the wording implied you were pumping 50a through a 10awg wire. Whew!

 

[RV8R]

I am just posting this to help clarify my mind on your project:

Battery pack ~ ( 300 amp-hrs ) x ( 24 volt ) ~ 7 kW-hrs of battery storage.

Solar ~ 800 watts, so in a typical day ( 800 watts ) x ( 50% ) x ( 6 hrs / day ) ~ 2400 watt-hrs / day generated solar generated ( not in the winter, but other wise )

Estimated power use ~ 3000 watt-hrs / day

Diesel engine, so reduced power demand to run engine so driving around can probably tap into 100 - 120 amps from the alternator at highway speed, 50 amps at stop and go.

Alternator charging ~ ( 50 amps ) x ( 12 volt ) x ( 2 hours average driving / day ) ~ 1200 watt-hrs / day from alternator main alternator

____________

Seems in general viable.

It "might" make sense to consider to have dual starter batteries to deal with the highly variable nature of power output from alternators while driving around. Maybe with the diesel, you already have them.

There are 24 volt alternators on the market that can be set up to charge your Li battery pack directly, they do need an external controller to deal with a pack that size or they can burn out. There are some real details to follow to make that all work but it can.

I like the 24v added alternator / controller idea to charge the 24vdc 300Ah LFP battery bank.

@Slowman assuming your energy audit is correct, your 7kWh storage @ 3kWh per day will give you about 2 days use without charging. Solar & Sun will assist, but worse case scenario after the 7kWh is depleted, how long would it take to recharge your battery bank using a 24v dedicated alternator @HarryN has suggested ?

To answer that, you need to find out the recommended charge power your batteries can be set up to take (without knowing your chosen battery I am guessing 2.4kW rate) & what the alternator / controller @HarryN is suggesting can give.

VDC is a much different animal than VAC ,,, Thus things like “circuit length” matters. To get around a long circuit length a DIY can consider DC - AC - DC but that brings in complexity & inefficiency.