Moving to 24v system, requires step down for house DC?

[phemens]

I am considering replacing my existing Samlex EVO-3012 inverter charger with a 24v unit (to repurpose the Samlex for another application.
This would work well with my battery bank, I could rewire the 6 batteries into a 3x2 24v array. I'm looking at the Victron Multiplus 3000/24, since all my other equipment is Victron and the integration would be nice.
So if I do this, I guess I would need a 12v step-down converter to supply house 12v DC? Any recommendations? Would need to supply for the usual (lights, pumop, furnace, LP detector, radio) plus landing gear, macerator pump and water transfer pump.

[phemens]

GordonThree wrote:

phemens wrote:
Just to clarify, I only run the HW heater off inverter in the afternoon if my batteries are topped up and I can leverage all my spare solar, which is usually the case. Typical overnight usage on batteries draws down to 75% or roughly 150 amp hrs consumption (running residential fridge, TV, Media player, NAS, coffee maker and LPAP), on a typical day I'm back up to 100 by 1 or 2 pm. Saves on LP when I can.

Free hot water sounds great!

Does your charge controller have a dump load / aux load output? Maybe you have it setup that way already, using a relay to switch electric on and gas off on the HWH automatically when hitting 100% SOC?

No real need to automate anything, we make very sporadic use of the HW heater, essentially just for showers, and we don't do that every day (sometimes I prefer to use a solar HW heater, the one that's in a bag, it's surprising effective - also use that for dishes mostly). The RV heater only goes on if I know we're going to take an indoors shower in the evening.

[BFL13]

time2roll wrote:

BFL13 wrote:
It is a lifestyle thing of course, but we don't have any need for hot water except in the morning. All day-before dishes saved till morning and one 6 gal tank of hot water is good for shave, showers, wash dishes.

We do all this in the evening before bed. I like to hit the ground running in the AM, not bogged down with chores from previous day. To each their own.

If you are on the road with overnight stops, yes. We generally stay in one spot for days/weeks, so no rush to put the dishes away so we can hit the road.

Going swimming up at the lake in the afternoon reduces need for showers too. Just did five weeks straight off grid at our usual campground. No issues, good solar, no limit on MW, kettle, toaster. (Having the four Wet 6s means they can take repeated 25% draws, where the previous AGMs seemed not able to for whatever reason)

12v does great at shorter 25% draws as with MW. No need for 24v in our case. Of course no off-grid air conditioning requirement which might make a diff --nice breeze off the water does that. Scenario is everything!

It seems the air conditioning requirement for many here is what is causing so much trouble folks are posting about.

[2oldman]

BFL13 wrote:
Anyway, solar to heat water late in the day seems silly to me,

Not if you shower before bed.

[time2roll]

BFL13 wrote:
It is a lifestyle thing of course, but we don't have any need for hot water except in the morning. All day-before dishes saved till morning and one 6 gal tank of hot water is good for shave, showers, wash dishes.

We do all this in the evening before bed. I like to hit the ground running in the AM, not bogged down with chores from previous day. To each their own.

[BFL13]

Can't see heating up water that is just going to get cold again overnight.

It is a lifestyle thing of course, but we don't have any need for hot water except in the morning. All day-before dishes saved till morning and one 6 gal tank of hot water is good for shave, showers, wash dishes.

As soon as the 6 gal is hot (LP), the WH is turned off. Coffee water is from a kettle or stove top. Works for us.

(DW is spring-loaded to wash anything to do with eating as soon as possible after every meal, so it took some convincing to get her to think like a guy when RVing. Perhaps it was easier to change her mind because now I am the one who has to wash all those dishes once a day, while she does the dogs. )

Anyway, solar to heat water late in the day seems silly to me, so there has to be something else to use with that extra solar in the afternoon. Run a blender to make fancy drinks?

[GordonThree]

phemens wrote:
Just to clarify, I only run the HW heater off inverter in the afternoon if my batteries are topped up and I can leverage all my spare solar, which is usually the case. Typical overnight usage on batteries draws down to 75% or roughly 150 amp hrs consumption (running residential fridge, TV, Media player, NAS, coffee maker and LPAP), on a typical day I'm back up to 100 by 1 or 2 pm. Saves on LP when I can.

Free hot water sounds great!

Does your charge controller have a dump load / aux load output? Maybe you have it setup that way already, using a relay to switch electric on and gas off on the HWH automatically when hitting 100% SOC?

[phemens]

Just to clarify, I only run the HW heater off inverter in the afternoon if my batteries are topped up and I can leverage all my spare solar, which is usually the case. Typical overnight usage on batteries draws down to 75% or roughly 150 amp hrs consumption (running residential fridge, TV, Media player, NAS, coffee maker and LPAP), on a typical day I'm back up to 100 by 1 or 2 pm. Saves on LP when I can.

[valhalla360]

3 tons wrote:

valhalla360 wrote:
So what is the goal of setting up a 24v system...if you aren't using 24v for all the DC loads?

24v systems are becoming more common on large yachts but that is because they have high wattage devices that are a long way from the battery bank and the voltage drop due to high amperage becomes a problem (Ex: Anchor winch might be 40-50ft of cable from battery to winch and a small winch might draw 250amp. By increasing the voltage to 24v, that drops to 125amp. They also may have electric sail winches, bow thrusters and other high wattage devices drawing hundreds of amps at 12v

By comparison, a slide out motor might draw 30amps and that's one of the bigger DC loads on an RV.

You’ve raised an interesting point here, one that I’ve often wondered myself?
Though I do not have long wire runs in my truck camper...I do occasionally run my 11kbtu air cond from the battery, but the biggest concern here is harmful LRA momentary voltage sag which can be reasonably addressed with a soft-start and with the rather stable voltage profile of LiFePo4...

FWIW, Victron BMV measured (at 12v) a LRA instantaneous pulse of 96a and steady running amps (after 12 min) of 88a...Using 0004, 6’ round trip cabling...

3 tons

If the goal is to run a 120v AC device off inverter, the amperage is usually addressed by placing the inverter close to the battery bank and feeding from battery to inverter with large cables...since it's only a few feet, voltage drop is usually not a big deal.

By contrast on a large cruising boat, the battery bank is typically near the stern and bow thrusters and anchor winches are at the opposite end of the boat necessitating long DC cabling runs which causes voltage drop issues.

[time2roll]

2oldman wrote:

phemens wrote:
I run a fair number of high wattage devices off the batteries, including residential fridge (lower but constant), microwave, hot water heater..

Water heater on inverter..that's unusual.

That would be a great accessory to have a heat pump water heater similar to what is available for a home. Would remove heat from the living space to have hot water. At least 2x efficiency of resistance heating the water + cooling for the living space. win-win.

[time2roll]

phemens wrote:

time2roll wrote:

phemens wrote:
So if I do this, I guess I would need a 12v step-down converter to supply house 12v DC? Any recommendations?

Victron has several to choose from. Only issue is if you will have a 12v battery buffer the converter needs to be rated for such. Any Victron should work as a direct power supply.

Thanks, not sure what you mean by 12v battery buffer? When you say any Victron should work as a direct power supply, do you mean it can manage the step down directly or as a source to a step down converter?

Victron has DC-DC converters to supply the 12v you need from a 24v source.

Battery as a 12v buffer might be for the emergency brakes but if the converter is sized properly no 12v battery should be needed.

[3_tons]

2oldman wrote:

phemens wrote:
I run a fair number of high wattage devices off the batteries, including residential fridge (lower but constant), microwave, hot water heater..

Water heater on inverter..that's unusual.

X2, while doable, resistance water heating is not very efficient without tons of solar. Typically a greater wattage draw than many air conditioners...

3 tons

[2oldman]

phemens wrote:
I run a fair number of high wattage devices off the batteries, including residential fridge (lower but constant), microwave, hot water heater..

Water heater on inverter..that's unusual.

[phemens]

I run a fair number of high wattage devices off the batteries, including residential fridge (lower but constant), microwave, hot water heater, coffee maker, occasional AC.
Last time out I blew the 500a fuse to the inverter because we ran the microwave and water heater at the same time (my error).
I already use 0000 wiring between the batteries and the inverter/charger, but it would be nice to not have my wires glow 😉

[2oldman]

3 tons wrote:
I do occasionally run my 11kbtu air cond from the battery,

Me too. Toasters and microwaves are similar in wattage draws. Wires and connectors (and batteries) can heat up quickly with those kinds of draws at 12v.

Also, my Victron 48-12 converter keeps my coach at a steady 12.8 or so volts. No high voltage during charging.