First steps towards solar

[hclarkx]

Originally Posted by Persistent

A 48 volt system can carry four times the power in the same cable as a 12 volt system. Other equipment like inverters and chargers also can be designed to carry more power with lighter components.

I stayed with 12V. I couldn't see changing to 24V to save a 2 foot run of 1/0 cable (a second parallel one). Having half the solar controller (quantity or capacity) would be a benefit though I like having two for reliability. And I didn't like losing reliability by adding a DC-DC converter. Batteries are very reliable but I preferred two in parallel rather than two in series for an additional reliability benefit. And staying at 12V was less costly.

My son's system is 840 Ah of battery and 2 kW of solar and 3.5 kW inverter. It was built from scratch so we could have gone 24V or 48V. We priced the options and 12V was less costly. We also did a failure modes and effects analysis and found much higher reliability at 12V. And more readily available components.

We did not compare weights. That might be an advantage of higher voltage.

IIRC the efficiency (energy lost to heat) was about a wash largely because of the need for a DC-DC converter.

[hclarkx]

Originally Posted by cruizerEd

As an aside if I were going for a new system, batteries, inverter, charge controllers, and solar I'd serious look at going 24V and maybe 48V. It is way more efficient.

I'm still curious what "more efficient" means.

More efficient in power usage? (less losses?)
More efficient use of space?
More efficient use of money?

I don't mean to be contrary, but I see 24 and 48V systems described in these terms, but few specifics (as noted in my post above).

The question the OP posed is a good one and is frequently asked. But a wholesale change may not be the best recommendation.

[cruizerEd]

Originally Posted by hclarkx

Can you please explain what makes the higher voltage systems more efficient?

Start here.

A 3000 watt inverter running wide open on 12V will use at least 250A. That means you'll need 250A fuses,busses and switches. That stuff is expensive. Inverters are more efficient and possibly smaller at higher voltage. At 48V it's 62.5A. Everything can be smaller, lighter and cheaper.

12V is a standard developed over 100 years ago. We'll probably see it start slipping away.

In the 50s carse switched from 6 to 12 because they needed more power to start. Now we need a lot more power from our batteries and moving up is the best engineering decision.

[rblackburn]

Originally Posted by Persistent

I can't find the owner's manual for your inverter/charger/converter system. The brochure that you linked says it has a three stage charger that may have up to 100 amps charging capability. It does not give the charge voltage specifications nor the charge profile.

If the charger can supply at least 50 amps, it should be able to charge 200 or 300 amp hours of lithium batteries as long as the new batteries have a good battery management system.

A 300 amp hour lithium battery bank should be able to power the 2000 watt inverter. It all depends on the exact specifications for the new batteries. A 200 amp hour battery bank may limit how much an how long the inverter will supply.

Battle Born provides good customer support for what will work and what will work poorly. Feel free to contact them with you RV make and model and your inverter charger make and model. They usually say it is OK to run 200 amp hours without a B to B charger to protect the engine alternator.

Battle Born can recommend an installer who will provide an expert installation design.

From manual:

3.2.2 Battery Charger – “B3” Option: External power 120 VAC, 60 Hz is applied as explained in section 3.1.2 The internal transfer switch automatically turns the DC to AC inverter OFF and turns the three-step built-in battery charger ON. The battery charger cannot be defeated at this time and will engage even if the inverter has been set OFF manually. SPSs with the three-step battery charger feature require the transfer switch “T” option to operate.

The 3-steps of the charging process are as follows:
Bulk mode: Charging current is passed through the batteries until a factory set acceptance voltage limit is reached. The charger’s maximum output and/or the state of charge of the batteries determine the amount of current.
Acceptance mode: Charging continues with the voltage held at the accept voltage until current flow decreases to the factory set end value or the factory set acceptance mode time limit is reached.
Float mode: Battery voltage is held at a factory set value, which will neither charge nor discharge the batteries.

Condition mode occurs every 10th charge cycle between Acceptance mode and Float mode to ensure full restoration of active materials in all the plates of the battery cells.

The SPS has an automatic power sharing feature that automatically decreases the battery charger output so that the total AC input current draw by the SPS for both the AC loads and the battery charger does not exceed 30 amps AC. If the loads exceed 30 amps the charger will be at zero amp draw and the AC input circuit breaker will trip. The battery charger draw will automatically increase when the external loads are reduced if the batteries will accept more current.

[JDooley]

Battleborne does reccomend changing the BIM225 to a LI BIM225 which allows the alternator to charge for 15 minutes and rest for 15-20 minutes to allow alternator to cool, This cycle repeats over and over to prevent alternator from failing due to thermal burnout. DC to dc charger is the best way. disconnect house from BIM and you loose Boost to jump yourself. Install a cut out switch to disconnect and if needed to Boost turn switch on to jump then turn it back off. This is the setup I am installing in mine. JMHO

[rblackburn]

Originally Posted by JDooley

Battleborne does reccomend changing the BIM225 to a LI BIM225 which allows the alternator to charge for 15 minutes and rest for 15-20 minutes to allow alternator to cool, This cycle repeats over and over to prevent alternator from failing due to thermal burnout. DC to dc charger is the best way. disconnect house from BIM and you loose Boost to jump yourself. Install a cut out switch to disconnect and if needed to Boost turn switch on to jump then turn it back off. This is the setup I am installing in mine. JMHO

Cool, thanks for you input

[hclarkx]

Originally Posted by cruizerEd

Start here.

A 3000 watt inverter running wide open on 12V will use at least 250A. That means you'll need 250A fuses,busses and switches. That stuff is expensive. Inverters are more efficient and possibly smaller at higher voltage. At 48V it's 62.5A. Everything can be smaller, lighter and cheaper.

12V is a standard developed over 100 years ago. We'll probably see it start slipping away.

In the 50s carse switched from 6 to 12 because they needed more power to start. Now we need a lot more power from our batteries and moving up is the best engineering decision.

That link is pablum. Not helpful. I checked some 48V inverters. Not smaller. Not lighter. Not more efficient. Same with chargers. Fuses look identical over a wide current range. I'm back to one advantage, avoiding a bit of cable. And some disadvantages (e.g., keeping series batteries balanced).

Probably the biggest reason to stay with 12V and avoid 48V is the arc-flash problem and the problem of DC arcs being increasingly difficult to extinguish as voltage rises. Most 12V circuit breakers we use are rated 48V. They are surely okay at 48V but provide a lot of margin at 12V.

The first 12Volt automotive systems arrived in the mid-20's though most of the industry didn't switch until larger and higher compression engines came along in the 50's. But now with high-RPM starters being the norm, there's no benefit to going above 12V in cars and trucks.

[BCam]

The only real advantage I know of in higher voltage is between the solar panels and the controller. Higher voltage from the solar panels means lower amps for a given wattage. 24V = half the amperage of 12V, 48V = 1/4 the amperage, etc. This means that, for a given cable run, a smaller gauge can be used. From the controller on, assuming it's located close to the battery bank, I don't see any practical advantage in converting an RV designed to run on 12V batteries to 24V or 48V batteries.

There's no appreciable weight advantage. A 24V battery with the same capacity of two 12V batteries is going weigh about the same.

Here's a link to an article on 24V vs. 12V by Battleborn:

https://battlebornbatteries.com/12v-vs-24v/

[harryn]

I build 24 and 48 volt RV / Van power systems for people.

The benefits are really in three areas:

1) Heavy inverter users
- The same brand / size / capacity inverter is typically slightly more efficient when run at 48 volts vs 24 vs 12 volts.
- The reason is that the 120 vac sine wave peak is ~ 170 volts, so the inverter has to boost the voltage up from the DC level to the peak of that AC sine wave. The smaller the boost required, the more efficient the conversion is.

If you think about it, most 12 volt DC loads are a few hundred watts. Heavier duty inverter use is thousands of watts. That is why the efficiency benefit can make sense.

2) Regulated 12 volt output stability
- Some exhaust fans are very finicky about not exceeding ~ 13.8 volts, mostly the more feature rick versions.
- 12 volt refrigerators and 12 volt driven fuel heaters start to act up when the voltage sags too low (sometimes anything much lower than 11.8 - 12 volts.)

With 24 and 48 volt systems, the 12 volt appliances are fed by a DC - DC converter and the better ones are rock solid.

The voltage range of a 12 volt battery (especially the lead - acid types) varies easily from 11.8 - 15 volts depending the charge state and the charging voltage needed.

3) Component size
- Some components become smaller as the current drops, so the higher voltage can result in smaller components (sometimes)

Cost - is not really a benefit. In fact 48+ volt related components that have some operating margin are often more expensive, but the build quality is also quite high so they tend to be very durable, especially the domestically made items.

For most people, 24 volts is a nearly ideal setup.

48 volts is something that should be done by someone that really knows what they are doing.

Harry