Reinvent the wheel... forklift batteries and solar.

[Brewerbob]

We have 12VDC appliances so we step-down our solar panels to 12VDC... but why? 120VAC is better for fridges, AC, even water pumps come in 12VAC. I'm reading that house panels are 36VDC. I know forklifts come in 48VDC. I don't know if they are a bunch of 12s tied in parallel-series combo for the 48VDC and current requirements. They have to be deep cycle. Granted they are $3k but still... Both 36 and 48 are multiples of 12 so even if we are using car batteries, why are we using an MPPT to step-down the voltage? I have a good handle on Ohm's Law but no experience with solar.

Is anyone using the 24VDC batteries for RV house? What are stick houses using? They don't need nor want 12VDC. What other options are out there?

Without changing the roof hatches, I have room for 13 panels up there. If I put in skylights then I wouldn't have as many. +4kW/h sounds great to me. Expensive and optimistic perhaps but nice.

[Elfie]

Hi bb.
13 panels 300 watt at $89 is not bad compared to webasto diesel heater.
Other real nice benefits is that it reduces the heat load on your roof.
Mmpt is a technology that optimizes the power from solar by modifying the load so that it is highest. The voltage and current curves of solar depend on temperature and light intensity. If one or more cells in a string that forms the panel is shaded the power curves change dramatically. An mppt controller makes the best out of it.

You can compare it a little to the torque /rpm curve of your engine. Torque x rpm =power . if your air filter clogges up ( cell shading) your engine curves change. To get the best performance out of your engine you will to run it a different rpm to get the max power.

Look up chevy volt modules on fleabay. Still a lot cheaper then lead and a lot lighter. Read up a little on max and min battery voltage and cell voltage monitoring.
A common lead acid bank benefits from cell monitoring to. That is why electric forklift batteries have a log where they write down the acid gravity and water use.

I think 4 kW solar takes you right of the grid if you adapt your lifestyle to the sun..... Use your cloth washer or hot water when the sun is shining and not at night.
An average house in the us can be self sufficient with 10 kW solar installed.
Later j

[Robin97396]

I'm not quite sure what you're getting at, but forklift batteries would be an excellent choice for house batteries if you can get a battery pack that isn't shorted out. They are quite expensive.

Ideally I'd use the battery pack from a walk behind pallet jack rather than from an electric forklift. The links between individual batteries can be changed to adjust the output of the battery pack. The good part is many of those pallet jack battery packs come with the charger when they're sold, but sadly it might be three phase. There would likely be at least one bad individual battery in the pack causing the entire pack to not charge properly, which is why they're selling the entire pallet jack.

The forklift and pallet jack batteries look pretty much like a normal battery from the top, but each battery is about 2 1/2 feet tall. Each individual battery is physically the equivalent of four to five regular batteries. They are a matched set of batteries, much the same as we match a set of house batteries. The battery packs are encased in a steel container so they can be lifted all together.

It's easily possible to find a good deal on a battery pack. I don't recommend the forklift battery packs because of their size and weight. Pallet jack battery packs are about one third the size of a forklift battery pack, and would fit neatly against a wall or even inside a custom cabinet.

Forklift battery packs are excessive in size. The pallet jack battery pack seems to be a more appropriate size for the power needs of a bus.

Personally I have reservations about putting anything that heavy into the back of a bus. If the bus crashes, that battery pack is going to keep moving.

[Brewerbob]

Originally Posted by Elfie

You can compare it a little to the torque /rpm curve of your engine. Torque x rpm =power . if your air filter clogges up ( cell shading) your engine curves change. To get the best performance out of your engine you will to run it a different rpm to get the max power.

I get that too. That all relates to Ohm's Law.

Look up chevy volt modules on fleabay. Still a lot cheaper then lead and a lot lighter. Read up a little on max and min battery voltage and cell voltage monitoring.

The battery technology I don't know. Lead acid is common and (relatively cheap). Doesn't catch on fire as often as a Samsung even when you do something stupid. Had a voltage regulator short on my first car. Sent the alternator to the battery whether it wanted it or not. When I stopped after a 2 hr drive, the acid was literally boiling in the battery.

The reading up is what I need to do.

A common lead acid bank benefits from cell monitoring to. That is why electric forklift batteries have a log where they write down the acid gravity and water use.

Already have a hydrometer.

I think 4 kW solar takes you right of the grid if you adapt your lifestyle to the sun..... Use your cloth washer or hot water when the sun is shining and not at night.
An average house in the us can be self sufficient with 10 kW solar installed.
Later j

4kW a day might be enough without using heavy AC. 4 KWh should be more than enough.

[Brewerbob]

Originally Posted by Robin97396

I'm not quite sure what you're getting at, but forklift batteries would be an excellent choice for house batteries if you can get a battery pack that isn't shorted out. They are quite expensive.

Well, what I'm really wondering is the 12V step-down from the 18V solar cell. I truly want 120VAC not 12VDC so why step it down at all? I get that the controller is conditioning the voltage so the batteries can be charged (load, shading, isolating, etc). But if a house panel puts out 36VDC +/- XX then use a battery higher than 12 VDC.

[Robin97396]

That's where the lead acid pallet jack batteries would shine. Most of those are either 24 or 36 volt already, but you can reconfigure the way the individual batteries are connected to get 36 volt to match your solar panels.

The problem with forklift batteries is their rather extreme cumulative weight within the batter pack. These could work if you were able to get a good battery pack. Another issue is when there's a problem with the batteries, they aren't serviced by normal battery shop. You'd have to go to a shop that services electric forklifts.

I'm no battery expert, but given a choice I'd go for the Volt battery pack.

[jazty]

For the DC side most people use 12vdc because there are many affordable appliances built for vehicles, RVs and boats. 24vdc and 48vdc appliances are also out there, but typically demand a higher price point. 48vdc is more common in commercial boats and expensive yachts as well as in the telecom industry.

A consideration for keeping DC voltage low is safety. When you start working with switches and high voltage DC you enter into an expensive, or dangerous world. Expensive if you do it right with high-voltage DC equipment, or dangerous if you use inappropriate gear.

The big problem is that DC likes to arc between contacts. As voltage increases so does the distance in which an arc can be sustained. Arcing within switches or breakers creates heat and fire.

[Brewerbob]

Originally Posted by jazty

A consideration for keeping DC voltage low is safety. When you start working with switches and high voltage DC you enter into an expensive, or dangerous world. Expensive if you do it right with high-voltage DC equipment, or dangerous if you use inappropriate gear.

I don't know that I would call 48VDC high voltage. I get nervous about 240.

The big problem is that DC likes to arc between contacts. As voltages increase so does the distance in which an arc can be sustained. Arcing within switches or breakers creates heat and fire.

15,000 volts per inch of air. I don't know at what humidity that is tho.

[jazty]

Originally Posted by Brewerbob

I don't know that I would call 48VDC high voltage. I get nervous about 240.

In the DC world above 48vdc is getting into the higher voltage side of non-industrial use.

Originally Posted by Brewerbob

15,000 volts per inch of air. I don't know at what humidity that is tho.

15000 volts DC ? Under load you can get an arc fairly easy with DC. I haven't had an inch, but 1/2"? Sure.. And I wasn't anywhere near 7500vdc. I have a 30vdc MIG welder and I can sustain about a 1/4" arc.

Or are you talking about 15000 volts AC?

Here, check out his lil' video. He gets about an inch worth of arcing, I reckon:

https://www.youtube.com/watch?v=Zez2r1RPpWY

[Brewerbob]

Originally Posted by jazty

In the DC world above 48vdc is getting into the higher voltage side of non-industrial use.

Yeah, figured as much.

Or are you talking about 15000 volts AC?

Had to be AC since they were using just a transformer for a Jacob's ladder.

It was in the HS Electronics textbook at 15K for one inch of air. Grab a doorknob in the winter and you're looking at better than 2k. No real current but still enough to fry the hell out of electronics.

Originally Posted by wiki

A Jacob's ladder (more formally, a high voltage traveling arc) is a device for producing a continuous train of large sparks that rise upwards. The spark gap is formed by two wires, approximately vertical but gradually diverging from each other towards the top in a narrow V shape. It was named for the "ladder to heaven" described in the Bible.

When high voltage is applied to the gap, a spark forms across the bottom of the wires where they are nearest each other, rapidly changing to an electric arc. Air breaks down at about 30 kV/cm,[2] depending on humidity, temperature, etc. Apart from the anode and cathode voltage drops, the arc behaves almost as a short circuit, drawing as much current as the electrical power supply can deliver, and the heavy load dramatically reduces the voltage across the gap.

...

This cycle leads to an exotic-looking display of electric white, yellow, blue or purple arcs, which is often seen in films about mad scientists. The device was a staple in schools and science fairs of the 1950s and 1960s, typically constructed out of a Model T spark coil or any other source of high voltage in the 10,000–30,000-volt range, such as a neon sign transformer (5–15 kV) or a television picture tube circuit (flyback transformer) (10–28 kV), and two coat hangers or rods built into a V shape.

[family wagon]

Dielectric strength of air seems high at 3 megavolts per meter (76 kV per inch) (as per wikipedia) however that's the voltage needed to spontaneously arc across a gap. The wikipedia article also notes that "Because dielectric materials usually contain minute defects, the practical dielectric strength will be a fraction of the intrinsic dielectric strength of an ideal, defect-free, material."

The subtle point made by jazty is important: when a current is mechanically switched, there's an arc. There's always an arc; we just forget it's there because it is contained inside the case of the switch and we don't see it. If the switch isn't up to the task for the current and voltage being managed, the arc may endure longer than it's supposed to (even indefinitely). That's the principle behind dc arc welding -- strike the electrodes together, whether buzz box, MIG, TIG, whatever -- then pull back and maintain the arc. So long as the source can keep enough current flowing to keep the air hot and ionized the arc will survive even with just a few tens of volts. Anyway, that's part of why seemingly low voltage dc can still present a fire hazard, and it's why the variety of published dielectric strengths for air don't really matter to low voltage equipment.

As for converting higher open circuit voltage solar panels down for 12 volt batteries versus other voltages: I suspect step-down aka buck converters can be designed to achieve similar efficiency levels regardless of the input-to-output voltage ratio. Historical inertia more than anything else is probably what keeps us coming back to dc designs at 12 volts.

[Brewerbob]

Originally Posted by family wagon

Dielectric strength of air seems high at 3 megavolts per meter (76 kV per inch) (as per wikipedia) however that's the voltage needed to spontaneously arc across a gap. The wikipedia article also notes that "Because dielectric materials usually contain minute defects, the practical dielectric strength will be a fraction of the intrinsic dielectric strength of an ideal, defect-free, material."

The subtle point made by jazty is important: when a current is mechanically switched, there's an arc. There's always an arc; we just forget it's there because it is contained inside the case of the switch and we don't see it. If the switch isn't up to the task for the current and voltage being managed, the arc may endure longer than it's supposed to (even indefinitely). That's the principle behind dc arc welding -- strike the electrodes together, whether buzz box, MIG, TIG, whatever -- then pull back and maintain the arc. So long as the source can keep enough current flowing to keep the air hot and ionized the arc will survive even with just a few tens of volts. Anyway, that's part of why seemingly low voltage dc can still present a fire hazard, and it's why the variety of published dielectric strengths for air don't really matter to low voltage equipment.

Yeah, I get that arcs and sparks are bad when they are in your electrical panel.

Forklifts do catch fire but not every day so there are switches, controllers and whatever else needed to operate them safety.

As for converting higher open circuit voltage solar panels down for 12 volt batteries versus other voltages: I suspect step-down aka buck converters can be designed to achieve similar efficiency levels regardless of the input-to-output voltage ratio. Historical inertia more than anything else is probably what keeps us coming back to dc designs at 12 volts.

That part is the unacceptable part. I can accept that it'll cost a $1000 instead of $10 to do the same thing but "we haven't gotten around to it yet" doesn't sit well.

[djthe3rd]

Lithium

https://www.youtube.com/watch?v=J-kND4PaZm8

These guys explain in detail why lithium is the better choice very well.

However they use very expensive lithium batteries. I can buy the same battery they have for 5k for ~1300 and run a 48v system which is very efficient for solar and inverting.

Tesla batteries, each 18650 battery that make up a pack of 444 18650's are fused by a burn away wire on the positive and negative terminal on all 444 cells per 24v pack they use in their cars. If anything goes wrong with one of the cells, a short for example, it disconnects itself and the rest of the pack keeps doing its job. It's an ingenious design and nothing battery wise as far as output/charging/cycling/weight can hold a candle to.


Tesla Model S battery life: what the data show so far

Tesla Model S battery module, 24V, 250Ah, 5.3kWh, 444 Panasonic 18650 3400mAh | eBay

Nickel iron forklift batteries are pretty cool though, edison thought they would never be beaten. Now we have hydrogen fuel cells on the space station that make power for everyone up there and its exhaust makes water for the crew to drink.

[superdave]

Originally Posted by Brewerbob

Well, what I'm really wondering is the 12V step-down from the 18V solar cell. I truly want 120VAC not 12VDC so why step it down at all? I get that the controller is conditioning the voltage so the batteries can be charged (load, shading, isolating, etc). But if a house panel puts out 36VDC +/- XX then use a battery higher than 12 VDC.

don't look at it like your loosing that power, if you have a 24 volt panel putting out 10 amps the charge controller will put out 20 amps into your atteries at 12 volt. if you have a 24 volt system you need a panel voltage of at least 36 volt. it needs to make up for clouds shading dust everything. I have a 24 volt system at my house, the voltage raises to 30.9 volts for 2 hours then floats the rest of the day at 26.4 .

[Mark_In_MA]

Originally Posted by Brewerbob

We have 12VDC appliances so we step-down our solar panels to 12VDC... but why? 120VAC is better for fridges, AC, even water pumps come in 12VAC. I'm reading that house panels are 36VDC. I know forklifts come in 48VDC. I don't know if they are a bunch of 12s tied in parallel-series combo for the 48VDC and current requirements. They have to be deep cycle. Granted they are $3k but still... Both 36 and 48 are multiples of 12 so even if we are using car batteries, why are we using an MPPT to step-down the voltage? I have a good handle on Ohm's Law but no experience with solar.

Is anyone using the 24VDC batteries for RV house? What are stick houses using? They don't need nor want 12VDC. What other options are out there?

Without changing the roof hatches, I have room for 13 panels up there. If I put in skylights then I wouldn't have as many. +4kW/h sounds great to me. Expensive and optimistic perhaps but nice.

It's about efficiency - but not the efficiency of the solar panels, or the chargers.

It's about the efficiency of the green pieces of paper in our wallets - Its often cheaper to deal with 12-volt systems because, at least at the moment, they tend to be the most prevalent, and therefore cheapest. Most people are also set up so that a single 12-volt battery is the smallest "individual" component in their system - so if one goes bad, they just replace it. It's not like an electric car has a larger battery - it just has tons and tons of smaller ones grouped together into cells, that make up the whole "battery."

There's also something nice about being able to replace a failed component at almost any automotive store in the country - 12v deep cycle batteries aren't that hard to find.

[superdave]

Originally Posted by Mark_In_MA

It's about efficiency - but not the efficiency of the solar panels, or the chargers.

It's about the efficiency of the green pieces of paper in our wallets - Its often cheaper to deal with 12-volt systems because, at least at the moment, they tend to be the most prevalent, and therefore cheapest. Most people are also set up so that a single 12-volt battery is the smallest "individual" component in their system - so if one goes bad, they just replace it. It's not like an electric car has a larger battery - it just has tons and tons of smaller ones grouped together into cells, that make up the whole "battery."
false
There's also something nice about being able to replace a failed component at almost any automotive store in the country - 12v deep cycle batteries aren't that hard to find.

yes 12 volt systems are most popular in a vehicle.
if a attery fails you need to replace all of them at once , you never miss match.12 volt atteries are not true deep cycle atteries,dont waist your money.

[miltruckman]

My house/solar battery bank is set up for 24vdc. I am using eight 12v golf cart batteries in a series parallel configuration. Things I run on 24vdc: all led lighting, diesel fired furnace, diesel fired water heater, water supply pump, pumps under kitchen and Bathroom sinks that pump to the waste tank. Fans by the driver & passenger seating and in the back bunks. And The Magnum split phase inverter.

Unless you are running a large inverter system and all AC appliances I would not use a 48vdc battery bank. As there are very few items available to run on 48vdc.

Bill

[jazty]

Originally Posted by superdave

12 volt batteries are not true deep cycle batteries, don't waist your money.

This is false. There are many true deep cycle 12v batteries. Maybe you're thinking about marine batteries? Those are half way between a starting battery and a deep cycle.

12v US 185HC XC2 - U.S. Battery | Leader in Deep Cycle Batteries
12v T-1275 | Trojan Battery Company

That being said, the price point for the common 6v deep cycle batteries is probably better. I had a predefined battery bay to fill and wanted to get as much battery in there as possible. 3x 12v deep cycle batteries (for a total of 455Ah) fit perfect. There wasn't enough room to fit 4x 6v batteries and 2x 6v batteries would have provided much less power.

[Kubla]

Golf cart batteries are the best bang for the buck, Edison batteries would be great but require a different charger and cost a lot

[Brewerbob]

Originally Posted by miltruckman

My house/solar battery bank is set up for 24vdc. I am using eight 12v golf cart batteries in a series parallel configuration. Things I run on 24vdc: all led lighting, diesel fired furnace, diesel fired water heater, water supply pump, pumps under kitchen and Bathroom sinks that pump to the waste tank. Fans by the driver & passenger seating and in the back bunks. And The Magnum split phase inverter.

Unless you are running a large inverter system and all AC appliances I would not use a 48vdc battery bank. As there are very few items available to run on 48vdc.

Bill

I am looking for diesel heat (water, furnace, stove). I would like enough solar to run air conditioning. The gf wants a dryer. I just don't see that one happening. Anyone make one of those in diesel?