Solar Power for The Derelicte Bus

[Velocipedic]

Originally Posted by Mr4btTahoe

You could always run 12v off the starting batteries with a low voltage shut off of some sort...


Massive inverters at 12v require LOTS of amperage. At its rated power, that inverter would be pulling almost 340 amps from the battery bank... at full surge capacity... 750 amps.


Running the same power levels at 24v cuts that in half... at 48v, you are down to ~84 amps for the same wattage. That means smaller wiring... that means a much more manageable battery bank... cheaper charge controllers.. etc.


If you want to stay at 12v... then step down the inverter size a good bit.


The most I would run would be 2kw and thats pushing it for most. 1500w would be better. If you need 4kw+ on a regular basis, get a generator or find ways to decrease your power demands.

Sorry, the inverter is 3000, not 4000. That means 250 amps at max rated (excluding surge) so the main issue will be cable heat... I think. I did read that large inverters require a lot of amperage at idle, but even still, with my solar input, I'm not super concerned about running out of amps... I'm worried about killing the batteries.

I will need 3000 on a semi-regular basis and for longer than just a 20 second surge as specified by the manufacturer (air conditioner and a few appliances). I'd really like to go without a generator as much as possible... to the point of not even having one.

[Rivetboy]

" I will need 3000 on a semi-regular basis and for longer than just a 20 second surge as specified by the manufacturer"

Many might find this portion of the system design needs a bit more engineering

[Velocipedic]

Originally Posted by Rivetboy

" I will need 3000 on a semi-regular basis and for longer than just a 20 second surge as specified by the manufacturer"

Many might find this portion of the system design needs a bit more engineering

How so? As far as I know it isn't a constant 250 amp draw, but only drawing amps as needed. It would be 5-6 minutes of 3000W usage a few times a day.

The 3000W inverter seems like the best option for this.

[PNW_Steve]

Originally Posted by Rivetboy

" I will need 3000 on a semi-regular basis and for longer than just a 20 second surge as specified by the manufacturer"

Many might find this portion of the system design needs a bit more engineering

I agree.

Notable quote from someone way smarter than me: "you need to think outside of the 12 volt box"

https://en.m.wikipedia.org/wiki/Peukert%27s_law

[Iceni John]

The generally-accepted wisdom on the NAWS forum is that a 2000W inverter is the biggest that should run off 12V, and anything bigger than that will cause too much voltage drop from the batteries unless you have a HUGE battery bank (and an equivalently huge PV array to charge them, and suitable charge controllers). The folk there know all there is to know about solar and renewable sources, and I'm happy to follow their advice. That is why I have a Magnum MS2000 inverter for my 12V system that will eventually have about 900aH of golfcart batteries, and to effectively charge that amount of batteries I have 2kW of solar running through two Morningstar TS-MPPT-60 charge controllers. Everything has to be balanced. Even the cables and connectors have to be suitable for the current involved: I use 4AWG into each CC, 2AWG from each CC to the batteries, 4/0 from the house batteries to the starter (for emergencies), 2/0 from each bank of house batteries to their 250A Schottky diodes, and 4/0 from the combined DC battery output to the Magnum inverter, along with a 250A fuse. I want negligible voltage loss under load, and no heat buildup in the cables or connections at any time. We're dealing with potentially-lethal currents here that could burn everything to a crisp, so I'm not taking any chances.

John

[PNW_Steve]

Originally Posted by Iceni John

The generally-accepted wisdom on the NAWS forum is that a 2000W inverter is the biggest that should run off 12V, and anything bigger than that will cause too much voltage drop from the batteries unless you have a HUGE battery bank (and an equivalently huge PV array to charge them, and suitable charge controllers). The folk there know all there is to know about solar and renewable sources, and I'm happy to follow their advice. That is why I have a Magnum MS2000 inverter for my 12V system that will eventually have about 900aH of golfcart batteries, and to effectively charge that amount of batteries I have 2kW of solar running through two Morningstar TS-MPPT-60 charge controllers. Everything has to be balanced. Even the cables and connectors have to be suitable for the current involved: I use 4AWG into each CC, 2AWG from each CC to the batteries, 4/0 from the house batteries to the starter (for emergencies), 2/0 from each bank of house batteries to their 250A Schottky diodes, and 4/0 from the combined DC battery output to the Magnum inverter, along with a 250A fuse. I want negligible voltage loss under load, and no heat buildup in the cables or connections at any time. We're dealing with potentially-lethal currents here that could burn everything to a crisp, so I'm not taking any chances.

John

NAWS is a great resource.

Another good one is www.solarpaneltalk.com

Edit: Another inverter/battery discussion - https://www.solarpaneltalk.com/forum...-size-tutorial

[Rivetboy]

Originally Posted by Velocipedic

How so? As far as I know it isn't a constant 250 amp draw, but only drawing amps as needed. It would be 5-6 minutes of 3000W usage a few times a day.

The 3000W inverter seems like the best option for this.

That kind of equates to taking it up to a little past redline a few times a day but it is ok because it is down hill.

[Velocipedic]

Originally Posted by Iceni John

The generally-accepted wisdom on the NAWS forum is that a 2000W inverter is the biggest that should run off 12V, and anything bigger than that will cause too much voltage drop from the batteries unless you have a HUGE battery bank (and an equivalently huge PV array to charge them, and suitable charge controllers). The folk there know all there is to know about solar and renewable sources, and I'm happy to follow their advice. That is why I have a Magnum MS2000 inverter for my 12V system that will eventually have about 900aH of golfcart batteries, and to effectively charge that amount of batteries I have 2kW of solar running through two Morningstar TS-MPPT-60 charge controllers. Everything has to be balanced. Even the cables and connectors have to be suitable for the current involved: I use 4AWG into each CC, 2AWG from each CC to the batteries, 4/0 from the house batteries to the starter (for emergencies), 2/0 from each bank of house batteries to their 250A Schottky diodes, and 4/0 from the combined DC battery output to the Magnum inverter, along with a 250A fuse. I want negligible voltage loss under load, and no heat buildup in the cables or connections at any time. We're dealing with potentially-lethal currents here that could burn everything to a crisp, so I'm not taking any chances.

John

What is a HUGE battery bank then? I'm going to get six of these batteries which will put me at 1575ah, wired for 12V. I have 1.6kW of solar. I'm purchasing two charge controllers as you've listed above and similar cabling.

[Velocipedic]

Originally Posted by Rivetboy

That kind of equates to taking it up to a little past redline a few times a day but it is ok because it is down hill.

I'd hate doing that on a regular basis... mostly because redlining electrical equipment seems worse than having thicker cables and other redundancies.

[Iceni John]

1.6 kW of PV is not enough to adequately charge 1575 aH of batteries on a vehicle all year round. (Why do you need so much battery capacity? I hope you're not planning to heat water or the interior that way! One or two minisplit A/Cs won't need that much either.) That is about a 6% charge rate, barely above the minimum recommended. The NAWS gurus strongly recommend charging FLA batteries at between 5 and 13% of their 20-hour rate, and I would suggest aiming for the upper end of that range if it's on a bus where insolation and orientation isn't always ideal. You also have to think how well you can charge on a dull winter day when the sun is low and sets early. If you cannot charge your batteries to 100% every day they will end up being deficit-charged, and that will lead to their early demise. Imagine if you charge them to 98% each day: after just one week they are at about only 85% of their full charge, and a slow death is inevitable. This is why I have sufficient PV to charge at about 13%, so even in winter I can keep my banks fully charged.

Six of those batteries weigh about 750 pounds. That's a lot! That much weight needs some careful thought about W&B and location. Because they're not AGMs they will need regular watering and SG checks, so they will need to be on pull-out trays to do so. Making trays to handle that much weight will be an engineering challenge in itself, plus sufficient space must be maintained above them for ventilation and out-gassing when being charged. Why not just use good ol' golfcart batteries that are still the best bang for the buck in terms of dollars per watt, and they're readily available everywhere in case you need to replace any wherever you are.

As others here have mentioned, you need to think through your planned system carefully. As it stands now, it will work, sort of, but not well and not for long.

John

[Velocipedic]

Originally Posted by Iceni John

1.6 kW of PV is not enough to adequately charge 1575 aH of batteries on a vehicle all year round. (Why do you need so much battery capacity? I hope you're not planning to heat water or the interior that way! One or two minisplit A/Cs won't need that much either.) That is about a 6% charge rate, barely above the minimum recommended. The NAWS gurus strongly recommend charging FLA batteries at between 5 and 13% of their 20-hour rate, and I would suggest aiming for the upper end of that range if it's on a bus where insolation and orientation isn't always ideal. You also have to think how well you can charge on a dull winter day when the sun is low and sets early. If you cannot charge your batteries to 100% every day they will end up being deficit-charged, and that will lead to their early demise. Imagine if you charge them to 98% each day: after just one week they are at about only 85% of their full charge, and a slow death is inevitable. This is why I have sufficient PV to charge at about 13%, so even in winter I can keep my banks fully charged.

Six of those batteries weigh about 750 pounds. That's a lot! That much weight needs some careful thought about W&B and location. Because they're not AGMs they will need regular watering and SG checks, so they will need to be on pull-out trays to do so. Making trays to handle that much weight will be an engineering challenge in itself, plus sufficient space must be maintained above them for ventilation and out-gassing when being charged. Why not just use good ol' golfcart batteries that are still the best bang for the buck in terms of dollars per watt, and they're readily available everywhere in case you need to replace any wherever you are.

As others here have mentioned, you need to think through your planned system carefully. As it stands now, it will work, sort of, but not well and not for long.

John

I really thought I had read somewhere (HandyBob?) that 10% was the goal? I can downsize the battery bank to somewhere around 1200ah.

That aside, golf cart batteries were originally the idea, but having more than 3 sets in parallel seems like it will give me less than stellar results. I could do two separate battery banks... but its going to cost more.

For boondocking purposes I’d like to be able to go at least a week if there’s minimal solar charging due to weather. Think Pacific NW.

[oredigger]

Originally Posted by Velocipedic

What is a HUGE battery bank then? I'm going to get six of these batteries which will put me at 1575ah, wired for 12V. I have 1.6kW of solar. I'm purchasing two charge controllers as you've listed above and similar cabling.

Originally Posted by Iceni John

The NAWS gurus strongly recommend charging FLA batteries at between 5 and 13% of their 20-hour rate

John

The 20-hour rate on those batteries is 395ah each. With 3 pair, that's 1185ah. 1575ah is the 100-hour rate.

[brokedown]

Another vote here for getting away from 12v. Everything gets easier when you double (or quadruple) your voltage. I've considered going to 24v myself and I'm only doing 400-500 watts of solar. Any higher and it would be a no brainer.

[Velocipedic]

Originally Posted by oredigger

The 20-hour rate on those batteries is 395ah each. With 3 pair, that's 1185ah. 1575ah is the 100-hour rate.

Cool! So I'm good on the 20-hr rate!

Originally Posted by brokedown

Another vote here for getting away from 12v. Everything gets easier when you double (or quadruple) your voltage. I've considered going to 24v myself and I'm only doing 400-500 watts of solar. Any higher and it would be a no brainer.

I found someone to take the 12V inverter at basically the same price, so I'll just purchase a new one at 24V and buy 24-12V stepdown circuits for the DC lights etc...