Adding an AC charger to 12V System

[rmaddy]

It was gonna be a 206ah SOK but I found I could get that extra 74ah for $300 less.

Does that take into account the BMS, bus bars, some sort of case, time and effort building, balancing, testing, etc.?

but will the 400w of panels suffice?

400W mounted flat on the roof may give you 360W for 5 hours on a perfect early summer day for about 1800Wh. That's about 50% of your 12.8V 280Ah battery (3584Wh). Most of the year you'll get less out of the panels. Driving or shore power could allow for extra charging when needed.

If I wire the panels in series, the amperage should still be 9.8A correct? Will the 100/15 suffice? 100/20? 100/30? Or should I just get the 100/50 in case I want to add a panel or 2? (down the road it's possible I remove the system to reinstall on another van, bus, or for a homestead, which may require a larger system, therefore a larger controller). Thoughts and suggestions?

400W / 12V = 33A of possible charge current. Though 360W at 13.5V = 27A. So a 100/30 would let you take full advantage of the 2 200W panels. If you add two more panels you would need 60A of charge current. That could be done by adding a 2nd 100/30 or upgrading to a 60A charge controller. Buying a 100/50 now would let you add a 3rd panel. You could add a 4th panel to a 100/50 but you wouldn't be able to make use of the full 800W. At best it would handle about 675W. And that's not actually too bad since you would rarely get much more than 675W out of the flat mounted panels much of the year.

 

[camelCase]

I can live with 400w and a DC-DC charger.

Ok, but if the Max Power Current of the panels is 9.8A and the panels are in series, doesn't that negate the capability of the mppt to charge at 30A since the panels can only push the 9.8A Max? Please explain. Thank you.

That's the magic of MPPTs. They reduce the voltage of the power coming from the solar panels without losing much of the current. If the MPPT takes in about 400w from the array at 30v and reduces the voltage to a little less than 15v but still passes most of that 400w to the batteries, that means about double the amps go into the battery as come in from the panels.

Amps = Watts/Volts
or switched around
Watts = Amps * Volts

 

[dudedogvan]

Does that take into account the BMS, bus bars, some sort of case, time and effort building, balancing, testing, etc.?


400W mounted flat on the roof may give you 360W for 5 hours on a perfect early summer day for about 1800Wh. That's about 50% of your 12.8V 280Ah battery (3584Wh). Most of the year you'll get less out of the panels. Driving or shore power could allow for extra charging when needed.


400W / 12V = 33A of possible charge current. Though 360W at 13.5V = 27A. So a 100/30 would let you take full advantage of the 2 200W panels. If you add two more panels you would need 60A of charge current. That could be done by adding a 2nd 100/30 or upgrading to a 60A charge controller. Buying a 100/50 now would let you add a 3rd panel. You could add a 4th panel to a 100/50 but you wouldn't be able to make use of the full 800W. At best it would handle about 675W. And that's not actually too bad since you would rarely get much more than 675W out of the flat mounted panels much of the year.

It takes the EVE cells from Docan Power and a 120A JBD Smart BMS into account. Bus bars and nuts come with cells. Cells already have studs. case will be made from recycled materials mostly (wood), I planned to just use the BMS over time to self balance (bad idea?), what would testing involve? Time was not taken into account. It sounds like you're making a case for just buying a 206ah SOK and moving forward.

Thanks for the rest of the info and explanation, very helpful.

That's the magic of MPPTs. They reduce the voltage of the power coming from the solar panels without losing much of the current. If the MPPT takes in about 400w from the array at 30v and reduces the voltage to a little less than 15v but still passes most of that 400w to the batteries, that means about double the amps go into the battery as come in from the panels.

Amps = Watts/Volts
or switched around
Watts = Amps * Volts

Gotcha, thanks

 

[dudedogvan]

Does that take into account the BMS, bus bars, some sort of case, time and effort building, balancing, testing, etc.?

Do you think it's unwise to jump right into a DIY LiFePO4 for my first system? Maybe get a system under my belt before I get so deep into something new? Get a 206ah SOK and get on with it?

 

[rmaddy]

It sounds like you're making a case for just buying a 206ah SOK and moving forward.

Just making sure you had taken everything into account. DIY saves you some money but it's a bunch more effort with the assembly, top balancing, capacity testing, etc. Buying a pre-built may cost a few more dollars but it just works (usually) and takes no effort. As long as you make your choice knowing all of the pros and cons then you can make that choice knowing it's best for you.

 

[dudedogvan]

Just making sure you had taken everything into account. DIY saves you some money but it's a bunch more effort with the assembly, top balancing, capacity testing, etc. Buying a pre-built may cost a few more dollars but it just works (usually) and takes no effort. As long as you make your choice knowing all of the pros and cons then you can make that choice knowing it's best for you.

I appreciate your realistic perspective. I think it would better suit me to consider the pre-built. I may be getting a bit ahead of myself jumping right into a diy build when I'd just like it to work and move on with building the van.

 

[rmaddy]

Do you think it's unwise to jump right into a DIY LiFePO4 for my first system? Maybe get a system under my belt before I get so deep into something new? Get a 206ah SOK and get on with it?

That's a personal choice. Plenty of first timers build their own.

 

[rmaddy]

I may be getting a bit ahead of myself jumping right into a diy build when I'd just like it to work and move on with building the van.

I spent 18 months converting my cargo trailer into a camper. I bought pre-built batteries because I didn't want to spend the time and effort, on top of everything else, doing a DIY battery. But that was my choice for me. If you would rather work on your van, buy the SOK. If you want the additional challenge of doing a DIY battery, go for it.

 

[smoothJoey]

I know 600w would be optimal, but will the 400w of panels suffice?

I will defer to others for the pv questions.

Roughly, this equates to 400w panels charging the batteries to a ~70% SOC (following the simple rule: panel wattage=2X battery ah).

I've not heard of that rule.

With my logic the EVE cells will remain healthy because they have no issue with being partially discharged consistently, correct?

Almost all EVE cells are sold as Grade A.
There are only 2 suppliers that I'm aware of that supply anything like grade A cells.
If you have grade B cells(like me) or worse, they generally need to be charged into the high knee regularly so that the BMS can maintain the top balance. Some of the crappier cells need an active balancer to keep the cell drift manageable.

Or am I way out there? If my power needs ever increase, I will already have invested in the extra 74ah capacity and saved money. Logically, it seems like best use of my resources.

What is your planned system voltage?
280ah @ 12.8 volts = 3584 watt hours
280ah @ 25.6 volts = 7168 watt hours
280ah @ 25.6 volts = 14336 watt hours

I also plan to have a DC-DC charger to supplement when driving. The van's alternator is 115A and the starter battery is a FLA 650CCA.
Is a 20A DC-DC charger what I need? 30A? 40A? suggestions please.

Depends on how much excess alternator capacity you have.
A smaller dc2dc charger is safer.

Looking at Victron SmartSolar mppt, the 200w Rich Solar panel specs are:

• Maximum Power(Pmax): 200W
• Maximum Power Voltage(Vmp): 20.4V
• Maximum Power Current(Imp): 9.80A
• Open Circuit Voltage(Voc): 24.3V
• Short Circuit Current(Isc): 10.2A
• Maximum System Voltage(Vmax): 1000VDC

If I wire the panels in series, the amperage should still be 9.8A correct? Will the 100/15 suffice? 100/20? 100/30? Or should I just get the 100/50 in case I want to add a panel or 2? (down the road it's possible I remove the system to reinstall on another van, bus, or for a homestead, which may require a larger system, therefore a larger controller). Thoughts and suggestions?

I will defer to others for the pv questions.

 

[smoothJoey]

my power audit yields an estimated peak power demand of ~145ah/day

That is just slightly more than 50% depth of discharge per day.
Another way to think about it is 1 extra day of autonomy.

I would plan for charge capacity of greater than 145ah per day.

145ah * 12.8 volts nominal = 1856 watt hours.

400 watts solar * .5 flat mount penalty * .9 conversion efficiency = 180 watts per hour of sunshine.

That means you would need over ten hours of sunshine to make your nut each day.
Hopefully one of the pv wizards will check my napkin math.

How much driving do you plan to do each day?
How much shore power availability are you planning for?

 

[dudedogvan]

I spent 18 months converting my cargo trailer into a camper. I bought pre-built batteries because I didn't want to spend the time and effort, on top of everything else, doing a DIY battery. But that was my choice for me. If you would rather work on your van, buy the SOK. If you want the additional challenge of doing a DIY battery, go for it.

I've settled on buying a prebuilt 206ah SOK. I need to move on with the build and if I'm being honest with myself, I don't really want to fool with building a DIY (maybe later in my DIY solar journey).

I've not heard of that rule.

It's a beginner concept one will find in many of the van build electrical resources on youtube and the rest of the internet. It aims to simplify choosing battery and panel sizes for beginners. As stated, if one determines they need a 200ah battery bank, a recommended panel array to charge 200ah would be 2X that or 400w. To my knowledge, it doesn't take flat mounting or conversion efficiency into account. When one takes flat mounting and conversion efficiency into account (reality), the losses paint a different picture of what's actually needed to meet demands.

What is your planned system voltage?
280ah @ 12.8 volts = 3584 watt hours
280ah @ 25.6 volts = 7168 watt hours
280ah @ 25.6 volts = 14336 watt hours

I'm gonna do a 206ah SOK 12V system= 2636.8wh

Depends on how much excess alternator capacity you have.
A smaller dc2dc charger is safer.

115A alternator.

How much driving do you plan to do each day?
How much shore power availability are you planning for?

I cannot accurately say how much driving I will do. It will vary so IMO it's best to just size a DC-DC charger based on the alternator and have that option available.

jbird526 suggested this:

To supplement your solar you could put together your own portable foldable panels using 2 100 watt panels and laying them out on a lean to. Another solar controller to add but does not have to an expensive unit as this may just be used intermittently.

I like this idea, allows me to supplement roof panels when parked if needed. Based on calculations above with losses, the reality sounds like I may want to do the 400w roof panels and supplement with 200w of foldable panels and cheaper mppt when parked.

 

[HRTKD]

Very few people will complain about having too much PV power. If 400 watts is all you can fit, then that's what you're going to install on the roof. Need more PV power? Deploy a couple more panels on the ground, going into a second solar charge controller. That's what I do and it works great for me. Some trips I leave the ground deployed panels at home because I know I won't need them.

A standard 30 amp RV connection on the side of the van, with an appropriate cord, would come in very handy if you needed to overnight at a campground with hookups. That same connection could also be used if you get a portable generator later on. The 30 amp RV connection, in my mind, is a way to future-proof your system.

Your alternator is kind of small. I would be very conservative on the size of the DC-DC charge that you go with. The rating is on the output side, not the input side. A 20 amp DC-DC charger may pull 30 amps (probably not, more like 25) and you have to put in sufficiently large cabling to handle that 30 amps over the distance. That can get expensive!

 

[smoothJoey]

115A alternator.

You already said that.
We need to know how much of that capacity your vehicle is already using so that we can figure how much the charger can use.

 

[rmaddy]

A standard 30 amp RV connection on the side of the van, with an appropriate cord, would come in very handy if you needed to overnight at a campground with hookups. That same connection could also be used if you get a portable generator later on. The 30 amp RV connection, in my mind, is a way to future-proof your system.

I'll add that with a simple adapter cord you can also use the 30A RV connection on the side of the van to plug into a standard 15A outlet at someone's house with a sufficient extension cord. So the 30A shore power plug gives you a lot more flexibility with no additional effort.

 

[dudedogvan]

You already said that.
We need to know how much of that capacity your vehicle is already using so that we can figure how much the charger can use.

From what I gather, the way to measure this accurately is to measure the output current of the alternator with the vehicle parked and revving the engine up to 1500-2000 rpm. Then I'll know how much current the alternator already pushes to charge the starter battery, correct?

Another consideration is the max charge current of the 206ah SOK: 50A
If the max current output of the victron 100/30 mppt is 30A, the battery can only accept another 20A so isn't a 30-40A DC-DC charger unnecessary? Or say the charge controller is only putting out 10A due to low sunshine, having a higher Amperage DC-DC charger (say 40A) working safely within the alternator's leftover capacity (what's not being drawn to charge the starter battery) will be more equipped to fulfill the 50A max charging current of the 206ah SOK, right?

Which brings me to a concept I'm still struggling to understand: If the recommended max charge voltage of the 206ah SOK is 14.6V, how is there no conflict between multiple charging sources (panels w/ mppt, DC-DC charger, and inverter/charger)? How do the components safely work concurrently without conflict or damage to the system? In discussing this with my father, I am unable to explain how/why it all works together without issues, I need to understand this concept.

First off multiple charging sources are generally not an issue. Each will have a maximum charging voltage and will stop when that voltage is reached. Having multiple sources will not push the voltage higher than any of the chargers is programmed.

Is this an RV? Van conversion? If you add an inverter and want to connect to the existing 120v system a transfer switch is needed and will select power from the main cord or the inverter. Generally inverter-chargers will have a built in transfer switch. If no inverter is being installed then no transfer switch is needed.

No need to turn off solar or the charger while driving and charging through the DC-DC charger. These all can operate together or separate depending on which have a power source to charge. BMS is the last stand of safety to protect the battery. The various chargers should never trip the BMS even when used together.

How/why?

In this thread, time2roll comments: "Multiple loads and multiple charging sources are good to all run concurrently. No issues."
Please explain how/why this is? I'm not trying to be dense here, still just a newb trying to understand something totally new to me.
Once again, I want to express my gratitude to everyone taking their time to help me understand!

 

[smoothJoey]

From what I gather, the way to measure this accurately is to measure the output current of the alternator with the vehicle parked and revving the engine up to 1500-2000 rpm. Then I'll know how much current the alternator already pushes to charge the starter battery, correct?

Its not just the starter battery its all the loads that run off the chassis alternator.

Another consideration is the max charge current of the 206ah SOK: 50A
If the max current output of the victron 100/30 mppt is 30A, the battery can only accept another 20A so isn't a 30-40A DC-DC charger unnecessary?

You do need to make sure that the aggregate charge current does not exceed 50 amps.

Which brings me to a concept I'm still struggling to understand: If the recommended max charge voltage of the 206ah SOK is 14.6V, how is there no conflict between multiple charging sources (panels w/ mppt, DC-DC charger, and inverter/charger)? How do the components safely work concurrently without conflict or damage to the system? In discussing this with my father, I am unable to explain how/why it all works together without issues, I need to understand this concept.

The voltage is not additive.

 

[smoothJoey]

This document although it doesn't address multiple charge sources may help you understand how charging works.

How charging works in the context of LFP batteries

How charging works in the context of LFP batteries

diysolarforum.com

 

[rmaddy]

Another consideration is the max charge current of the 206ah SOK: 50A

One way to work around this limitation is to have multiple batteries in parallel. You could put 2 12V 100Ah SOK batteries in parallel to get a 12V 200Ah system that can accept 100A of charge current. Or 2 12V 206Ah in parallel for a 12V 412Ah system that also accepts 100A of charge current. Or, since you originally thought of a 280Ah system, put 3 12V 100Ah batteries in parallel for 12V 300Ah that accepts 150A of charge current.

 

[time2roll]

How/why?

In this thread, time2roll comments: "Multiple loads and multiple charging sources are good to all run concurrently. No issues."
Please explain how/why this is? I'm not trying to be dense here, still just a newb trying to understand something totally new to me.
Once again, I want to express my gratitude to everyone taking their time to help me understand!

Each charging source has a voltage limit. As the battery voltage rises the charging source stops charging when the battery voltage matches the charging voltage.

Say the alternator is charging at 14.2 volts and 20 amps. At the same time the solar is charging at 14.4 volts and 10 amps. The battery is at 13.3 volts in the early morning as the van starts to roll to the next destination. Both sources will charge giving 30 amps total (alt 20 + solar 10). This will continue until the battery voltage rises to 14.2 volts and the alternator stops putting energy into the battery. The solar continues at 10 amps until the battery hits 14.4 volts and the solar shuts down also. All this happens automatically and the battery is full charge as the van arrives at the next destination.

Once a few trips are made this will all seem easy.

 

[jbird526]

@dudedogvan In another thread you mentioned you had an 2004 Ford E150 Passenger van. That is a rather "dumb" alternator, compared to say a new Sprinter vans variable voltage, ECU controlled unit. If you don't mind wrenching and spending another @$250 you could swap out the alternator with say a 200 amp and have no concerns about DC to DC limits. You could add 2 30 amp Orions or 1 60 amp Sterling. I know all that isn't cheap though. Also have to account for the additional wiring, which depending on amperage can get costly over a distance.

That is all theoretical as I have not actually wired up large DC to DC units but something to investigate.

I always hated working on vans due to the packaging but if I remember on those, the alternator is on top of the engine under the air intake and fairly easy to access?