Inverter/Charger/ DC to DC charger Confusion

[John Frum]

Ok so where do I go from here given that we can only deliver 100 amps continuous?

100 amps * 12 volts low cutoff * .85 inverter conversion efficiency = 1,020.00 ac watts.
You could use a 1000 inverter.
Or... you could buy 4 batteries is 2s2p configuration which would allow a 2000 watt inverter.

 

[HRTKD]

Before you go down the 24 volt system rabbit hole, I'll play Devil's Advocate. What is the voltage of the components that you're installing in the bus? Most of the off-the-shelf RV components that are readily available are 12 volt. Some can do 12 or 24 volt.

The size of your inverter is directly related to the size of your AC loads. What are your heaviest AC loads?

I'm not ruling out a 24 volt system. Since this is a greenfield implementation, you don't have to work around existing 12 volt components. I'm just pointing out that you should do your research to verify that 24 volt components/appliances are in stock and not on back order for months on end. The supply chain is crazy right now and the more you stray from the norm the more likely it is you'll run into issues.

As long as you don't have high amperage 12 volt loads, you can get by with a standard 24-12 volt step down converter.

 

[crccrkc1995]

Everything we've purchased is 12v and we were planning to do the 24-12v step down converter.

 

[John Frum]

Everything we've purchased is 12v and we were planning to do the 24-12v step down converter.

With those batteries in series you could do a nice little system with a 2000 watt inverter and be just under the limit for a jbd 8s 100 amp bms.

 

[DerpsyDoodler]

With those batteries in series you could do a nice little system with a 2000 watt inverter and be just under the limit for a jbd 8s 100 amp bms.

Or you could continue with your plan, limit your inverter output, and consider yourself future-proofed for upgrading your battery bank. You can essentially grow into the inverter when you're ready to purchase another set of 12v batteries to add in parallel.

 

[crccrkc1995]

Yes, we are looking to the future and possibly adding batteries if needed. We just don't want to have to replace our Inverter, we'd rather "grow into it" or at least have the capability to grow into it.

 

[John Frum]

Or you could continue with your plan, limit your inverter output, and consider yourself future-proofed for upgrading your battery bank. You can essentially grow into the inverter when you're ready to purchase another set of 12v batteries to add in parallel.

Or you could weld the fets in your bms shut by over driving the bms and possibly having it disconnect under heavy load.
Once the fets are welded shut you probably won't know there is an prolblem until the bms fails to protect your cells from a low voltage "excursion".

 

[crccrkc1995]

So with that being said, would you recommend a 2000 or 3000w Inverter charger, there's not that much difference in price and paying for thicker wire doesn't really matter to me at this time.
And welding anything shut is not going to happen, lol.

 

[John Frum]

And welding anything shut is not going to happen, lol.

No disrespect but based on your questions I doubt you know what is possible and what isn't.
2000 watts is the safe option.
3000 watts is not as safe.

 

[DerpsyDoodler]

Or you could weld the fets in your bms shut by over driving the bms and possibly having it disconnect under heavy load.
Once the fets are welded shut you probably won't know there is an prolblem until the bms fails to protect your cells from a low voltage "excursion".

I guess you missed the part about limit your inverter output. Would you like to reread what I posted? A quality inverter, like my samlex EVO, for instance, has a plethora of configuration options, including imposing an output cap.

 

[John Frum]

I guess you missed the part about limit your inverter output.

I did.

 

[DerpsyDoodler]

I did.

Lol, poop happens.

 

[John Frum]

Its my policy to design for the full capacity of the inverter but I do acknowledge that there is more than one way to skin the cat.

 

[crccrkc1995]

No disrespect taken. I'm not an electrician or an electrical engineer and am trying to learn, that's why I'm talking to to people who obviously know more than I do. I've learned a bit and will continue to try. Thanks very much for taking all your time with me.

 

[schmism]

Its my policy to design for the full capacity of the inverter

You always assume the person is going to run it a full capacity. There will never come a time when the mindset of we installed a 3kw inverter but only going to use 1500w. and then someone has both the micro and the coffee maker on at the same time and you have to add your build to

Up in smoke... learn from my mistake!

Did your experimental battery or home built inverter experience a rapid, unplanned disassembly? Reverse polarity a $3K inverter, and see it go up in smoke? Share it here!

diysolarforum.com

as to the question at hand. if your considering 24v for 3kw then I say move to 48v (your still going to need a dc to dc converter for 24v just pick the one for 48v instead). sure you have to double your batteries to 4 instead of 2 but seems like you could use the extra capacity. (and it lowers your current draw from the battery) 3000w/48v = 62a <- now within spec for the battery previously listed

 

[John Frum]

No disrespect taken. I'm not an electrician or an electrical engineer and am trying to learn, that's why I'm talking to to people who obviously know more than I do. I've learned a bit and will continue to try. Thanks very much for taking all your time with me.

Personally I really don't trust these FET based BMS.
Its a crap design but the proper architecture is expensive.
They could do it properly for less money then what we pay now, but then the design would be too scalable to stratify the market.
So we live with a compromise.

 

[DerpsyDoodler]

You always assume the person is going to run it a full capacity. There will never come a time when the mindset of we installed a 3kw inverter but only going to use 1500w. and then someone has both the micro and the coffee maker on at the same time and you have to add your build to

Up in smoke... learn from my mistake!

Did your experimental battery or home built inverter experience a rapid, unplanned disassembly? Reverse polarity a $3K inverter, and see it go up in smoke? Share it here!

diysolarforum.com

If you configure the inverter to limit output, then its "new limit" would be its capacity. these settings and options in the higher tier inverters are meant for these purposes. There is nothing to argue here. Future-proofing is a thing, and part of proper design.

 

[John Frum]

If you configure the inverter to limit output, then its "new limit" would be its capacity. these settings and options in the higher tier inverters are meant for these purposes. There is nothing to argue here. Future-proofing is a thing, and part of proper design.

The folks who are asking these questions are buying old discrete inverters with minimal configurability.
I've been here long enough to see how many come back after 12-18 monthes looking to do it right the second time.

 

[DerpsyDoodler]

If you configure the inverter to limit output, then its "new limit" would be its capacity. these settings and options in the higher tier inverters are meant for these purposes. There is nothing to argue here. Future-proofing is a thing, and part of proper design.

In fact, if i look through my inverters settings agin, i think i can limit its output as well as what it will draw from the batteries, among a plethora of other things.

 

[DerpsyDoodler]

The folks who are asking these questions are buying old discrete inverters with minimal configurability.
I've been here long enough to see how many come back after 12-18 monthes looking to do it right the second time.

so if youre going to assist in design, why not help curb that problem with future-proofing? If they turn away from it, that's their problem.

In this case, OP was clearly interested in the idea.