diy solar

diy solar

NEWB going from 12v to 24v

Would keeping the 30amp charger I am currently using work until I get the LiFePO4 set up instead?
I would recommend installing the new charger if you can:

1) Limit the amp output with an SCC setting. My Victron does this,
2) Limit solar panels so you get no more than 20 amps.

With the 30 amp charger and FLAs, you could still over charge, so the same two items above will apply.

WIth data you have already, going from 12 to 24 wattts with the same panels will produce just as many watts, but at twice the volts and half the amps. For me, once I get the 24 volts set up with the current 4 X 6 volt golf cart batteries, I’ll get some data before I drop in a much bigger lithium battery.
 
Oh no. Ok, I havent switched to the LiFePO4 yet but am planning on it. Sounds like I should just do it all at once with the new system.

I currently have a converter to charge the batteries off the generator, and understand the calculation to figure this out for 12v, but I'm not sure how to calculate for 24v in case I now need a larger converter to charge the batteries in the winter with periods of no sun? For these12v, the battery data sheet says 30A charge rate, and in parallel it would be 30Ax4=120A but would it only be 60A for the 2 strings of batteries of 2 in series of 100ah 12v?

OK.... looks like you are ok after-all, Yes. In your 2x2 battery arrangement, if the batteries can take 30A individually, your total charge rate is 60A
That means your 60A controller is at the topend of what your batteries can take but still OK.
I currently have a converter to charge the batteries off the generator, and understand the calculation to figure this out for 12v, but I'm not sure how to calculate for 24v in case I now need a larger converter to charge the batteries in the winter with periods of no sun? For these12v, the battery data sheet says 30A charge rate, and in parallel it would be 30Ax4=120A but would it only be 60A for the 2 strings of batteries of 2 in series of 100ah 12v?
Does your current converter have the ability to charge 24V banks? What make/model do you have.

Also, if you use the generator/converter to charge at the same time as solar, you will exceed the 60A charge rate.

Would keeping the 30amp charger I am currently using work until I get the LiFePO4 set up instead? ?
Thank you all for your help. These calculations are not my area of expertise (clearly). I'm more of a practical application type of gal but this is all necessary evil (for me) to get it right.
Everything sounded fine, even with Lead Acid till the converter got thrown in the mix. One way to deal with this is to never use solar and the converter at the same time (and make sure the converter does not exceed 60Amp. THe other way is to make sure the combination of converter and solar never goes above 60A.

You can still keep the 60A charger, but if you need it to produce less current, put fewer panels on it. (I would still wire for 9 panels.... just don't populate them all till you have LiFePO4. )
 
I would recommend installing the new charger if you can:

1) Limit the amp output with an SCC setting. My Victron does this,
2) Limit solar panels so you get no more than 20 amps.

With the 30 amp charger and FLAs, you could still over charge, so the same two items above will apply.

WIth data you have already, going from 12 to 24 wattts with the same panels will produce just as many watts, but at twice the volts and half the amps. For me, once I get the 24 volts set up with the current 4 X 6 volt golf cart batteries, I’ll get some data before I drop in a much bigger lithium battery.
Ah, ok that makes sense. So you'll get to see how it runs before dropping in the new batteries. So I could do 2 strings in parallel of 3 in series which would give me 16.74A and 70.8V then hook the third string up when the Lithium batteries arrive.
 
OK.... looks like you are ok after-all, Yes. In your 2x2 battery arrangement, if the batteries can take 30A individually, your total charge rate is 60A
That means your 60A controller is at the topend of what your batteries can take but still OK.

Does your current converter have the ability to charge 24V banks? What make/model do you have.

Also, if you use the generator/converter to charge at the same time as solar, you will exceed the 60A charge rate.


Everything sounded fine, even with Lead Acid till the converter got thrown in the mix. One way to deal with this is to never use solar and the converter at the same time (and make sure the converter does not exceed 60Amp. THe other way is to make sure the combination of converter and solar never goes above 60A.

You can still keep the 60A charger, but if you need it to produce less current, put fewer panels on it. (I would still wire for 9 panels.... just don't populate them all till you have LiFePO4. )
Perfect! Thank you! That's great to know. So I can just switch off the panels if I need to run the converter?
 
Ah, ok that makes sense. So you'll get to see how it runs before dropping in the new batteries. So I could do 2 strings in parallel of 3 in series which would give me 16.74A and 70.8V then hook the third string up when the Lithium batteries arrive.
Yup.... something like that will work. If the charge controller can be set to limit the current then do all the panels but throttle the charge controller output using the settings.

However, keep in mind that the current we are talking about is the output current of the charge controller, not the current from the panels.

If you have two strings of 3, you will still have a total of 6x285W = 1710 watts. Coming out of the charge controller you could still have the full 60A . (If you recall, I calculated 6 to be kinda the most without over-panneling)
 
OK.... looks like you are ok after-all, Yes. In your 2x2 battery arrangement, if the batteries can take 30A individually, your total charge rate is 60A
That means your 60A controller is at the topend of what your batteries can take but still OK.

Does your current converter have the ability to charge 24V banks? What make/model do you have.

Also, if you use the generator/converter to charge at the same time as solar, you will exceed the 60A charge rate.


Everything sounded fine, even with Lead Acid till the converter got thrown in the mix. One way to deal with this is to never use solar and the converter at the same time (and make sure the converter does not exceed 60Amp. THe other way is to make sure the combination of converter and solar never goes above 60A.

You can still keep the 60A charger, but if you need it to produce less current, put fewer panels on it. (I would still wire for 9 panels.... just don't populate them all till you have LiFePO4. )
I'll have to get a new converter for the 24v system, our current one will only work on the 12v. We typically only run it at night when we didn't have enough sun during the day. The 24v Converters come in 25A, 30A, 40A and 50A but those all sound too high for the current battery bank, keeping it under 20A.
 
So I can just switch off the panels if I need to run the converter?
Yes..... but make sure you remember to do it!!!! Also, if the sun is shining, there is really no benefit to running the converter. Just let the panels do the work. Where the converter will make sense is when the sun isn't shining.
 
Yup.... something like that will work. If the charge controller can be set to limit the current then do all the panels but throttle the charge controller output using the settings.

However, keep in mind that the current we are talking about is the output current of the charge controller, not the current from the panels.

If you have two strings of 3, you will still have a total of 6x285W = 1710 watts. Coming out of the charge controller you could still have the full 60A . (If you recall, I calculated 6 to be kinda the most without over-panneling)
Ah, I gotcha. OK. Hopefully I can change the output on the controller. If it doesnt have that option, would doing panels in parallel make more sense until the lithium batteries arrive?
 
Yes..... but make sure you remember to do it!!!! Also, if the sun is shining, there is really no benefit to running the converter. Just let the panels do the work. Where the converter will make sense is when the sun isn't shining.
Ha yes, that will be the key! Typically the case anyway. Evening when we didn't get enough sun during prolonged periods of rain, etc. We're slowly upgrading to hopefully not need it hardly at all, thankfully.
 
I'll have to get a new converter for the 24v system, our current one will only work on the 12v.
There is one use for the 12V converter: Before you wire the batteries in the 24V, 2x2 configuration, wire them in parallel (12V) and fully charge them till it goes into float. That way when you put them in series they will be balanced.

The 24v Converters come in 25A, 30A, 40A and 50A but those all sound too high for the current battery bank, keeping it under 20A.
As long as you don't run the converter and solar at the same time on your lead acid batteries, any of the above will work.... just some faster than the others.

EDIT: Added the following sentence:

When you buy the converter, buy for what you will want with LiFePO4. When you go to LiFePO4 you should size things such that you don't have to worry about running the solar and converter together.


I like to keep the charge rate for LiFePO to .5C or less. Depending on what you do for LiFePO, the size converter you can use will vary.
As an example, if you have 200Ah of LiFePO, .5C is 100A. With the 60A of the solar, the largest converter you should use is 40A (60+40=100)
However, if you build your own battery out of 280AH cells, .5C is 140A and the 50A converter would be usable.
 
BTW: have you bought your 24V inverter yet? You may want to consider getting an inverter-charger that can both charge the battery and power your AC.
 
BTW: have you bought your 24V inverter yet? You may want to consider getting an inverter-charger that can both charge the battery and power your AC.
Ugh, yes, unfortunately. We've had it for a while waiting to be put to use but that would have been a better thing to do. ?‍♀️
When we upgrade to the LiFePo4, we really shouldn't need the converter with the system size upgrade, but it's probably still good to have on hand just in case. With the lead acid batteries, it's been more of a concern, making sure they stay above 50%.
 
Ugh, yes, unfortunately. We've had it for a while waiting to be put to use but that would have been a better thing to do. ?‍♀️
When we upgrade to the LiFePo4, we really shouldn't need the converter with the system size upgrade, but it's probably still good to have on hand just in case. With the lead acid batteries, it's been more of a concern, making sure they stay above 50%.
Will you have a transfer switch that allows you to run your AC of the Generator instead of the inverter? That is always a very handy fallback and, if it is truly rare that your LiFePO upgrade will require the converter, maybe you just use the generator in those situations and not have the inverter.

Having said that, it is very nice to be able to charge the batteries from the generator as well.
 
BTW: With the 50% over-paneling we are discussing, you will very likely get a fair amount of solar power even on cloudy days. Furthermore, your power production will ramp up to the full 60A earlier in the day and keep going till later in the day. Proof will be in the pudding, but it sounds like your in a southern area so your Insolation number will be higher to start with and with the extended production due to over-paneling, you could see as much as 8KWh of production on a sunny day.
 
Will you have a transfer switch that allows you to run your AC of the Generator instead of the inverter? That is always a very handy fallback and, if it is truly rare that your LiFePO upgrade will require the converter, maybe you just use the generator in those situations and not have the inverter.

Having said that, it is very nice to be able to charge the batteries from the generator as well.
So far, it just runs directly off the generator but yes, a transfer switch is in the plan. We've bypassed the inverter to the generator anyway for the bigger tools and appliances. It's nice to have as a backup regardless but it'll be nice to be more efficient in the long run
BTW: With the 50% over-paneling we are discussing, you will very likely get a fair amount of solar power even on cloudy days. Furthermore, your power production will ramp up to the full 60A earlier in the day and keep going till later in the day. Proof will be in the pudding, but it sounds like your in a southern area so your Insolation number will be higher to start with and with the extended production due to over-paneling, you could see as much as 8KWh of production on a sunny day.
This will be awesome! I really appreciate the guidance. This morning, I was about ready to pull my hair out after days of doing the math and calculations but still going in circles with my lack of understanding. Upholstery and ranching are my expertise, but this is really a whole different world. We're in California so definitely get a fair amount of sunshine, now finger's crossed I can make it happen how it is on paper ?
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