RV 24V system New

[johnprice752]

Hi. Looking to build RV 24v system using 8 off 280a lifepo4 cells solar will be from 2 off 250w 30v 8a panels laid flat. Quistions 1 is a BMS vital if i do a bottot and top to start with.
2 is the top voltage cut of important as thinking of using my solar controller that doesn't have one. Lastly where best to get a 24v to 12v converter. Currently in Spain.
Thanks in advance john

 

[GSXR1000]

I would go with this. and you can can parallel them if you need more current

 

[johnprice752]

Hi. thanks will need that for the 12v services.
Just wondering how important the BMS actually is. ?

 

[HRTKD]

Yes, you need a BMS.

My opinion is that for most RV, 24v is overkill. If you need an inverter that is rated for more than 3000 watts then 24v is warranted.

 

[johnprice752]

Hi,
I have just ordered a daly 8s bms. 150a. will be running a 3000/6000 inverter in an all electric RV conversion.
hope i have enough solar but more to the point. Enough skill to get it working correctly.
i'm sure i will be back here looking for guidance.
thanks

 

[Alkaline]

I am using this, it works well and has no amp draw when idle

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you can also parallel them.

 

[Rocketman]

Yes a BMS is vital when using lithium batteries. - especially when on a RV.

 

[johnprice752]

Do i wire my 2 solar panels in series or parallel. am i right in thinking Series would be 60v 250w 16a & parallel would be 30v 500w 16a. theoretical.
as i say i may be back

 

[johnprice752]

Yes a BMS is vital when using lithium batteries. - especially when on a RV.

hint taken, ordered and eager to start building when the parts arrive. fingers crossed

 

[HRTKD]

I am using this, it works well and has no amp draw when idle

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you can also parallel them.

I looked up that part number and it shows a 70 mA idle draw.

https://www.ato.com/Content/doc/dc-dc-converter-24v-to-12v/ATOWG-24S1240.pdf

 

[HRTKD]

Do i wire my 2 solar panels in series or parallel. am i right in thinking Series would be 60v 250w 16a & parallel would be 30v 500w 16a. theoretical.
as i say i may be back

Series would be 60v but only 8 amp. Series = volts add. Parallel = amps add.

 

[Rocketman]

For solar panels - No think of it as
1-by itself 30v 8.3 amps
2- in series 60v 8.3 amps
2- in parallel 30v 16.6 amps

 

[johnprice752]

So parallel or series into a 20a solar controller? looking at a low end controller as I don't intent looking at it to often. as per WILLS controller comparison youtube vid

 

[johnprice752]

I'm thinking its between the top and bottom one, your thoughts ?

 

[HRTKD]

The amp rating of a solar charge controller is the output, not the input. Make sure the voltage of your panels does not exceed the input voltage of the controller. There isn't enough info in the titles of those listings to know.

Many of the super cheap MPPT controllers aren't actually MPPT but are PWM. The sellers just say they're MPPT. I can't say one way or the other on those listings, but the one that doesn't have MPPT in the title is likely to be PWM.

 

[Alkaline]

well it shows 0 watts on my setup when its not doing anything this is based on the output from my shunt.

Even though 70ma its pretty reasonable if that is the case, that is 20 watts/day

 

[Goodoz]

Yes, you need a BMS.

My opinion is that for most RV, 24v is overkill. If you need an inverter that is rated for more than 3000 watts then 24v is warranted.

I would be 100% more sure footed in my TT opinions if I could see under my TT...like most, it's enclosed and has never been off. I'll take a few hundred pics when that happens...in a few weeks. That said, I like the higher volts and smaller gauges for wire fishin' purposes...but even that might not be a concern if I could see the underbody!

 

[johnprice752]

Hi . Decided on and received my Daly BMS. 8s 24 v 150a. 2 solar panels fitted. 37v 250w 8a. Thinking of wiring them in parallel . 37v 16a.
Waiting eagerly for the batteries to arrive.

 

[koobs]

Hi . Decided on and received my Daly BMS. 8s 24 v 150a. 2 solar panels fitted. 37v 250w 8a. Thinking of wiring them in parallel . 37v 16a.
Waiting eagerly for the batteries to arrive.

Solar panel wiring depends on what solar controller you get. MPPT vs PWM. For a PWM controller wire the panels in parallel, as it cuts off anything above the desire battery voltage anyhow.
For MPPT controllers, say it has a 100V limit, then you can wire two panels in series effectively.

 

[mkaye]

wiring series/parallel does not drive MPPT vs PWM directly
series = lower amps, smaller wire
parallel = higher current, larger wire
as long as you don't exceed the input voltage requirements of the SCC then either will work
a PWM SCC should be cheaper & in real life the efficiency difference isn't enough to get excited about

another consideration for series/parallel solar panels is panel shading
it only takes a small bit of shade to reduce a panel to a fraction of it's output
if in series then the other panel takes the same hit
if parallel the 2nd panel will have full output