diy solar

diy solar

Newbie with a PIP 2724LV-MR also a question about AC input, and batteries

M

Motormouth

New Member
Joined
Sep 16, 2023
Messages
18
Location
Virginia, US
I want to experiment with making a small starter system that I can use as an UPS
My neighborhood has had at least 5 multi-day outages in the last 20 years, which is very inconvenient.
I have a whole house back up generator, with a manual transfer switch, it works well but as you know you temporarily lose power with this configuration

Right now I have a couple APC UPS which work ok, but have very limited capacity.
For this build, solar is a nice to have but not the primary use of the system, rather I want to be able to backup all my network equipment, ie routers, switch, nas, maybe a refrigerator or two.

So after looking some of Will's and Ian's (Watts 247) videos ended up ordering a MPP Solar 2724LV-MR, it has AVR capability

I want make something similar to what is on this youtube video:

So two questions,

Question 1) one for the AC input to the 2724LW-MR the manual suggests a 40 amp direct wiring. I would like use a 30 amp plug (ie a TT30 or nema L5-30) so that I can hook it up to my 3500 W inverter generator or use a 30 amp outlet let that I would install in the house
Do I need to go up to a 50 amp plug or will the 30 amp be sufficient (ie the all in one is 2700 watts or 2700Watts/120v = 22.5 amps)? or is 40 amp wiring that critical for things like surge?
Both Will and Ian wired theirs up with 15 amp lines on their demo videos.

Question 2) Batteries, the manual suggested at leat 100ah batteries (ie I was thinking two 12.8 V 100ah batteries, but these usually have 100 amp BMS), will this be enough? If, the batteries only have 100 amp BMSes, that would only be 2400 Watts they could pull, and the unit is 2700 watts. Do I need to find batteries with at least 120 amp BMSes? or can I get away with the more common 100 amp BMS batteries out there. Larger capacity batteries usually have larger BMS, (but not always) and some times lower capacity batteries have small BMSes, again not always. What are your thoughts?

Eventually I will need to replace my roof, in about 3-5 years, and want to be ready to go big, ie SolArk 15K or 18K EG4/luxpower, or what ever else is out at that time and 20+ KWh batteries, etc. At that point I will use this little system in my little cabin.
 
Last edited:
Motormouth said:
Batteries, the manual suggested at leat 100ah batteries (ie I was thinking two 12.8 V 100ah batteries, but these usually have 100 amp BMS), will this be enough? If, the batteries only have 100 amp BMSes, that would only be 2400 Watts they could pull, and the unit is 2700 watts
Click to expand...
EDIT: Not enough coffee in me, I musta been smoking something. ?

FWIW finding 12v batteries with a 200a BMS is ALMOST as hard as finding a 200a BMS for your 24v 8s DIY setup. Only JK and Daly seem to have them, no love finding them in JBD (or clones) or Overkill. They're out there but a 24v with a 200a is much easier to find in pre-builts.
 
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Rednecktek said:
30a plug will be fine, and you're better off getting a straight 24v battery with a 200a BMS which is a pretty common battery.
Click to expand...
Thanks for the fast reply. The 30a plug seemed to make sense to me.

As for your second comment, I think my math is correct, ie two 12.8 V 100ah with 100 amp bms in series would be 25.6V 100ah limited to 100 amp bms discharge. the100 amp BMS is limiting current not the series voltage ie it would still be 24volts x 100 a = 2400 watts.

1200 watts would be what you would get from a single 12v 100 amp bms. ie or 12 volts x 100a = 1200 watt.

the current would be limited by the lowest bms current, ie if you had two 12 v batteries in series, one with a 200 amp bms and one with a let us say a 80 amp bms. the current would be 80 amp max so you would get a 24v x 80 amps or 1920 watts.

In series the current is limited by the lowest current bms, but the voltage is additive, if both batteries have 100 amp BMBes the total current would be 100 amps.

Voltage is nothing more that the electrical potential. Current is the actual charge moving.

Let us use a gravitational energy analogy. potential is the size of the hill, the current would be the number of rocks rolling down the hill.
putting two batteries in series would be like doubling the height of the hill, but rolling down the same number of rocks

if you put batteries in parallel, it is the opposite. the hill is the same size but you double the number of rocks.

putting two 12 volt batteries in parallel, let us says two 12 v batterys with 100 amp BMS one would get 12v x 200amps max or 2400 watts.

both configuration whether in series or parallel would put out the same max energy.
 
Motormouth said:
I want to experiment with making a small starter system that I can use as an UPS
My neighborhood has had at least 5 multi-day outages in the last 20 years, which is very inconvenient.
I have a whole house back up generator, with a manual transfer switch, it works well but as you know you temporarily lose power with this configuration

Right now I have a couple APC UPS which work ok, but have very limited capacity.
For this build, solar is a nice to have but not the primary use of the system, rather I want to be able to backup all my network equipment, ie routers, switch, nas, maybe a refrigerator or two.

So after looking some of Will's and Ian's (Watts 247) videos ended up ordering a MPP Solar 2724LV-MR, it has AVR capability

I want make something similar to what is on this youtube video:

So two questions,

Question 1) one for the AC input to the 2724LW-MR the manual suggests a 40 amp direct wiring. I would like use a 30 amp plug (ie a TT30 or nema L5-30) so that I can hook it up to my 3500 W inverter generator or use a 30 amp outlet let that I would install in the house
Do I need to go up to a 50 amp plug or will the 30 amp be sufficient (ie the all in one is 2700 watts or 2700Watts/120v = 22.5 amps)? or is 40 amp wiring that critical for things like surge?
Both Will and Ian wired theirs up with 15 amp lines on their demo videos.

Question 2) Batteries, the manual suggested at leat 100ah batteries (ie I was thinking two 12.8 V 100ah batteries, but these usually have 100 amp BMS), will this be enough? If, the batteries only have 100 amp BMSes, that would only be 2400 Watts they could pull, and the unit is 2700 watts. Do I need to find batteries with at least 120 amp BMSes? or can I get away with the more common 100 amp BMS batteries out there. Larger capacity batteries usually have larger BMS, (but not always) and some times lower capacity batteries have small BMSes, again not always. What are your thoughts?

Eventually I will need to replace my roof, in about 3-5 years, and want to be ready to go big, ie SolArk 15K or 18K EG4/luxpower, or what ever else is out at that time and 20+ KWh batteries, etc. At that point I will use this little system in my little cabin.
Click to expand...
I have the 2724 MPP - I use it as my moble system.
PV - you can only attach 750W of solar to this intverter. ie not a lot. a separate SCC can be added for solar if you need it later.
Input AC - 30 Amp will feed it just fine. The amperage the unit will draw is programable, you could use 15A if that is what you have handy.
Batteries - 100 A is not sufficient if you plan to use the full capacity of this inverter.
2700W/24vDC 113Amps allowing additional 15% for peak you will want at least 135Amps. I built a DIY battery from 304Ah cells and Daly 150A BMS, and 150A 2P breaker. The MPP2724 can start a skillsaw or a shop vac if you put enough battery behind it.
I don't recommend two 12v batteries in series. Go 24v DC .

The 2724 can not be parallelled with a second unit. The MPP 3048 can be set up parallel, but costs a lot more.
 
Rednecktek said:
Nope, I was completely off. Please disregard, not enough coffee in me yet. ?
Click to expand...
No worries, ;)

Your comment about the BMS is very useful. Most of the batteries I could find in my price range were either 2 x 12V 100 ah batteries or 1 x 24v 100 ah battery, I could not find anything with more than a 100 amp BMS in this price range. I am not an expert on battery discharges but maybe the physical limit of the cells are being reached??? I don't know. Alas I only need to get 112.5 amps to max out the unit.

Going to a 200 ah battery to get a 150a or 200a max BMS gets really expensive for a little system. :(

Maybe I should get battery cells and bms and make my own batteries. As you said Daly makes some of the odd ball BMS including 120a ones
 
OffGridForGood said:
I have the 2724 MPP - I use it as my moble system.
PV - you can only attach 750W of solar to this intverter. ie not a lot. a separate SCC can be added for solar if you need it later.
Input AC - 30 Amp will feed it just fine. The amperage the unit will draw is programable, you could use 15A if that is what you have handy.
Batteries - 100 A is not sufficient if you plan to use the full capacity of this inverter.
2700W/24vDC 113Amps allowing additional 15% for peak you will want at least 135Amps. I built a DIY battery from 304Ah cells and Daly 150A BMS, and 150A 2P breaker. The MPP2724 can start a skillsaw or a shop vac if you put enough battery behind it.
I don't recommend two 12v batteries in series. Go 24v DC .

The 2724 can not be parallelled with a second unit. The MPP 3048 can be set up parallel, but costs a lot more.
Click to expand...
Thanks!! this is useful. I didn't think about the head room on the bms, good advice

I am a bit new to this, but the cells that you used, were they 3.2 volt ones? Where did you get them? the Daly did you get it on Amazon or is there a better place.

The reason I was thinking of two 12v batteries is they are generally cheaper than one 24 volt. I really like what you did building your own.

Originally I was thing about getting a LV6048 (the high frequency one) they have then for overstock both on Watts247 and Current Connected.
I like the idea of having either a 240V or 120v system and 6000 Watts would be nice, could run much of a house. But when we were getting into $1200++ for 5120 Wh of batteries and the LV6048 really needs 10K+ Wh to really get it running to it's full potential, wow I was not ready for that.

Wanted to start with something small I could learn from. like now.
I got the 2724 inexpensively over at mpp solar's store site (maximum solar_us).
 
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Motormouth said:
I am not an expert on battery discharges but maybe the physical limit of the cells are being reached??? I don't know. Alas I only need to get 112.5 amps to max out the unit.
Click to expand...
For 100Ah batteries it's pushing the 1c max rate the batteries are rated for. Going higher capacity (i.e. a 200Ah battery) usually has larger cells so your C rate of 1 is much higher.

It might be worth it to DIY a battery. An 8s battery is only complicated if you don't pay attention to the JK wiring diagram like I did. Avoid Daly, they're pretty bad in comparison to JBD or its clones.
 
Rednecktek said:
For 100Ah batteries it's pushing the 1c max rate the batteries are rated for. Going higher capacity (i.e. a 200Ah battery) usually has larger cells so your C rate of 1 is much higher.

It might be worth it to DIY a battery. An 8s battery is only complicated if you don't pay attention to the JK wiring diagram like I did. Avoid Daly, they're pretty bad in comparison to JBD or its clones.
Click to expand...
I used 304Ah cells to limit the discharge rate - always less than 0.5C, generally less than 0.3C
I prefer the JK over the Daly BMS's generally, however this DIY pack needed a 150A (or higher) 8S BMS, I only found Daly/JK in this capacity at the time I built the pack. The Daly has done it's job fine on this battery pack for a few years now, so I can't complain.
 
you can find cells from USA warehouses - many of the guys like 18650-battery-store in GA. they sell the EVE and Envision cells.
a search of the forum will show you some other suppliers for cells
you can find Daly or JK BMS on Amazon, Ebay or from Aliexpress.
 
I went with a 100ah minimal sized battery for this inverter as I intended on high amp low overall kwh use in its portable form on the hand truck.
With that being said, I have also been using this to power a shed when not in heavy use; low draw electronics, fridge, and intermittent computer use. currently using a small 440w array for testing this past year. The 440w of solar is more than keeping up with power requirements, but the 100ah battery is on the near edge to run what I'm running with 3 days of fog or bad weather.
I have a larger battery pack which will be left immobile in the shed and used next year to get through any extremes in weather.
If one doesn't want something as portable or is vehicle mounted, I highly recommend at least 5kwh battery for this inverter if used under a required constant low draw continuous load scenario. (electronics, freezer, refrigerator, etc.)

If one maxes out the solar 750w and can deal with the low 60v voc requirement and use a minimum 5kwh battery, this is a very ideal setup for endless power under multiple scenarios. Very versatile, reliable, and easy to use inverter.
 
@OffGridForGood
I checked out the 18650-battery-store, funny I have a bunch of 18650 cells for some other specialized equipment I own.
Looks like there prices are very good on LiFePO4 cells!!!

@BuffaloTrace
Good to know about the constrains of only going with a 100ah battery. BTW I love your solar hand truck
 
To support the top end peak - ie to start up demanding motors like skillsaws - The MPP 2724 will top out at 136A DC draw, actually a bit higher for a fraction of a second, so I wanted a 150A max battery output, at 0.5C so went with the 304Ah cells and 150A BMS (Daly in this case). An 8S battery pack is about 100lbs, so this was about the heaviest I wanted to go for a portable set up. Put Anderson plugs on the battery to Inverter connection and it will be easier to load in a car for camping trips. The Inverter already has MC-4 connectors for the PV inputs (I typically don't bother with PV while mobile, only when this set up is in the shop or the Greenhouse). This rig has been running lots of demanding loads around the homestead, and I can't complain about the Daly in this application because it works great. (I like the JK BMS for my 48v packs).
I have never needed to use it, but I always feel that having a small mobile battery/inverter set up will be a good back up to my main 48v system if anything 'bad' ever happens to the stationary power plant. Always good to have a back up, I also have a really small 12v more-portable rig on AGM cells, usually attached to my ATV.
 
I like the idea of 304Ah cells with the 150A BMS, for the 2724 will let you know what I end up doing.
This does seem to be about the weight limit one could go and still have it semi-mobile.
The weight is always going to be a problem unless someone figures a way out to make a higher energy density batteries (I was never that great at electro-chemistry). I know the issues with hydrocarbons, but the energy density is so high with fossil fuels (the biggest reason they were and still are used)

When I get house re-roofed in a couple years, would like to put at least 10kWh-20kWh hour 48 volt system in the house (with solar of-course).
Like you after that I want to keep this little system as a backup or in my big shed (that is really the sized of a small cabin.)
 
Motormouth said:
The weight is always going to be a problem
Click to expand...
you could build two packs using 150Ah cells, and make up a spliter cord, so you can disconnect and reconnect easily. The smaller cells are also about half the weight of the 304's so easier to move around if needed, ie if a cart doesn't always work - ie getting the rig into and out of a car or van for example.
 
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