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diy solar

BMS needed?

When showing the loads, don’t use amps... amps are a confusing metric... use Watts...
20 amps at 12V is 240 watts... 20A at 120V is 2400Watts...
I see!! Okay well my initial calculation ended up being something ridiculous like 9600 watts per day. That was including using the electric heater 6-8 hours out of the day as well as the fridge. But at one time the biggest draw should be around 3000 running Watts.
 
The powered jack in the front hitch uses 12v, the motors for the slides uses the 12v, all the lights in the trailer uses 12v, the propane heater uses the 12v and the fridge uses the 12v. other than that the electric heater uses the 110v but it will also draw from the battery bank if I don't have shore hook up. So far the electric heater running non stop with the propane heater coming off and on as well as the 12v fridge has not tripped my 20 amp breaker from the garage outlet.
Ok, this shows some of the loads.
Let’s say 2000 watts max. So, you need an inverter capable of that, and a BMS that can handle the combined loads of your 12V loads, and the inverter load... 2000W at 12V is 167Amps... plus the 12V loads, likely another 30A... so, 190A... figure 25% oversized for comfort, and you need a 250A continuous BMS...

Now, if you arrange the cells in a 24V arrangement, the 2000W inverter drops to 84A, and the 12V is still 30A, so a 40A buck converter to power those loads, brings the BMS down to a 104A average, and you can work with a 150A BMS...

does that make sense?
 
I see!! Okay well my initial calculation ended up being something ridiculous like 9600 watts per day. That was including using the electric heater 6-8 hours out of the day as well as the fridge. But at one time the biggest draw should be around 3000 running Watts.
Here is another misunderstanding...
You won’t be using 9600Watts per day. You will be averaging 9600Watt-hours per day. A very big difference.

the electric heater uses say 1500Watts constant, but may only use 800, or over 36,000 Wh per day... it is a difference of usage versus demand.
 
The electric heater will be the killer .... it's really not practical to run that off your pack.
 
I see!! Okay well my initial calculation ended up being something ridiculous like 9600 watts per day. That was including using the electric heater 6-8 hours out of the day as well as the fridge. But at one time the biggest draw should be around 3000 running Watts.
Did you mean 9600 Watt-hours per day above?
Earlier you mentioned 3kWh per day this is probably your new number.

If you are drawing 3kW from batteries that is 234A before efficiency losses.
 
Did you mean 9600 Watt-hours per day above?
Earlier you mentioned 3kWh per day this is probably your new number.

If you are drawing 3kW from batteries that is 234A before efficiency losses.
I did mean 9600 watt hours per day, but when I take the electric heater out of the equation then it comes to about 3000 watt hours per day.
 
Here is another misunderstanding...
You won’t be using 9600Watts per day. You will be averaging 9600Watt-hours per day. A very big difference.

the electric heater uses say 1500Watts constant, but may only use 800, or over 36,000 Wh per day... it is a difference of usage versus demand.
oh man I am learning new stuff right now. maybe I did my math wrong.
 
Ok, this shows some of the loads.
Let’s say 2000 watts max. So, you need an inverter capable of that, and a BMS that can handle the combined loads of your 12V loads, and the inverter load... 2000W at 12V is 167Amps... plus the 12V loads, likely another 30A... so, 190A... figure 25% oversized for comfort, and you need a 250A continuous BMS...

Now, if you arrange the cells in a 24V arrangement, the 2000W inverter drops to 84A, and the 12V is still 30A, so a 40A buck converter to power those loads, brings the BMS down to a 104A average, and you can work with a 150A BMS...

does that make sense?
it kind of makes sense, but I am not sure I get having the 24v arrangement but still getting 12v from it. I also don't know how many BMS I would need for this, but I do see that I need a 150A BMS. BTW my inverter is a 3000 watt inverter
 
Are you totally sold on using the 100 AH cells? You could use the 280 or 272 AH cells which are popular and have a LOT less cells. This would make everything easier .... but you gotta make sure you have your usage numbers worked out as well as peak current needs.
For instance, the 1500 W heater 115 amps from a 12V battery by itself .... assuming a pack voltage of 13 V

I think you are getting bad advice from the guy selling the 100 AH cells.
 
Are you totally sold on using the 100 AH cells? You could use the 280 or 272 AH cells which are popular and have a LOT less cells. This would make everything easier .... but you gotta make sure you have your usage numbers worked out as well as peak current needs.
For instance, the 1500 W heater 115 amps from a 12V battery by itself .... assuming a pack voltage of 13 V

I think you are getting bad advice from the guy selling the 100 AH cells.
I watched a video from Will about the fortune 100 Ah cells and he had great things to say from it. I used his website link and bought those cells. I tried buying the other premade batteries Will had on his site but they were backordered and I won't have a home in 3 weeks and I could not wait 2 months from the time I ordered which was about a few weeks ago. It took about 6 months of order for my trailer to get here so I didn't know exactly what I could fit until it got here. excuses excuses I know, but the fact is I have the cells already and the panels are up on the roof installed already. So I gotta make this work.
 
For instance .... your 8 100 AH packs would be 800 AH (10.4 KW). If you did 3 280 AH packs instead, you would have 840 AH (10.92KW).

Edit.... AHHH .... didn't realize you already bought the batteries. The fortune cells are nice.
 
it kind of makes sense, but I am not sure I get having the 24v arrangement but still getting 12v from it. I also don't know how many BMS I would need for this, but I do see that I need a 150A BMS. BTW my inverter is a 3000 watt inverter
Ok, a 3000 watt inverter you ALREADY have. Is it a 12V or 24 v inverter? If you already have it, the cells must be arranged for 12V...
 
it kind of makes sense, but I am not sure I get having the 24v arrangement but still getting 12v from it. I also don't know how many BMS I would need for this, but I do see that I need a 150A BMS. BTW my inverter is a 3000 watt inverter
If you have continuous loads of 3kW then that is 234A. With a conservative inverter efficiency of 80% requires current draw of 293A from battery. You may want your BMS discharge current to exceed this by 20%.

Your total current requirements are 350A discharge and 150A charging. Might want to consider arranging some of cells into at least two parallel batteries otherwise the BMS may be pricey and hard to source in the limited time frame you have.
 
I watched a video from Will about the fortune 100 Ah cells and he had great things to say from it. I used his website link and bought those cells. I tried buying the other premade batteries Will had on his site but they were backordered and I won't have a home in 3 weeks and I could not wait 2 months from the time I ordered which was about a few weeks ago. It took about 6 months of order for my trailer to get here so I didn't know exactly what I could fit until it got here. excuses excuses I know, but the fact is I have the cells already and the panels are up on the roof installed already. So I gotta make this work.
Here is how I would approach this, for the simple fact you need a good sized inverter and your cells are 100Ah. I would go with 24v to reduce the amp draw. Not only does it help with wire size but the BMS's you use can be lower amp rating and give more headroom. I would also parallel cells first to double the Ah and require less BMS's. 2P8S packs gives you 24v per pack and gives you 2 24v batteries in parallel with 32 cells. A 3000w inverter would draw 125 amps on 24v plus you need to add some headroom. With 2 parallel battery packs, each BMS would only need to be rated at 70 amps, easily done with 2 24v Overkill 8s BMS's rated at 100 amps each. This also gives you plenty of headroom. One other advantage is if you have a BMS go down on one battery pack or a bad cell, you still have some capability with the remaining battery pack. As you will be living in it full time, this is the best solution. However you will overload the BMS if you run the inverter under full load in such circumstances so if this occurred you will still be able to operate many devices but would have to monitor load until you can get the other battery pack online.
 
Ok, a 3000 watt inverter you ALREADY have. Is it a 12V or 24 v inverter? If you already have it, the cells must be arranged for 12V...
Its a 12v inverter..... I wanted to go with a 24v system but I was told by the rep at electriccarparts.com that it is much easier to keep it 12v because all my stuff is 12v and I would lose efficiency by stepping down to 12v.
 
Here is how I would approach this, for the simple fact you need a good sized inverter and your cells are 100Ah. I would go with 24v to reduce the amp draw. Not only does it help with wire size but the BMS's you use can be lower amp rating and give more headroom. I would also parallel cells first to double the Ah and require less BMS's. 2P8S packs gives you 24v per pack and gives you 2 24v batteries in parallel with 32 cells. A 3000w inverter would draw 125 amps on 24v plus you need to add some headroom. With 2 parallel battery packs, each BMS would only need to be rated at 70 amps, easily done with 2 24v Overkill 8s BMS's rated at 100 amps each. This also gives you plenty of headroom. One other advantage is if you have a BMS go down on one battery pack or a bad cell, you still have some capability with the remaining battery pack. As you will be living in it full time, this is the best solution. However you will overload the BMS if you run the inverter under full load in such circumstances so if this occurred you will still be able to operate many devices but would have to monitor load until you can get the other battery pack online.
Thanks but I am trying to work with what I have and not go through returning things for the second time..... I should have not listened to the rep but he broke me down. no excuses but I have a weak spot for elders.....
 
If you have continuous loads of 3kW then that is 234A. With a conservative inverter efficiency of 80% requires current draw of 293A from battery. You may want your BMS discharge current to exceed this by 20%.

Your total current requirements are 350A discharge and 150A charging. Might want to consider arranging some of cells into at least two parallel batteries otherwise the BMS may be pricey and hard to source in the limited time frame you have.
I see so going by what you are saying does that mean I could get away with 4 BMS each one rated for 150A charging and 350A discharging? I was looking at going with 4 Overkill 120A BMS 8 gauge wires with 3/8 copper terminals on it. Would that work?
 
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Thanks but I am trying to work with what I have and not go through returning things for the second time..... I should have not listened to the rep but he broke me down. no excuses but I have a weak spot for elders.....
You're willing long term to put up with something less efficient and that causes headaches because you listened to someone that didn't have any idea what they were advising?

Running a 3000w inverter long term on 12v is just not economical and will most likely be short lived. The reason is heat. Truckers for a long time have been hooking up large inverters on 12v only to find longevity isn't there. The units fail due to the heat generated from the large amount of amps running on 12v. 24v allows the amps to be doubled. It is the simple solution to everything that presents a challenge in your system. Copper is not cheap, you're going to find that staying at 12v will be expensive when it comes to wiring plus you will have added expense with more BMS's needed.
 
Quality 12v inverters work just fine. So that's just bunk.

But I agree there is no reason to compromise your full time living because some fool trying to make a buck wants to take you for a ride.

One should only use 12V at those power levels if they have a specific reason to.
 
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Quality 12v inverters work just fine. So that's just bunk.

But I agree there is no reason to compromise your full time living because some fool trying to make a buck wants to take you for a ride.

One should only use 12V at those power levels of they have a specific reason to.
Reason is half of my trailer runs off of 12v. So I was agreeing with the guy that it didn't make sense that I was trying to go with 24v just to drop some of it back down to 12v. However I will be using 110v for the other half of the trailer so is it better to just use a step down converter for 24v to 12v or just keep it 12v?
 
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