diy solar

diy solar

4 new cells off the boat now what??

NEWYORKHILLBILLY

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May 12, 2020
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I been reading lots on the forum and watching wills videos. I am still little confused on balance and capacity testing .

I order 4 eve 280ah new cells for a 4s system. for RV
what steps do i take to balance and confirm capacity of these cell?
Do I top or bottom balance?.

here is the tools i ordered did i miss something or is this enough to get the job done?

10 amp bench power supply
batt go 8s meter
20amp/150w adjustable battery load tester. ( thats the fan unit will used in his videos that had a capacity meter)

my system
280AH 4s
Chinse 120amp BMS bluetooth
380watts solar
victron mppt
victron 712 battery monitor
 
Top balance.

Put the 4 cells in parallel, set bench power supply to 3.60 - 3.65v. Charge to zero on the amps. Done

Will's video was pretty straight forward.

 
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TThis is where I get confussed in this video he recommends bottom balancing for solar and not top balancing time 4.20 . so should i top or bottom balance the cells?


 
Ignore that video. When using solar just top balancing, charging with solar you'll be in the middle/ upper voltages than lower.

Use proper settings for the SCC and life should be long and happy.

Bottom balancing is more for EV were charging might be long in between so they want all of the juice from the cells and are at the lower/ bottom voltage more often than not.
 
Ignore that video. When using solar just top balancing, charging with solar you'll be in the middle/ upper voltages than lower.

Use proper settings for the SCC and life should be long and happy.

Bottom balancing is more for EV were charging might be long in between so they want all of the juice from the cells and are at the lower/ bottom voltage more often than not.
That is good to know. I should have everything i need ordered to do that. of course assuming my cell's arrive as advertized
 
Ignore that video. When using solar just top balancing, charging with solar you'll be in the middle/ upper voltages than lower.

Use proper settings for the SCC and life should be long and happy.

Bottom balancing is more for EV were charging might be long in between so they want all of the juice from the cells and are at the lower/ bottom voltage more often than not.
For me, I like to get the cells as close as possible at the bottom because when the sun is scarce, I'll likely be dipping right into available capacity and more often than not getting close to full discharge, so I need the cells to reach that lower voltage together so as:- 1, I'm using all available cell capacity
and 2, I'm not in danger of not noticing one cell getting dangerously low while the others are fine. Because I set my SCC to only charge to 90% or so, there is room for slightly different top voltages. If one cell gets low before the rest, that's a fair percentage of capacity lost due to 1 cell turning the system off.
As I run solar and have small charge/discharge currents, the cells don't drift out of balance. With the Ev world, massive currents are drawn, amplifying any difference in IR.
 
For me, I like to get the cells as close as possible at the bottom because when the sun is scarce, I'll likely be dipping right into available capacity and more often than not getting close to full discharge, so I need the cells to reach that lower voltage together so as:- 1, I'm using all available cell capacity
and 2, I'm not in danger of not noticing one cell getting dangerously low while the others are fine. Because I set my SCC to only charge to 90% or so, there is room for slightly different top voltages. If one cell gets low before the rest, that's a fair percentage of capacity lost due to 1 cell turning the system off.
As I run solar and have small charge/discharge currents, the cells don't drift out of balance. With the Ev world, massive currents are drawn, amplifying any difference in IR.
We all have choices for what poison works for us, having scarce sun has you using bottom balancing.

I'm a top balance user but sun is mostly plentiful.
I get near the bottom myself if after 3 days of poor solar with little to no solar charging. My longest is 40 days of PSOC during the winter season of bouncing between 25% ‐ 90% and still having loads of 175a to 200a being used at low SOC. The cells all stay relatively close (40-60mV).

Having protection in place at both ends of the spectrum is key though. ;)

It's good to have choices and know what work for the condition of use.
 
For me, I like to get the cells as close as possible at the bottom because when the sun is scarce, I'll likely be dipping right into available capacity and more often than not getting close to full discharge, so I need the cells to reach that lower voltage together so as:- 1, I'm using all available cell capacity
and 2, I'm not in danger of not noticing one cell getting dangerously low while the others are fine. Because I set my SCC to only charge to 90% or so, there is room for slightly different top voltages. If one cell gets low before the rest, that's a fair percentage of capacity lost due to 1 cell turning the system off.
As I run solar and have small charge/discharge currents, the cells don't drift out of balance. With the Ev world, massive currents are drawn, amplifying any difference in IR.
my system would be very similar to your. Now i know why i getting confused there seem to be two schools of thought on this.
 
my system would be very similar to your. Now i know why i getting confused there seem to be two schools of thought on this.
Will you have a generator to charge if you need it?

Just for reference, it helps to know what your average daily loads will be.

Winter is the shortest period for charging with solar so my sunset to sunrise average can be 35-45% (175-225ah), as long as the batteries are at 55-60% after dinner all should be fine for the next morning before the sun can start it's charging. Got to have power for the Mr Coffee 12 cup coffee and 5 minutes of microwave use for breakfast.

If I need to I run my 1 eu2000i generator for 1 hour and dump 100ah (20%) charge into the batteries for a hold over charge so sun can do its thing the next day. If it's going to be a poor solar day I'll let the generator run for 2 hours and that will dump 200ah (40%) in to the batteries.
 
You can just hook it up, your bms will balance but hopefully you never need to worry about it.

I'm not sure why people are spending so much time balancing manually, unless you are bored or something.

If you have no BMS then bottom balance. Or just get a bms.
 
You can just hook it up, your bms will balance but hopefully you never need to worry about it.

I'm not sure why people are spending so much time balancing manually, unless you are bored or something.

If you have no BMS then bottom balance. Or just get a bms.
I'm not sure people are lol, just good practice to get good balance with new cells/unknown soc as a starting point. Once that's achieved, bms does the rest.
 
Will you have a generator to charge if you need it?

Just for reference, it helps to know what your average daily loads will be.

Winter is the shortest period for charging with solar so my sunset to sunrise average can be 35-45% (175-225ah), as long as the batteries are at 55-60% after dinner all should be fine for the next morning before the sun can start it's charging. Got to have power for the Mr Coffee 12 cup coffee and 5 minutes of microwave use for breakfast.

If I need to I run my 1 eu2000i generator for 1 hour and dump 100ah (20%) charge into the batteries for a hold over charge so sun can do its thing the next day. If it's going to be a poor solar day I'll let the generator run for 2 hours and that will dump 200ah (40%) in to the batteries.

I will have a Honda 2000 with me, My plan is not to use it. My amp draw will be low no inverter. I planning for the worst case with would be late fall with cold temps. rv furnace and cpav machine would be my big draws.In the past i would have plenty of power except on cold night with little sune the day before that was with 224ah of lead acid . so i could only use 110 amp hours and that would drop when temps dropped. the New DIY battery will be 280ah
 
Ah, you're going to love your new batteries! Great thing is, is that worst comes to the worst, if you do have to top up with Honda power, the batteries just soak up the charge, no worrying about going all the way and topping off charge like with lead acid. My time on 800ah of agm I will not miss, especially looking after them in winter.
 
Ah, you're going to love your new batteries! Great thing is, is that worst comes to the worst, if you do have to top up with Honda power, the batteries just soak up the charge, no worrying about going all the way and topping off charge like with lead acid. My time on 800ah of agm I will not miss, especially looking after them in winter.
Yes that was a problem before the honda get me to 80% quick but the last 20% would take way longer than i was willing to wait. I had ordered my new trailer before I decided on The DIY battery. I ordered 2 190 watt panels on the roof , my trailer build will be done late July. with those panles and my new diy 280ah battery i should have plenty of power. I even thought of adding a inverter because i feel in summer i have so much extra power i could put to use.
 
Without a BMS, the bottom balance is important so that all cells receive the same depth of discharge and should share the load fairly equally. You won't have one cell working too hard and failing premature.
There is really no reason not to have a bms anymore. They are so cheap and easy to install, its just common sense to spend $50 to protect your $500 batteries.
 
so if i understand this , best to just top balance and use a bms
As I understand it, for most solar/camper/RV setups, that is the way to go.
When you get into the high discharge rates and potential low battery states of something like electric vehicles, then bottom balance becomes more important.
If all your cells are about the same age, and in the same condition, there won't be a lot of difference.
Safety should always come first,and the BMS is the safety net.
 
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