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Old 04-07-2020, 08:55 PM   #71
Airtime
 
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Default Re: Airtime's electrical schematic for review please

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You can get these batteries for less than half the cost.

https://www.aliexpress.com/item/4000...2597324.pic_20

Check the inpedance: 0.2 - 0.3 mohm. That's 1.2 mohm for 12V. Of course the cell connections will increase total resistance, but no where near the 10 mohm seen on a typical self contained Li battery.
Ok you got me curious. Any thoughts on aluminum shell vs plastic? What I've read so far is plastic is supposed to be more robust, aluminum longer life but no actual data (??). The aluminum shells are even more compact, 2.1" thick cells vs 2.8" for 100-200Ah cells.

Here are some new 2020 Grade A CALB 180Ah aluminum shell cells, 4x for $632, with certs.
https://www.aliexpress.com/item/4000...e-ee69d7835cd8
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Old 04-07-2020, 09:27 PM   #72
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Default Re: Airtime's electrical schematic for review please

Case material isn't particularly important for this application. The MFGs have made significant strides in improving the materials and construction of the cells. CALB is more conservative, and still uses a lower density design. The newer blue aluminum prismatics are significantly smaller, but tend to cost slightly more per AH. CALB has a long history, which may have value for some buyers.

Aluminum is less flammable in a fire, but there is plenty of flammable electrolyte regardless. If you plan to have active heating of the cells, the aluminum case may offer better thermal conduction, and thus more even temperatures.
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Old Yesterday, 05:57 PM   #73
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Default Re: Airtime's electrical schematic for review please

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The biggest issue is overvoltage disconnect. That's encountered almost at a daily basis. I have 3 charging sources: 130W solar, 55A Iota converter and 40A Renogy dc/dc. All sources are handled individually.
Why is overvoltage tripped so often? Don't the charging sources have charging profiles that terminate more gracefully than that?

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It's important to disconnect solar at the panels. Just disconnecting at the output of the charge controller with panel power sill active is not advisable.
Why is that? I know that the solar panel connectors should not be disconnected under load due to arcing at the connector contacts. But why would a relay need to be on the input side of the solar charging controller rather than the output? Maybe to depower the charge controller to eliminate any quiescent current?

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My system is still a work in progress. I haven't completed any undervoltage disconnects yet.
Wouldn't the same disconnect relays work for undervoltage as well as overvoltage? Doesn't the BMS handle that via software?
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Old Yesterday, 06:02 PM   #74
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Default Re: Airtime's electrical schematic for review please

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Case material isn't particularly important for this application. The MFGs have made significant strides in improving the materials and construction of the cells. CALB is more conservative, and still uses a lower density design. The newer blue aluminum prismatics are significantly smaller, but tend to cost slightly more per AH. CALB has a long history, which may have value for some buyers.

Aluminum is less flammable in a fire, but there is plenty of flammable electrolyte regardless. If you plan to have active heating of the cells, the aluminum case may offer better thermal conduction, and thus more even temperatures.
Actually, the CALB aluminum shell cells I linked to above are significantly less that the CALB plastic shell. $632 for 4x 180Ah aluminum vs. $990 for 4x 200Ah plastic. Plus they are smaller, at 2.1" thick instead of 2.8"

So it doesn't sound like there is any downside for aluminum over plastic--still CALB brand, new grade A, but smaller and lower cost.
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Old Yesterday, 07:27 PM   #75
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Default Re: Airtime's electrical schematic for review please

I would be curious if the CALB AL/plastic cells have the same cycle rating? Its know that CALB under rates the cells in certain types to provide headroom for lots of cycles and still make the target capacity.
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Old Yesterday, 08:09 PM   #76
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Default Re: Airtime's electrical schematic for review please

1. What do you mean by "terminating charging more gracefully"? I see nothing wrong with the charging source set to 14V and the cell termination voltage at 3.45V (battery equivalent to 13.8V). Overvoltage trips often (than undervoltage) because the battery is usually a lot closer to 90% SOC than 20%. With a 40A dc/dc, overvoltage usually trips within the first hour of driving.

Are you saying the charging source should only be terminated when charging current is reduced to a trickle charge? That's what you'll get when charging voltage is set to 13.8V and cell overvoltage to 3.45V.

2. It's a requirement of many charge controllers to remove panel power in order to deactivate solar. Usually install instructions state to connect battery first before connecting panels to charge controller.

3. No, undervoltage disconnect relay will not work as an overvoltage disconnect. The undervoltage relay is located in a different location. In addition, you still want to charge the battery in a undervoltage condition and vice versa. The BMS provides two disconnect signals, one for undervoltage and the other for overvoltage.

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Originally Posted by Airtime View Post
1. Why is overvoltage tripped so often? Don't the charging sources have charging profiles that terminate more gracefully than that?


2. Why is that? I know that the solar panel connectors should not be disconnected under load due to arcing at the connector contacts. But why would a relay need to be on the input side of the solar charging controller rather than the output? Maybe to depower the charge controller to eliminate any quiescent current?


3. Wouldn't the same disconnect relays work for undervoltage as well as overvoltage? Doesn't the BMS handle that via software?
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Old Today, 02:10 AM   #77
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Default Re: Airtime's electrical schematic for review please

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1. What do you mean by "terminating charging more gracefully"? I see nothing wrong with the charging source set to 14V and the cell termination voltage at 3.45V (battery equivalent to 13.8V). Overvoltage trips often (than undervoltage) because the battery is usually a lot closer to 90% SOC than 20%. With a 40A dc/dc, overvoltage usually trips within the first hour of driving.

Are you saying the charging source should only be terminated when charging current is reduced to a trickle charge? That's what you'll get when charging voltage is set to 13.8V and cell overvoltage to 3.45V.
Maybe I'm misunderstanding you. My assumption was:
1) The charge profile settings in the charge controllers determine when charging stops based on parameters you set. I.e. voltage for charging and for termination current, etc. No relays or disconnects involved in normal operation. That's what I meant by "graceful"... the normal settings of a charge profile keeping the SOC of the battery bank in desired range.
2) My interpretation of "overvoltage" or "undervoltage" was more as a protection mechanism, in case for some reason the charge controller didn't stop charging--a protection relay that would disconnect the charging source to avoid over charging and overvoltage damage.

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2. It's a requirement of many charge controllers to remove panel power in order to deactivate solar. Usually install instructions state to connect battery first before connecting panels to charge controller.
OK good to know, I need to read my manual more closely.

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Originally Posted by calbiker View Post
3. No, undervoltage disconnect relay will not work as an overvoltage disconnect. The undervoltage relay is located in a different location. In addition, you still want to charge the battery in a undervoltage condition and vice versa. The BMS provides two disconnect signals, one for undervoltage and the other for overvoltage.
Again I may have misunderstood. I was again thinking of the charge controller handling this in normal operation, no relays involved. And then a load disconnect relay as a protection to prevent draining the battery in case something goes wrong.
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Old Today, 02:13 AM   #78
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Default Re: Airtime's electrical schematic for review please

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I would be curious if the CALB AL/plastic cells have the same cycle rating? Its know that CALB under rates the cells in certain types to provide headroom for lots of cycles and still make the target capacity.
Both are the same: Cycle life (80%DOD):4000 cycles
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