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Old 02-18-2022, 11:44 AM   #1
Mini-Skoolie
 
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Protecting Batteries when pulling DC and Inverter-> AC

Hey,

In planning for our DC appliances within our electrical/solar build, we are learning that people will connect a DC panel straight to the battery bank.

When talking to an electrician about this, he was concerned that the batteries might get damaged because the DC panel doesn't have any tech/info stopping the appliances from over-draining the batteries. Our inverter that is connected to the 120V AC panel does have that technology, but it would never know how much the DC panel is pulling from the batteries at any given time.

Does anybody have a solution for this? I found some battery monitors on amazon that we could hook up and just check often when running our DC appliances to make sure the batteries don't drain too low. However we would love something to be built into the system so we wouldn't have to constantly worry and monitor the batteries.

Thanks!

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Old 02-18-2022, 12:31 PM   #2
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There are numerous ways to achieve your goal. Here's but one potential solution:

https://www.amazon.com/Victron-Energ...750032069&th=1
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Old 02-18-2022, 01:24 PM   #3
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Thanks so much!! That battery protector looks great
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Old 02-18-2022, 04:50 PM   #4
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If using lithium with a BMS wouldn't the BMS provide this function?
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Old 02-18-2022, 04:55 PM   #5
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Originally Posted by HamSkoolie View Post
If using lithium with a BMS wouldn't the BMS provide this function?
I hope so, I'm kinda counting on it in my bus
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Old 02-18-2022, 07:33 PM   #6
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Quote:
Originally Posted by HamSkoolie View Post
If using lithium with a BMS wouldn't the BMS provide this function?
Quote:
Originally Posted by Rwnielsen View Post
I hope so, I'm kinda counting on it in my bus
They typically do, but I'd rely on the BMS for this only as a last resort. Best to design the system such that the inverter proactively fails off first, DC appliances second by some means like a Victron Battery Protect. The BMS comes in only after that, in case the other safety mechanisms fail.
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Old 02-18-2022, 07:34 PM   #7
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Agreed.
Also, OP never said anything about lithium.
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Old 02-19-2022, 09:13 AM   #8
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Quote:
Originally Posted by HamSkoolie View Post
If using lithium with a BMS wouldn't the BMS provide this function?
Quote:
Originally Posted by kazetsukai View Post
They typically do, but I'd rely on the BMS for this only as a last resort. Best to design the system such that the inverter proactively fails off first, DC appliances second by some means like a Victron Battery Protect. The BMS comes in only after that, in case the other safety mechanisms fail.
I didn't even know what a BMS was until that post so that's great to know! Also yes, our batteries are lithium.

After doing some research, the battery website does say that if the BMS kicks in and the voltage shows 0V, we'd need a compatible lithium charger to reactivate the batteries. Not sure if our current system could act as one, or if we'd need to bring a designated charger with us which would *not* be ideal.
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Old 02-19-2022, 10:50 AM   #9
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my victron 700 series BMS has a dry contact closure that you could use to open a relay when the batteries reach a pre-set voltage.. or you can program it to use their built in SOC estimate.. im thinking most BMS have the ability to shut things off when the batteries are low.
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Old 02-23-2022, 03:11 PM   #10
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Quote:
Originally Posted by csulli View Post
Hey,

In planning for our DC appliances within our electrical/solar build, we are learning that people will connect a DC panel straight to the battery bank.

When talking to an electrician about this, he was concerned that the batteries might get damaged because the DC panel doesn't have any tech/info stopping the appliances from over-draining the batteries. Our inverter that is connected to the 120V AC panel does have that technology, but it would never know how much the DC panel is pulling from the batteries at any given time.

Does anybody have a solution for this? I found some battery monitors on amazon that we could hook up and just check often when running our DC appliances to make sure the batteries don't drain too low. However we would love something to be built into the system so we wouldn't have to constantly worry and monitor the batteries.

Thanks!
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Old 02-23-2022, 07:41 PM   #11
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Quote:
Originally Posted by csulli View Post
Hey,

In planning for our DC appliances within our electrical/solar build, we are learning that people will connect a DC panel straight to the battery bank.

When talking to an electrician about this, he was concerned that the batteries might get damaged because the DC panel doesn't have any tech/info stopping the appliances from over-draining the batteries. Our inverter that is connected to the 120V AC panel does have that technology, but it would never know how much the DC panel is pulling from the batteries at any given time.

Does anybody have a solution for this? I found some battery monitors on amazon that we could hook up and just check often when running our DC appliances to make sure the batteries don't drain too low. However we would love something to be built into the system so we wouldn't have to constantly worry and monitor the batteries.

Thanks!
A BMS, either built in to the battery or added before any loads (with one or two rare exceptions), will provide the safety switch if properly configured.

You should (in my opinion) incorporate a Smart Shunt (like Victron SmartShunt) so you can monitor battery usage and state of charge using an app on your smartphone. Maybe that's what you were referring to. That app will also give you a good idea of your charge/discharge cycle and actual capacity of solar panels under various conditions.
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Old 02-23-2022, 08:00 PM   #12
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is the Smartshunt part of my 702 victron? I installed a shunt as part of it..

I love the BMS but the % SOC estimator seems pretty off.. if I go with the SOC stabding voltage numbers from my battery manufacturer and assume the Victron is accurate in how many Amp hours im drawing down my batteries.. the SOC % on the BMS says 0% while estimating the SOC by way of the battery manufacturer chart has me still at about 25-30%.. granted I know you arent supposed to run AGM batteries down.. I was doing some experimenting.. maybe I just beed to tweak the BMS settings a bit
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Old 02-23-2022, 08:03 PM   #13
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Originally Posted by cadillackid View Post
maybe I just need to tweak the BMS settings a bit
I went with a Renogy shunt and had to set the capacity for the bank. Its more or less accurate within 10% or so, but reaches "100%" SOC probably 15% early. I think the issue there is charge efficiency, or something.
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Old 02-24-2022, 02:08 PM   #14
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My Renogy Solar Charge Controller under-reports voltage by .3 VDC consistently. The Victon SmartShunt never matches the charge controller State of Charge value-ever. There's an incredible amount of improvement needed in all of these systems.

Still, having that SmartShunt show me amps input/output and the charge controller show the power generated gave me enough information to tune the settings so I stick between 20 and 80 percent charge.
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Old 02-24-2022, 05:42 PM   #15
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Originally Posted by Rucker View Post
My Renogy Solar Charge Controller under-reports voltage by .3 VDC consistently. The Victon SmartShunt never matches the charge controller State of Charge value-ever. There's an incredible amount of improvement needed in all of these systems.

Still, having that SmartShunt show me amps input/output and the charge controller show the power generated gave me enough information to tune the settings so I stick between 20 and 80 percent charge.



see i thought they would adapt.. since you set the floor voltage of the batteries and the full voltage.. and the total AH capacity.. (im going on the label of the battery and assuming nearly new batteries would have full capacity).. but it seems they just count AH and thats it.. I have the victron 25 amp charger programmed with the same parameters.. i thought the idea of the victron smart devices is they talked to each other... but apparently not.. I plug the charger into shore power when the bus is at the "barn" and so it keeps the house batteries full (it will keep the starters full if I force the isolator on also since the yare the same type batteries).. but I dont generally have those connected as it isnt needed..



I could see the SOC indicator being off if theres always a load on the batteries.. but it doesnt even alter its value when the batteries have no load and will set at their voltage.. for what i paid for the victron 702 I guess i expected more out of it..
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Old 02-24-2022, 09:17 PM   #16
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The way I 'tuned' the settings on the charge controller was to hypothesize the upper voltage of my 208 amp hour LiFePo when 80% charged (13.3v based on the voltage at which I'd consumed 20% of the battery capacity), burned the charge down to 20% and used that as the boost voltage setting.

I forgot to rant about the Renogy parameters, those various 'boost', 'return', 'float' settings that are completely undocumented. Frustrating because I know I'm not fully understanding how the darn thing works.
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Old 04-09-2022, 04:39 PM   #17
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Thank you for all of the helpful input and info!

I went with the Victron Battery Protect. Quick side question - in placing it into my system, I also have a Terminal Fuse and manual on/off switch coming off the + side of my battery bank. In all the instruction videos they show the fuse in between the battery protect and the battery bank. Where would you guys suggest putting the manual on/off? Does it matter/ change anything depending on what side of the battery protect it is on? Maybe a silly question... it's just so specific I can't find an answer by just googling.
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Old 04-10-2022, 12:11 AM   #18
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Thank you for all of the helpful input and info!

I went with the Victron Battery Protect. Quick side question - in placing it into my system, I also have a Terminal Fuse and manual on/off switch coming off the + side of my battery bank. In all the instruction videos they show the fuse in between the battery protect and the battery bank. Where would you guys suggest putting the manual on/off? Does it matter/ change anything depending on what side of the battery protect it is on? Maybe a silly question... it's just so specific I can't find an answer by just googling.
The directions on their website show a manual disconnect on the negative battery side.
https://www.victronenergy.com/batter...attery-protect
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Old 04-10-2022, 09:00 AM   #19
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The directions on their website show a manual disconnect on the negative battery side.
https://www.victronenergy.com/batter...attery-protect

Hey,

Not sure where that is on the website, I see a remote on/off for the BP itself, but not a diagram/description of having a manual on/off for the whole battery circuit. Is there any way you could send that picture or quote directly?

The general consensus on most RV and marine online forums is that the battery disconnect can (and should) go on the positive end, so that disconnecting the positive side will keep the ground side negative. There are a lot of people talking about it, and both are done in different situations but I agree with most that it is safe and fine having it on the positive side for the system I am creating.

I'm sorry to reiterate, but if I was to put it on the positive end, would it matter if the manual on/off is placed before or after the BP?

Thanks
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Old 04-10-2022, 03:22 PM   #20
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Hey,

Not sure where that is on the website, I see a remote on/off for the BP itself, but not a diagram/description of having a manual on/off for the whole battery circuit. Is there any way you could send that picture or quote directly?

The general consensus on most RV and marine online forums is that the battery disconnect can (and should) go on the positive end, so that disconnecting the positive side will keep the ground side negative. There are a lot of people talking about it, and both are done in different situations but I agree with most that it is safe and fine having it on the positive side for the system I am creating.

I'm sorry to reiterate, but if I was to put it on the positive end, would it matter if the manual on/off is placed before or after the BP?

Thanks
On that page, roll down until you see the word Downloads. Select Manuals, and you will see a couple of PDF downloads labelled BatteryProtect 48V-100A and BatteryProtect 65A/100A/220A. Click on the one you have, and it will bring up information. At the bottom is a block diagram showing where the stuff is installed. The black wire will be the ground, and I'm assuming that the rather large M in a circle is the manual disconnect. Power goes from positive to the item being run (the load) to negative, and this shows the rather large M between the load and the negative terminal side of the battery string.
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