DcDc low voltage cut off solution?

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LeoKa

LeoKa

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Joined
Apr 15, 2017
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USA
Vessel Name
Ironsides
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54' steel custom
I have a Renogy DCDC 12V 60A device put between my two separate lithium banks (680Wh + 400Wh). It works fine, but the other day, the source bank was cut off due to low voltage (each lithium battery has its own BMS by factory). This bank is charged by solar panels, so at night, it can be used up completely. Everything came back fine, once the panels started to charge again.
Is there a way to disconnect the DCDC device from the source battery bank at certain voltage? How is this setup?
The installation manual of the DCDC does not address this scenario, because it assumes that the charge will come when the ignition wire is active. My setup has this wire always connected and my alternator is not involved in this configuration. I am just supplying the house battery bank from the solar battery bank. Again, it works very well, but I would not mind to have some kind of protection on the solar battery bank, so it will not go ' empty '.
 
To be sure I understand. Solar charges a solar battery bank and that charges the house bank via a DC2DC. You want to turn off the DC2DC when the solar is not charging. You did not say solar and house banks are same or different chemistry. So I will assume different and the reason to use the DC2DC.

Perhaps add a battery isolator, or a device that is one way. Run the solar panel wire into it and then out to the solar bank. Run a trigger wire from the solar panel side of isolator to the DC2DC trigger on/off.
 
SteveK said:
To be sure I understand. Solar charges a solar battery bank and that charges the house bank via a DC2DC. You want to turn off the DC2DC when the solar is not charging. You did not say solar and house banks are same or different chemistry. So I will assume different and the reason to use the DC2DC.

Perhaps add a battery isolator, or a device that is one way. Run the solar panel wire into it and then out to the solar bank. Run a trigger wire from the solar panel side of isolator to the DC2DC trigger on/off.
Click to expand...
Well, no. I do not want to isolate the solar battery bank.
I want the dc2dc charger stop drawing from it, when the voltage of the solar battery bank is too low.
Both battery banks are lithiums. The reason I need the dc2dc charger be involved, because the battery manufacturers (two different companies) told me that their batteries are not compatible with each other. I have no clue why, because they did not explain it to me. I was told, if I group them together, the warranty will be void.
The solar battery bank has 4 batteries to a busbar and my six solar panels have six solar chargers (Victrons). All works fine and this battery bank also feeds the 12V load to the boat.
The house battery bank is one large lithium battery and supplies the house with 110V through an inverter. Works very well, but when I am off the shore-power, it can run out of juice.
So, I connected these two banks with the dc2dc charger and they are all happy. Except, when there is not enough sun, or the AC side uses too much, the solar bank can deplete to the point where the BMS shuts each battery down. Not a problem, just leaves the house without 12V source, until the sun comes up.
 
I know next to nothing about your Renogy 12V 60 A DC2DC device but I potentially see at least 2 methods to solve this issue that I thought you had solved back in Feb. of 24 by setting lower voltage limits on the DC2DC. I guess not.

You need to determine if you want to turn the Renogy off by way of it's D+ signal wire or if you want to simply open the Renogy's connection to the solar battery bank.

If the former is good for you then this should work.

czh-labs.com

Chunzehui Low Voltage Disconnect Module LVD, 12V 10A, Protect/Prolong Battery Life.

Chunzehui Low Voltage Disconnect Module LVD, 12V 10A, Protect/Prolong Battery Life.
czh-labs.com czh-labs.com

If you would rather do the latter, maybe this.

czh-labs.com

10-30V 80Amp Low Voltage Disconnect LVD Module, for 12V 18V 24V Battery

10 to 30V 80Amp Low Voltage Disconnect LVD Module, for 12V 18V 24V Battery
czh-labs.com czh-labs.com

Yeah, both are from C_i_a, and likely made by a company that will change its name twice during the time it takes to ship the goods to you (about 2 weeks) but isn't that the norm these days?

Either method has its issues and if either of these Low Voltage Disconnects continue to work, they will do what you want, I just wish Google would have returned a part made by Siemens, Schneider, Eaton or some other well known entity. Maybe they are out there. Give your browser a try for LVD's. If you are stuck with either of the cheap units, buy a pair, one for stock on hand.

Just like the 80 Amp disconnect above, if you splurged and spent another $7.20 over the cost of the 10 Amp one that I linked, you could get a 30 Amp unit with settable voltage values (if they work for you) for disconnect and connect.

Here is their full product line for you to mull over.

Low Voltage Disconnect Low Voltage Cutoff

Low Voltage Disconnect Module, Low Voltage Cut-off Switch. Suitable for 12V 24V 36V 48V Batteries. Rated Current 10 / 30 / 80 Amps.
czh-labs.com czh-labs.com

Unless you have space in a box, stay with the packaged units.
 
luna said:
Here is their full product line for you to mull over.
Click to expand...


This is exactly what I was looking for. Since my dc2dc is rated 60A, I will go with this one:

czh-labs.com

10-30V 80Amp Low Voltage Disconnect LVD Module, for 12V 18V 24V Battery

10 to 30V 80Amp Low Voltage Disconnect LVD Module, for 12V 18V 24V Battery
czh-labs.com czh-labs.com

Yes, it is correct about the Renogy device. The pins do not do sh..t it seems. I tried different settings, but it behaves the same way no matter what. It works as a strait device and no adjustments. At least on lithium settings.

Thanks for the suggestion!
 
The issue with the disconnection of the high current approach is that opening an energized set of DC contacts can be quite a violent event. It's hard on the contacts which are likely not the best or even average to begin with. You can't take the unit back, can you!
Plus, even though we all try, we cannot guarantee that the load at the time of the disconnect, which occurs at a specific voltage and is not generally under your control, is not above 80 Amps if other things are powered by the solar charged battery.
With both of these things happening, you might need that 2nd unit that you bought quicker than you thought.

If it was me and I could not find a unit made from some western based company, I'd turn the power off using the D+ wire by using the 12 V 30 Amp unit so I had some ability to select the voltage.

This message will self destruct in 5 seconds, good luck Jim. You too Laszlo!
 
luna said:
If it was me and I could not find a unit made from some western based company, I'd turn the power off using the D+ wire by using the 12 V 30 Amp unit so I had some ability to select the voltage.
Click to expand...
If I understand your message correctly, you have no confidence on the devices you have recommended? Be it as it may, if I need to manually disconnect the D+ wire, I might as well just leave the thing alone and it will come back alive the next day. So why bother?
Having an auto disconnect solution would be a convenience, but not crucial.
I will keep searching.
 
SteveK said:
Perhaps add a battery isolator, or a device that is one way. Run the solar panel wire into it and then out to the solar bank. Run a trigger wire from the solar panel side of isolator to the DC2DC trigger on/off.
Click to expand...
Maybe I did not word the above correctly.
The battery isolator would prevent the source LFP bank from powering the DC2DC D+.
The solar panel would still charge the source bank thru the isolator, which would still charge the 2nd bank via DC2DC.
Taking a wire directly from the solar feed before the isolator to the D+ allows the solar panels to turn the DC2DC on/off.
Without the isolator the wire to D+ would take power from the source bank and keep the DC2DC "ON" after the sun goes down.
 
SteveK said:
Maybe I did not word the above correctly.
The battery isolator would prevent the source LFP bank from powering the DC2DC D+.
The solar panel would still charge the source bank thru the isolator, which would still charge the 2nd bank via DC2DC.
Taking a wire directly from the solar feed before the isolator to the D+ allows the solar panels to turn the DC2DC on/off.
Without the isolator the wire to D+ would take power from the source bank and keep the DC2DC "ON" after the sun goes down.
Click to expand...
I had to read it 3 times, but I think I get now. This might just work fine.
What battery isolator do you recommend?
 
How about this one:

www.victronenergy.com

BatteryProtect - Victron Energy

The BatteryProtect prevents the battery from being damaged. It disconnects the battery from non-essential loads before the battery is fully discharged.
www.victronenergy.com www.victronenergy.com
 
LeoKa said:
How about this one:

www.victronenergy.com

BatteryProtect - Victron Energy

The BatteryProtect prevents the battery from being damaged. It disconnects the battery from non-essential loads before the battery is fully discharged.
www.victronenergy.com www.victronenergy.com
Click to expand...
Well, that protects from total discharge which continues to allow source bank to charge 2nd bank. I thought the plan was to prevent source bank from topping up the 2nd bank by turning off the DC2DC.
 
LeoKa said:
If I understand your message correctly, you have no confidence on the devices you have recommended? Be it as it may, if I need to manually disconnect the D+ wire, I might as well just leave the thing alone and it will come back alive the next day. So why bother?
Having an auto disconnect solution would be a convenience, but not crucial.
I will keep searching.
Click to expand...

I don't think if one used the words "should work, maybe this, for you to mull over and buy a pair" it could be considered a recommendation. Maybe I'm wrong.

I would not chose the method you did (opening the high current circuit) because that is hard on contacts.

Opening the D+ circuit which likely has about 60 Milliamps on it is electronically really easy and either of the other 2 units I noted would do it automatically just fine I suspect. No manual switch is required. The reason to buy 2 of them is that for less than $20 in costs it's simply easier on the brain to have an on site spare. I also feel it almost guarantees that the one put in service will never fail!

Part of the purpose of my original post was to get you engaged in the search for and thought process in, selecting a device. I see that may have worked.

The Victron Battery Protect module uses MOSFETS instead of contacts so the arching issue is non existent. I suspect the originally offered 80 Amp unit could as well use MOSFETS, I just don't know as little info is available.
The problem with the Victron unit is the cautions noted in sentence 3.1.5 on Pg. 3 in the manual and the sketch on Pg.4.
I suspect that your DC2DC may have capacitors that will cause the short circuit protection into action or it may simply allow some small amount of reverse current that could kill the Victron.

Victron, as I do think the fix is to turn the thing off using the control (D+) circuit, which only needs a much smaller and cheaper switch.
 
SteveK said:
Well, that protects from total discharge which continues to allow source bank to charge 2nd bank. I thought the plan was to prevent source bank from topping up the 2nd bank by turning off the DC2DC.
Click to expand...
Correct. If I put the dc2dc activation wire D+ before this device and the panels are off (Victron MTTP shuts them off, if there is no amps coming down), the activation will not occur and nothing will flow to the target battery bank. So, the source bank will continue to feed the house with 12V, but this is very low load and it can easily handle it overnight.
This Victron can be set to a certain voltage to disengage. If I am correct, the solar battery bank will not discharge by feeding the house bank continuously, since the dc2dc charger is not active.
 
luna said:
I suspect that your DC2DC may have capacitors that will cause the short circuit protection into action or it may simply allow some small amount of reverse current that could kill the Victron.

Victron, as I do think the fix is to turn the thing off using the control (D+) circuit, which only needs a much smaller and cheaper switch.
Click to expand...
The dc2dc has some protections installed (over voltage, over temp, reverse polarity), but not much info is in the manual.


Understand that the cheaper solution is just as good enough, however, I like the BT connectivity on the Victron. It can give nice monitoring option for fine tuning. Who knows, the Victron MPPTs would like it, too. It is about $110 online.

 
Thats great that you like the Victron unit.
My understanding is that you simply want to turn your DC2DC off and that act alone will isolate the solar battery from the house battery, saving the solar battery in times of darkness.

If so just be careful to wire the Victron unit correctly.
 
Sorry guys for the late reply, but I was away doing a haul out and bottom paint.
Now I have read your replies more carefully and I think I misunderstood your recommendations.
I was keep thinking about high power disconnect solution, when the easier solution is just focusing on the D+ wire disconnect instead. Now I get it. If the D+ is disconnected, Renogy is off and no charge is transferred. No need for robust cabling and connections. No need for Victron BT.
I will browse again your suggestions and order something simple. Maybe double it, as Luna recommended.
Yeah, I am getting old.....
 
How low should I set the voltage disconnect for lithiums in your opinion?
 
If you are asking me, first you need to realize that I'm still stuck in the lead world and have not studied what are the needs of LiFePO4 batteries.
I would go with whatever the Battery Manufacturer indicates is a good low voltage disconnect set point to achieve battery longevity and then if I had excess capacity, I might increase the voltage set point by 0.1 volts, in order to disconnect earlier.
 
I am getting in the late. But I don't know why the two battery manufacturers say that they can't be used together. AS long as the charger is properly set up. In other word, if one has a max charge voltage of 14.3 and the other 14.0. Set the charger to 14.0V.

Maybe I am wrong, just trying to use some common seance.
 
Iggy said:
I am getting in the late. But I don't know why the two battery manufacturers say that they can't be used together. AS long as the charger is properly set up. In other word, if one has a max charge voltage of 14.3 and the other 14.0. Set the charger to 14.0V.

Maybe I am wrong, just trying to use some common seance.
Click to expand...
You can, but you will loose the warranty.
One company claims that the inverter/charger is not pure sine. The inverter company claims it is pure sine. Regardless, they both told me not to combine them, or I will not have warranty. I did not bother to keep asking questions, as the tech support is almost useless.
It is also possible that these two companies have some type of internal dispute.
My solution was to separate the AC and DC loads and use lithium bank for each purpose. The setup is working and I also have redundancy this way. Solar charging for DC bank. Shorepower/generator for the AC bank. All is good.
 
Something does not make sense to me. Kilovalt and Magnum had no problems in helping me setup my lifeP04 batteries with my charger/Inverter. Now in my 4th year, all good.
 
These days tech support should just say "support" as the word tech is overused to mean a too broad range of meanings. In most cases they are call center employees that following a computer screen display of what to say to you. Some places do not even hide it anymore and let an Ai bot answer you directly.
 
Iggy said:
Something does not make sense to me. Kilovalt and Magnum had no problems in helping me setup my lifeP04 batteries with my charger/Inverter. Now in my 4th year, all good.
Click to expand...
Good for you. I am settled already on this issue. After spending many thousands of dollars, I will not venture for another configuration. If something breaks, I will choose a different manufacturer.
 
SteveK said:
Some places do not even hide it anymore and let an Ai bot answer you directly.
Click to expand...
Bingo! First I did not believe it, but after several issues and the received replies, I had to realize that Ai dudes are answering back to me. Most of the answers are confusing, on a different subject, or just lack of understanding. If I complained enough with a loud mouth, I would get a human answer, but it was very rare. I have never spoken to a human. Only messaging.
 
LeoKa said:
Bingo! First I did not believe it, but after several issues and the received replies, I had to realize that Ai dudes are answering back to me. Most of the answers are confusing, on a different subject, or just lack of understanding. If I complained enough with a loud mouth, I would get a human answer, but it was very rare. I have never spoken to a human. Only messaging.
Click to expand...

What a sad state of affairs!
One has to wonder, is it that expensive/difficult to hire a real person with knowledge?
How did we get here?
 
LeoKa said:
Good for you. I am settled already on this issue. After spending many thousands of dollars, I will not venture for another configuration. If something breaks, I will choose a different manufacturer.
Click to expand...

I totally understand. You must do whats right for you.

I am just trying to understand from a tech point of view.
 
luna said:
What a sad state of affairs!
One has to wonder, is it that expensive/difficult to hire a real person with knowledge?
How did we get here?
Click to expand...
Yes, it’s very hard to find good technical people now. We’re all aging out, and there’s a big vacuum behind us. I’ve been looking for years to find an apprentice that might take over for me some day, but it’s not looking like that will happen as I’m running out of years to teach my craft…
 
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