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Schematic for a 48VDC Battery Low Volt Disconnect

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Hello,
I've been browsing around trying to fine a schematic for a 48VDC low volt disconnect. So far I've only turned up LVD's for 12 & 24v schematic.

It would be super if the dropout voltage was adjustable with a pot between 40~50vdc.

From the circuits I've seen they look like pretty simple things to design? But I'm a little lost and would greatly appreciate the assistance of some individuals more knowledgeable in this field than myself :)

(while I'm aware there are a limited amount of 48VDC LVD available to buy on the market, for the project I'm working on I already have to get a custom PCB made, so I might aswell integrate everything on the single PCB)

Thanks in advance for any assistance :)
 

spec

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POST ISSUE 16 of 2016_12_03 (also see the schematic of post #37 for version 2 of the cutoff circuit using a single shunt reference)

Hello,
I've been browsing around trying to fine a schematic for a 48VDC low volt disconnect. So far I've only turned up LVD's for 12 & 24v schematic.

It would be super if the dropout voltage was adjustable with a pot between 40~50vdc.

From the circuits I've seen they look like pretty simple things to design? But I'm a little lost and would greatly appreciate the assistance of some individuals more knowledgeable in this field than myself :)

(while I'm aware there are a limited amount of 48VDC LVD available to buy on the market, for the project I'm working on I already have to get a custom PCB made, so I might aswell integrate everything on the single PCB)

Thanks in advance for any assistance :)
Hello EF,

Which part of New Zealand are you from. If you put it next to 'Location' on your user page, it will show in the box at the left of your posts. That will help us give you replies to your questions.:)

Below is a precision battery cut-off circuit that has been configured for 48V nominal. I have made various assumptions, but most parameters can be adjusted to suit your requirements as they develop.

Although, strictly speaking, you need to specify the following:
(1) Maximum current that the cut-off circuit is required to supply
(2) Absolute maximum battery voltage
(3) Cut-off voltage
(4) Re-entry voltage
(5) Cut-off voltage adjustment range
(6) Maximum allowable current drain of cut-off circuit

spec

2016_11_07_Iss2_ETO_48V_BATTERY_CUTOFF_VER1.png
ERRATA
(1) Change LED to type Vishay TLLK4401

Circuit Operation and Performance

(1) The cut-off voltage can be set from 46V to 50V by adjusting RV3. This range can be changed if required.
(2) This is a precision circuit and will have negligible voltage drift (at a guess Vcoff +-10mV from 10 Deg C to 50 Deg C)
(3) The hysteresis is presently set to 10% so, if the cut off voltage were set to 48V, the circuit would not cut on until the battery voltage had increased to 52.8V. The hysteresis can be altered by changing the value of R18
(4) The circuit will switch 5A easily (I chose the PMOSFET before knowing how little current you intended to switch) and can switch more current, but I haven't bothered to worked it out. Just a thought but, depending on what you are switching, perhaps you could eliminate the relay.
(5) The LED illuminates when the PMOSFET is turned on. The LED can be removed if not required but it is advisable to still have a 47K resistor connected from the PMOSFET drain to 0V.
(6) The current consumption of the circuit is 48uA (micro Amps) when cut off. This could be reduced. The current consumption will be essentially the same when cut on, except for the additional LED current of 1mA.

Construction and Components

(1) The LED is a high efficiency type (2mA current). The LED brightness can be increased by reducing the value of R19
(2) The schematic shows the pin numbering for the TLV3701ID (SOIC-8 package)
(3) This is a low current, high impedance circuit so the physical layout is critical.
(4) This is a low current, high impedance circuit, so it will need to be protected from contaminates, especially condensation. A varnish conformal coating may even be required, depending on the environment.
(5) This is a low current, high impedance circuit and is susceptible to electromagnetic interference (EMI) so it should not be place in electrostatic or magnetic fields. A metal screening case is advisable.
(6) All resistors, unless otherwise stated (UOS), are metal oxide, 0.250W or more, 5%, or better, thru hole (not surface mount).
(7) RV3 is a multi-turn potentiometer and may not be available in metal oxide (to be advised)
(8) All capacitors are ceramic X7R dielectric UOS, +- 10%, or better. C5 is 10V working minimum. C6 is 60V working minimum. It may be necessary to parallel a number of capacitors to achieve C6 value. C6 can be polypropylene dialectic. Do not be tempted to omit these decoupling capacitors- they are essential for the frequency stability of the circuit.
(9) A snubbing diode is not required for protection to switch inductive loads (relay) because the PMOSFET has a built-in diode that will do the job.
(10) The physical layout must be as shown in the schematic, with special reference to the battery and PMOSFET. Heavy schematic lines indicate heavy wire or printed circuit traces.
(11) R14 is a gate stopper to reduce the chance of the PMOSFET oscillating. R14 also isolates the output of the opamp from the large effective input capacitance of the PMOSFET gate.

Datasheets
http://www.ti.com/lit/ds/symlink/tlv3701.pdf
https://datasheets.maximintegrated.com/en/ds/MAX6006A-MAX6009B.pdf
http://www.vishay.com/docs/62971/sqm100p06-9m3l.pdf
http://www.vishay.com/docs/83343/tlle4401.pdf
 
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MikeMl

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Hello,
I've been browsing around trying to fine a schematic for a 48VDC low volt disconnect. So far I've only turned up LVD's for 12 & 24v schematic.

It would be super if the dropout voltage was adjustable with a pot between 40~50vdc....
How much current can the disconnect circuit draw from the batteries while the voltage is > 48V; presumably you want the current draw to be zero after it has disconnected to protect the batteries?

What load current are you disconnecting?
 

spec

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How much current can the disconnect circuit draw from the batteries while the voltage is > 48V; presumably you want the current draw to be zero after it has disconnected to protect the batteries?

What load current are you disconnecting?
? see post #2.

spec
 
If you are interested in this approach, just post and I will modify the circuit to suit 48V. The modified circuit to suit 48V can probably be simpler too
YES please! :D

What load current are you disconnecting?
the "load" output will be connected to a relay, current draw will only be 50ma, so a small transistor could switch on the relay coil?

presumably you want the current draw to be zero after it has disconnected
if you are thinking of the small amount of power required to operate this circuit and drive the relay, this won't be an issue.

Also Spec do you have a paypal account? I'd like to make a small donation for a beer on me. You've been a tremendous help to me ;)
 

MikeMl

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...the "load" output will be connected to a relay, current draw will only be 50ma, so a small transistor could switch on the relay coil?
Is the 50mA the load current, or the current you expect the relay coil to take. For such a small load current, I wouldn't even use a relay. The relay coil current is likely to be a sizable fraction of the load current...

What is the use model? Do you want to automatically re-connect the load to the battery bank as the voltage increases during charge. If so, at what voltage?

If automatic, then you need some hysteresis between cut-out, and cut-in.

If the use model is manual, then do you want to use a push-button to start the circuit after the batteries are recharged and then have it disconnect the load when the batteries have discharged to a preset voltage?
 
s the 50mA the load current, or the current you expect the relay coil to take. For such a small load current, I wouldn't even use a relay
The 50ma is the relay coil. The load on the batteries is 54amps

the voltage increases during charge. If so, at what voltage
If automatic, then you need some hysteresis between cut-out, and cut-in.
Ah So the IC in Spec's schematic wouldn't reconnect once the voltage is raised?

EDIT: Hope this doesn't mean more work for you Spec? I should have thought about clarifying the need for the circuit to reconnect once the batteries are charged
 
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MikeMl

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The 50ma is the relay coil. The load on the batteries is 54amps...
So to be clear, the relay that switches the load has a 48V 50mA (960Ω) DC coil?

I would recommend that if the cut-out voltage is set to say 42V, then the cut-in voltage should be about 3V higher, say 45V. Without this hysteresis, the relay would constantly cycle on/off because as the load on the battery bank is removed, its terminal voltage will rise just due to the internal resistance of the batteries, which might just pull the relay in again if it were not for the differential between cut-out and cut-in. You may have to have independently adjustable cut-in and cut-out.

Here is an old forum posting about a similar project. It would have to be tweaked a bit for your application. Check the circuit posted in #31.
 
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spec

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So the IC in Spec's schematic wouldn't reconnect once the voltage is raised?
The circuit in post #2 will reconnect when the voltage rises and it also has hysteresis, which can be adjusted as can the cut-off voltage. The circuit has also been built and tested successfully by another ETO member. It is best to discus circuits with their designer/poster to avoid confusion.

spec
 
The circuit in post #2 will reconnect when the voltage rises and it also has hysteresis, which can be adjusted as can the cut-off voltage. The circuit has also been built and tested successfully by another ETO member. It is best to discus circuits with their designer/poster to avoid confusion.

spec
Awesome spec! Can't wait to build this circuit. Has been troubling me, thx so much for your help. And Mike has had great input too thx Mike!
 

spec

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Hi EF,

Post #2 has now been updated with a 48V nominal cut-off schematic and notes. If you have any questions, just ask. :)

spec
 

spec

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(UPDATE: the schematic does show the matching pin numbering- the NOTES now state this)
Thanks again for your efforts Spec, You'll have to forgive me, perhaps this is a noob question? since you're unable to edit the pin numbers on the schematic to match the pins on the TLV3701, how do I determine the correct pin inputs/outputs? (Figured there is a key bit of info I don't know or am overlooking?)
 

spec

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Thanks again for your efforts Spec, You'll have to forgive me, perhaps this is a noob question? since you're unable to edit the pin numbers on the schematic to match the pins on the TLV3701, how do I determine the correct pin inputs/outputs? (Figured there is a key bit of info I don't know or am overlooking?)
:) Perhaps my reply was confusing:
(1) The schematic has always and currently does show the correct pin out for the TLV3701ID (SOIC-8)
(2) The pin out for the TLV3701ID (SOIC-8) is shown on page 3 of the datasheet, linked at the bottom of post #2:

2016_11_08_ETO_TLV3701D_PACK_PINOUT.png
There will be a dot or indent on the package to indicate pin 1.
NC stands for 'No Connection'. NC pins must be left open circuit.

spec
 
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the schematic does show the matching pin numbering
I'd like to say I've had a rough day, but that would be a lie. I read the above as 'doesn't' twice! hahahah. Thanks again spec, I'm ordering the parts now. I'll let you know how it works when assembled!
 

spec

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I'd like to say I've had a rough day, but that would be a lie. I read the above as 'doesn't' twice! hahahah. Thanks again spec, I'm ordering the parts now. I'll let you know how it works when assembled!
The electronics industry has made a complete hash of the pin-outs and package descriptions with about ten different reference numbers for the same package. On data sheets there are package numbers splattered all over the place and it is a hell of a job trying to tie it all together.

Then the manufacturers have these long, arcane part numbers, so you are never quite sure what part to order. Sometimes you think you have ordered a jelly bean diode and a huge rectifier turns up. One of the engineers at work did just that and had boxes of these massive rectifiers hidden under his desk for years- he never lived that down and, of course, we took advantage of his ensnarement; 'I'm just ordering some diodes, Roy- you wouldn't just check the part numbers for me would you Roy?' The real funny thing is that he was a bit sanctimonious and always going on about double checking things and doing it by the book etc etc.:joyful:

spec
 
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