DC relay operating safety

Thread Starter

yakdaddy

Joined Feb 17, 2024
3
I need help figuring out how to protect a relay from operating while current is applied.
I have 2 LiFePo4 batteries that use a Bus network to activate the voltage output from the BMS. I'm using the same Bus controller to operate both batteries. I'm using one battery as primary power for my load, and one battery as secondary. The issue is that the load can only connect to one battery at a time to avoid a software issue..
I'm using a relay in an unconventional manner to accomplish this. Battery 1 will connect to #87A, Battery 2 will connect to #87, #30 will be the load. Since the batteries output voltage is powered on/off the relay coil will be operated by a 3rd battery, and controlled by a wireless switch.
What I need help with is to keep the relay coil from operating while battery 1 is on and supply voltage is present on #87a.

Any thoughts?
 

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MisterBill2

Joined Jan 23, 2018
18,538
The screen shot indicates a polarity reversal when the relays operate.
In addition, the functional description does not make complete sense to me..
And if there is actually a requirement for interlocking then the wiring diagram shown is not what you need.
 

crutschow

Joined Mar 14, 2008
34,455
Also not sure exactly what you trying to accomplish with that circuit(?).
keep the relay coil from operating while battery 1 is on and supply voltage is present on #87a
What do you mean "battery 1 is on"?
How does it get "on"?
What is "supply voltage"?

How do you expect this to occur for just and the ON and OFF signal from the wireless switch?

Tell us the complete sequence of what you are trying to do with the two batteries and the switch.
 

Reloadron

Joined Jan 15, 2015
7,520
Battery 1 will connect to #87A, Battery 2 will connect to #87, #30 will be the load. Since the batteries output voltage is powered on/off the relay coil will be operated by a 3rd battery, and controlled by a wireless switch.
What I need help with is to keep the relay coil from operating while battery 1 is on and supply voltage is present on #87a.
Your drawing is too small to easily identify the relay pins.
Next, if you are going to use automotive relay pin designations make it clear what the relay is.

Automotive Relay SPDT.png
A much better explenation of your goals would go a long way in helping you, as was mentioned.

Ron
 

Thread Starter

yakdaddy

Joined Feb 17, 2024
3
I'll do my best here....
The relays are being used backwards if you want to think of it that way.
Normally a 12v 5pin relay uses #30 as the supply for positive voltage, or ground connection.
I'm using terminals #87a & #87 as the positive & negative supply from 2 separate batteries, and #30 is used for the load.
The relays coils circuit is powered by battery 3 since battery 1 & 2 will have no voltage output when powered down.

Battery 1, and battery 2 have a Bus network controlled BMS. The load is also part of that Bus network. To avoid a software issue I can only have one battery connected to the load at any given time.
Battery 3 is a normal 12v 10ah LiFePo4. Battery 3 will power the wireless remote. Wireless remote will control the relay coils.
(There is no option to power the relays from battery 1, or battery 2. Their BMS disconnects the outputs of the battery. So no supply voltage when the battery is powered off. )

Battery 1 -
Positive to relay 1 #87a nc
Negative to relay 2 #87a nc

Battery 2 -
Positive to relay 1 #87 no
Negative to relay 2 #87 no

Load + to relay 1 #30
Load - to relay 2 #30

Relay 1 & 2 coils controlled by wireless remote. Wireless remote powered by battery 3.

I've wired this circuit a dozen times in the past, but those were all using 2 standard 12v sla batteries. This circuit allows a load to connect to battery 1 by default through #87a. When the relays coils are energized the load will connect to battery 2 through the #87 terminal. It works, I've used it, that's not the issue.

In this situation the batteries have a BMS that will power down, and there will be no battery output or supply voltage. This needs to occur to protect the battery, and the load from a network error. I need to add some sort of safety to keep the relay coils circuit from energizing while the relay terminal #87a still has voltage present from battery 1.

I don't know how to explain it any better.
 

jrb_sland

Joined Dec 24, 2021
24
I'll do my best here....
The relays are being used backwards if you want to think of it that way.
Normally a 12v 5pin relay uses #30 as the supply for positive voltage, or ground connection.
I'm using terminals #87a & #87 as the positive & negative supply from 2 separate batteries, and #30 is used for the load.
The relays coils circuit is powered by battery 3 since battery 1 & 2 will have no voltage output when powered down.

Battery 1, and battery 2 have a Bus network controlled BMS. The load is also part of that Bus network. To avoid a software issue I can only have one battery connected to the load at any given time.
Battery 3 is a normal 12v 10ah LiFePo4. Battery 3 will power the wireless remote. Wireless remote will control the relay coils.
(There is no option to power the relays from battery 1, or battery 2. Their BMS disconnects the outputs of the battery. So no supply voltage when the battery is powered off. )

Battery 1 -
Positive to relay 1 #87a nc
Negative to relay 2 #87a nc

Battery 2 -
Positive to relay 1 #87 no
Negative to relay 2 #87 no

Load + to relay 1 #30
Load - to relay 2 #30

Relay 1 & 2 coils controlled by wireless remote. Wireless remote powered by battery 3.

I've wired this circuit a dozen times in the past, but those were all using 2 standard 12v sla batteries. This circuit allows a load to connect to battery 1 by default through #87a. When the relays coils are energized the load will connect to battery 2 through the #87 terminal. It works, I've used it, that's not the issue.

In this situation the batteries have a BMS that will power down, and there will be no battery output or supply voltage. This needs to occur to protect the battery, and the load from a network error. I need to add some sort of safety to keep the relay coils circuit from energizing while the relay terminal #87a still has voltage present from battery 1.

I don't know how to explain it any better.
I cannot visualize a relay when you refer only to specific pin numbers of some anonymous unit. It would help enormously if you would provide a schematic of the circuit that works using SLA batteries. A pencil sketch would be sufficient. In any event, my first suggestion would be to keep that circuit, INCLUDING a pair of small SLA batteries, then add one each of your preferred LiFePO4 batteries in parallel with each of the two SLA batteries. The SLAs will provide supply to coast through those times when the relays aren't active.
Your problem seems to be entirely with your choice of batteries fitted with over-protective BMS units. Perhaps you might seek (or assemble yourself from discrete cells) LiFePO4 batteries that do NOT shut themselves off. How are the batteries recharged? Do the two batteries have a common ground/low side/neutral connection, in which case why would you use two relays if you could simply switch between either of the two + terminals? And in that case, could you not eliminate the relays entirely & simply use two appropriately sized diodes to allow only the battery with the higher charge level to provide power at any instant? Again, PLEASE provide a sketch of the wiring of your original [working] circuit so we might better understand your problem. Thanks in advance.
 

Irving

Joined Jan 30, 2016
3,890
There are many ways to do this but the absolute simplest is another small relay, coil between relay1 87a and relay2 87a. when power on 87a this relay will be powered on. A NC contact in series with the changeover relay coil will stop it being powered until 87a is dead.

1708191156339.png
 

MisterBill2

Joined Jan 23, 2018
18,538
What I see is that there are two SLA batteries connected to the relays, such that one battery is connected, both positive and negative sides, to the load, when both relays are not energized. The relay coils are connected IN SERIES so that they can both operate at the same time. When the relays are operated both positive and negative connections transfer to the other SLA battery.
But evidently these are not SLA batteries, because "they can be powered down" by some sort of network that instructs a BMS package to switch them off. Normal batteries do not ever switch off, but they do become discharged.. So now the mystery is what must and must not be allowed to happen while one or both of these batteries are "switched o" or "switched off"

And aside from that information I am also wondering why both sides of a battery need to be transferred, since usually, many multiple battery systems share connections to an unswitched negative common circuit.

So now it would be handy to have a explanation of what connections are desired under which condition, and what connections must not happen, under what conditions. These descriptions will not include contact designations, just descriptions such as: Battery 1 positive, battery #1 negative, Load positive, load negative, and whatever conditions apply.
My problem is a lack of ability to read the minds of others and understand their perceptions. A serious handicap indeed it is.
 

Irving

Joined Jan 30, 2016
3,890
My problem is a lack of ability to read the minds of others and understand their perceptions. A serious handicap indeed it is.
It seems to be a common failing around here sometimes ;)

Or maybe its my many years of interpreting the random delusions of many clients that allows me to extract that nugget of information from their ramblings....

And aside from that information I am also wondering why both sides of a battery need to be transferred, since usually, many multiple battery systems share connections to an unswitched negative common circuit.
You're right, but I didn't want to change what the TS said.... for now.

The relay coils are connected IN SERIES so that they can both operate at the same time.
Umm, no, Rly1 & Rly2 are in PARALLEL.... [edit] in my drawing, but in series in the original, my bad. However if these are 12v automotive relays then they have to be in parallel if Battery 3 is a 12v LIFEPO4 as stated by the TS.
 
Last edited:

crutschow

Joined Mar 14, 2008
34,455
Why not use one SPDT relay to connect the two batteries?
Each battery goes to one of the two contact connections, and the output is from the relay wiper.
The unenergized relay will connect one battery, and the energized relay will connect the other, without there being a possibility of both being connected at the same time.
 

Irving

Joined Jan 30, 2016
3,890
Why not use one SPDT relay to connect the two batteries?
Each battery goes to one of the two contact connections, and the output is from the relay wiper.
The unenergized relay will connect one battery, and the energized relay will connect the other, without there being a possibility of both being connected at the same time.
I'm sure that's probably right, but the key point wasn't that they can't be connected at the same time, but that the transfer cant happen if battery 1 is still active. That's the oddity here because normally you'd want to switch BEFORE battery1 died!
 

MisterBill2

Joined Jan 23, 2018
18,538
It seems to be a common failing around here sometimes ;)
Response to post #9:
Or maybe its my many years of interpreting the random delusions of many clients that allows me to extract that nugget of information from their ramblings....



You're right, but I didn't want to change what the TS said.... for now.


Umm, no, Rly1 & Rly2 are in PARALLEL.... [edit] in my drawing, but in series in the original, my bad. However if these are 12v automotive relays then they have to be in parallel if Battery 3 is a 12v LIFEPO4 as stated by the TS.
Observe the wiring diagram in post #1, terminal 86 on one ties to terminal 85 on the other and the external wireless control is across the other terminals. As in series as it can be. In that suggested alternative they are indeed in parallel.

And clearly there is something that we have not yet been told.
 

Irving

Joined Jan 30, 2016
3,890
Observe the wiring diagram in post #1, terminal 86 on one ties to terminal 85 on the other and the external wireless control is across the other terminals. As in series as it can be. In that suggested alternative they are indeed in parallel.

And clearly there is something that we have not yet been told.
Yeah, I picked that up and edited my post accordingly. I don't think the TS was thinking straight when he did that sketch, observe that one possible interpretation reverses the battery polarity when switched...
 

crutschow

Joined Mar 14, 2008
34,455
I need to add some sort of safety to keep the relay coils circuit from energizing while the relay terminal #87a still has voltage present from battery 1.
Here's a circuit that adds a couple transistors with one relay to keep the relay from energizing to connect B2 if B1 has voltage.
Does that do what you want?

1708199925078.png
 

MisterBill2

Joined Jan 23, 2018
18,538
Yeah, I picked that up and edited my post accordingly. I don't think the TS was thinking straight when he did that sketch, observe that one possible interpretation reverses the battery polarity when switched...
I did notice that, it is what is shown, which might not be what is intended.
 

Thread Starter

yakdaddy

Joined Feb 17, 2024
3
The batteries are not basic by any means, they are 30vdc LMFP. The batteries are controlled by a Bus network at 5vdc, and for that reason they can not be allowed to connect to the load at the same time. This would cause the network to error out when the system sees 2 network ID's trying to connect at the same time. This is a two fold issue since the network could error out if the switch between batteries were to occur while either battery is still powered on.
Each battery has 2 positive terminals, 2 negative terminals, 5 load network terminals , and 5 load controller terminals.

Conventionally I would have the load cable, and load controller cables connected to one battery. The load cable contains 2 positive terminals, 2 negative terminals, and 5 load network terminals. The load controller cable contains 5 network terminals. The controller also operates the battery BMS power cycle, or on/off operation.

The goal is the ability to remotely switch between 2 batteries. This system is on an electric outboard motor, and for some applications the battery is not easily accessible to manually disconnect from one battery and connect to the second battery.
My idea is to use 4 SPDT 36vdc relays for the motor battery circuit, and 5 SPDT 6vdc relays for the motor network circuits. The motor load controller circuit will have 5 SPDT 6vdc relays. That is a total of 14 relays. I'll try to sketch a more detailed circuit diagram tomorrow.
 

MisterBill2

Joined Jan 23, 2018
18,538
The batteries are not basic by any means, they are 30vdc LMFP. The batteries are controlled by a Bus network at 5vdc, and for that reason they can not be allowed to connect to the load at the same time. This would cause the network to error out when the system sees 2 network ID's trying to connect at the same time. This is a two fold issue since the network could error out if the switch between batteries were to occur while either battery is still powered on.
Each battery has 2 positive terminals, 2 negative terminals, 5 load network terminals , and 5 load controller terminals.

Conventionally I would have the load cable, and load controller cables connected to one battery. The load cable contains 2 positive terminals, 2 negative terminals, and 5 load network terminals. The load controller cable contains 5 network terminals. The controller also operates the battery BMS power cycle, or on/off operation.

The goal is the ability to remotely switch between 2 batteries. This system is on an electric outboard motor, and for some applications the battery is not easily accessible to manually disconnect from one battery and connect to the second battery.
My idea is to use 4 SPDT 36vdc relays for the motor battery circuit, and 5 SPDT 6vdc relays for the motor network circuits. The motor load controller circuit will have 5 SPDT 6vdc relays. That is a total of 14 relays. I'll try to sketch a more detailed circuit diagram tomorrow.
OK, So these are actually network controlled power packs with integral batteries.
More questions then: are the battery packs able to deliver the required power through just one set of output terminals, or is there an internal split somehow? Or are the two pairs simply in parallel? That matters quite a lot. Also, quite probably the battery negative terminals could all be directly connected to the power system negative common side, so that only the positive side will need to be switched.
At that point I see a question about timing. Is there an issue with switching the battery connection first and then switching the controls connections? Or can they be allowed to switch at close to the same time? Certainly switching at the about the same time will be simpler and cost less, besides being more reliable.
So now there are additional questions to answer, because just guessing will often not be perfectly correct.

Next, for the five conductor network connection, I am guessing that one of those 5 wires is a common, probably a shield/common connection, which can be left connected between the two battery packs. That would leave you with four connections to be switched, and there are some very good four-pole double throw relays available.
 

jrb_sland

Joined Dec 24, 2021
24
The batteries are not basic by any means, they are 30vdc LMFP. The batteries are controlled by a Bus network at 5vdc, and for that reason they can not be allowed to connect to the load at the same time. This would cause the network to error out when the system sees 2 network ID's trying to connect at the same time. This is a two fold issue since the network could error out if the switch between batteries were to occur while either battery is still powered on.
Each battery has 2 positive terminals, 2 negative terminals, 5 load network terminals , and 5 load controller terminals.

Conventionally I would have the load cable, and load controller cables connected to one battery. The load cable contains 2 positive terminals, 2 negative terminals, and 5 load network terminals. The load controller cable contains 5 network terminals. The controller also operates the battery BMS power cycle, or on/off operation.

The goal is the ability to remotely switch between 2 batteries. This system is on an electric outboard motor, and for some applications the battery is not easily accessible to manually disconnect from one battery and connect to the second battery.
My idea is to use 4 SPDT 36vdc relays for the motor battery circuit, and 5 SPDT 6vdc relays for the motor network circuits. The motor load controller circuit will have 5 SPDT 6vdc relays. That is a total of 14 relays. I'll try to sketch a more detailed circuit diagram tomorrow.
I'd suggest you spend more quality time thinking clearly about what you are attempting to accomplish. You've now upped the ante from 3 to 14 relays! There must be an easier, less complex way to do this, but I refuse to assist if you continue to withhold ANY of the details from us. Would it not make more sense to permanently parallel your two discrete battery units, then connect this single super-battery to the load? Would that not obviate your apparent need for TWO network addresses? WHY is your network not tolerant of battery switching? Can this not be dealt with in software {a timeout pause after commanding the switchover, for instance?} Context is essential, not a luxury. For instance, is the boat manned or a drone? Or perhaps a submarine? Or is this an outboard motor running in a barrel for some science experiment? Tell us more!! Some outstanding [not yet answered] questions:
1/ How are the storage batteries to be recharged?
2/ Can the two nominal 30 volt battery packs have a common negative connection? If not, why not?
3/ What do you mean by the word "network"?
4/ Is this a personal project or are you doing it for money?
5/ Is the nominal 30V battery pack a commercial product, or of your own design/assembly? If commercial, please point to the manufacturer's website, and provide us with the specific product part number or the like.
6/ Will your load [an electric outboard motor for a boat of some kind?] tolerate the multi-millisecond power dropout when the load relay change state, or will you need a large holdup capacitor across the output?
7/ Motor loads are notoriously inductive - will your relay contacts survive the inevitable arcing during changeover, or will your "system" only change batteries with the motor powered down?
 

MisterBill2

Joined Jan 23, 2018
18,538
I'd suggest you spend more quality time thinking clearly about what you are attempting to accomplish. You've now upped the ante from 3 to 14 relays! There must be an easier, less complex way to do this, but I refuse to assist if you continue to withhold ANY of the details from us. Would it not make more sense to permanently parallel your two discrete battery units, then connect this single super-battery to the load? Would that not obviate your apparent need for TWO network addresses? WHY is your network not tolerant of battery switching? Can this not be dealt with in software {a timeout pause after commanding the switchover, for instance?} Context is essential, not a luxury. For instance, is the boat manned or a drone? Or perhaps a submarine? Or is this an outboard motor running in a barrel for some science experiment? Tell us more!! Some outstanding [not yet answered] questions:
1/ How are the storage batteries to be recharged?
2/ Can the two nominal 30 volt battery packs have a common negative connection? If not, why not?
3/ What do you mean by the word "network"?
4/ Is this a personal project or are you doing it for money?
5/ Is the nominal 30V battery pack a commercial product, or of your own design/assembly? If commercial, please point to the manufacturer's website, and provide us with the specific product part number or the like.
6/ Will your load [an electric outboard motor for a boat of some kind?] tolerate the multi-millisecond power dropout when the load relay change state, or will you need a large holdup capacitor across the output?
7/ Motor loads are notoriously inductive - will your relay contacts survive the inevitable arcing during changeover, or will your "system" only change batteries with the motor powered down?
See the answers to the questions I posed in post#17! I reduced it to one 4 pole double pole relay and two SPST power relays. There is no reason the TS should be restricted to one particular type of relays, other than not having checked a better source. Also there may be a level of technical skill that I am not familiar to conversing with.
 
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