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Old 02-05-2016, 19:20   #1
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Which Is The Most Power Savvy Relay?

Hi all this is my first post in the forum!
I am assembling a 12V LIFEPO4 system for a conversion van, it'll be a small bank ( 200 - 400 AH). I know this form is not for RV's, but you guys are so much more knowledgeable in LIFEPO4 than any other resource i've found!!!!
The Battery Management System will drive,through.... RELAYS, some low amperage ( <1 AMP) components like a buzzer, and a blue sea 7713 contactor. (https://www.bluesea.com/products/771...-Release_-_12V),

As i look into relays, i realize that they can be very power hungry.
E.G. http://www.amazon.com/Vehicle-Contac...LAY+10+AMPERES
The above relay consumes 150mA. Apparently it's nothing, but if you consider the consumption in a week: 150 x 24 x 7 = 25 AMperes TOTAL.

since the relays will be an essential part of my BMS, i can't not have them.

DO you have any ideas on relays that can consume less poower????

These are my ideas , please let me know which sound best or if you have a better suggestion???

- I have seen solid state relays, like this, https://www.waytekwire.com/item/7553...-State-Relay-/, and they seem to consume less power ( GOOOD!!!) but i have read over the web that they 'leak'. SInce the bms needs to make sure that it totally cuts down the consumption ( zero amps), i can't use these type of relays.

- I have seen reed relays and electronic ones, ( FOR PCB ) for example this one ELECTROL - BBV1A12A10 - Relay, reed. Input: DC. Contacts: SPST NO. , looked into their specs, and they could work for my purposes, since i need to switch <1 ampere of loads. BUT, the reed relays are tiny and for PCB's. DO i NEED to deal with soldering and PCB construction??? i have never soldered !!!!!!!!!! Is this the best way to go???? Can i order online to someone to put this circuit together for me?

THANKS EVERYONE IN ADVANCEEE!!!!!

-
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Old 03-05-2016, 01:37   #2
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Re: Which Is The Most Power Savvy Relay?

Search for a latching relay. Will have magnetic contacts. Pulse on,off, zero holding current.
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Old 03-05-2016, 13:47   #3
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Re: Which Is The Most Power Savvy Relay?

Quote:
Originally Posted by poiu View Post
Search for a latching relay. Will have magnetic contacts. Pulse on,off, zero holding current.
Latching relays will not work in this sort of a BMS setup.
Look at the thread of 'LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks' for everything you ever wanted to know about lithium storage and where afraid to ask .....
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Old 04-05-2016, 10:07   #4
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Re: Which Is The Most Power Savvy Relay?

1mA x 24 = 24mAh, or .024Ah per day. Not very much. Depending on how you design your system you could go with a normally open or a normally closed relay. They don't use power when NO or NC. Of course some designs and systems would prefer one over the other so you may be stuck with using the power, but it is much lower than you calculated: 150mA x24 x 7 = 0.84Ah per week.
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Old 04-05-2016, 18:19   #5
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Re: Which Is The Most Power Savvy Relay?

Quote:
Originally Posted by poiu View Post
Search for a latching relay. Will have magnetic contacts. Pulse on,off, zero holding current.
THanks for your answer, I have been looking into latching relays but they need like a momentary signal.

My BMS has a constant +12 v output when there is no alarm, and drops to GND when there is an alarm condition.

ALso, the BMS has a max of 2AMPrms and 4 amp peak.

Most of the latching relays i've found are relatively for bigger currents ( say 50A+) , but have not found any smaller. Do you think there could be small current latching relays ( say 2 - 5 or 10 amp)????

Thanks !!!
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Old 04-05-2016, 18:21   #6
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Re: Which Is The Most Power Savvy Relay?

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Originally Posted by Jd1 View Post
Latching relays will not work in this sort of a BMS setup.
Look at the thread of 'LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks' for everything you ever wanted to know about lithium storage and where afraid to ask .....
THanks.
I am strongly considering spending 1 or 2 days going trhough the 5000+ replies

I'm sure I'll gain all the knowledge that i need.
Thanks for the advice.
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Old 04-05-2016, 18:30   #7
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Re: Which Is The Most Power Savvy Relay?

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Originally Posted by exMaggieDrum View Post
1mA x 24 = 24mAh, or .024Ah per day. Not very much. Depending on how you design your system you could go with a normally open or a normally closed relay. They don't use power when NO or NC. Of course some designs and systems would prefer one over the other so you may be stuck with using the power, but it is much lower than you calculated: 150mA x24 x 7 = 0.84Ah per week.
Hello. exMaggieDrum, thanks for answering!!!
You mention at the beginning 1mA, is that from a relay that you use???

Unfortunately my system design needs to have something consuming power, because +12V is non alarm condition and GND is alarm condition :S:SS

My calculation is like this : 0.150 * 24 * 7 = 25.2, so i think by the end of the week, the relay itself has sucked 25.2Ah from the battery. Can you please share with me how did you get the 0.84Ah per week??? I am very new at this so i could be missing a point or 2.


Thanks for your reply !!!!!
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Old 04-05-2016, 21:22   #8
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Re: Which Is The Most Power Savvy Relay?

When you originally posed the question, I somehow thought that what you were after are the normal power relays that everyone uses for a lithium bank. These are the relays for charging current, load current and emergency shutdown. I am not sure what it is that you are switching at less than an amp but my original answer was geared towards the high power relays.
For low power relays, I would simply go to the Digikey web site and select the right device with the right contact arrangement, the right power (the amount you can live with) and the connection method (maybe a socket mounted relay where the matching socket has screw type connections for your leads).
My system is using a House Power BMS and there are only high power relays which are costly in $ and amps. I have not found a way around the considerable power drain other than to use a relay with an 'economizer' built in. These relays use a high current for switching but a much lower current for holding the relay. Note that they are NOT latching because latching defeats the purpose for which they are used in the system.

Good luck !
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Old 05-05-2016, 09:35   #9
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Re: Which Is The Most Power Savvy Relay?

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Originally Posted by isaacchacon View Post
Hello. exMaggieDrum, thanks for answering!!!
You mention at the beginning 1mA, is that from a relay that you use???

Unfortunately my system design needs to have something consuming power, because +12V is non alarm condition and GND is alarm condition :S:SS

My calculation is like this : 0.150 * 24 * 7 = 25.2, so i think by the end of the week, the relay itself has sucked 25.2Ah from the battery. Can you please share with me how did you get the 0.84Ah per week??? I am very new at this so i could be missing a point or 2.


Thanks for your reply !!!!!
Duh - you are correct.

Have you considered putting a small solar panel on as a charging source. You could put it through the high voltage cutoff relay so it wouldn't overcharge your cells. It could provide enough amps to replace the Ah used by the relays.
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Old 08-05-2016, 18:29   #10
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Re: Which Is The Most Power Savvy Relay?

I am adding an idle question here. Doesn't anyone make a switch operated by a tiny electric motor or a solenoid for that matter, where the motor or solenoid is only on while switching? Energise terminal A, bzzzt or click, switch is on. Energise terminal B, bzzzt or click, switch is off. A typical battery selector switch could be motorised. Or rather, doesn't any one make one reasonably priced?
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Old 09-05-2016, 00:56   #11
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Re: Which Is The Most Power Savvy Relay?

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Originally Posted by sv.antea View Post
... Doesn't anyone make a switch operated by a tiny electric motor ...
Yes, they are called motorised switches, but are normally bulky.
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Old 26-06-2016, 16:09   #12
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Re: Which Is The Most Power Savvy Relay?

I may have found a good candidate to be named 'power savvy' relay.

It is small, but it is good enough for my needs. I just got it and been testing it for the last day. We still need to see if it can endure continous duty for several years without breaking!!!

It's name is ELK 912 , it does not come insultaed but it does the work.

I just tested it with my multi.

Common Automotive relay energy consumption: .130 amperes @ 12V
ELK912 : 0.030 amperes @ 12V.

You may think I am looking at the tiny detail but this difference gets magnified after some time:

Common automotive relay consumptin in a week: 25 AMP
ELK 912 consumption in a week : 0.030*24*7 = 5 AMPS!!!!!!!

If you consider the cost of your batteries ( like mine, expensive lithium), and considering all the amps that you will save over the life of the battery, this relay may pay for itself!!!!


THe relay was less than ten dollars .
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Old 27-06-2016, 02:22   #13
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Re: Which Is The Most Power Savvy Relay?

So what you are saying is that you have found a standard 400Ω relay?

All these are 400Ω and above, but it depends what contact current you need.
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Old 27-06-2016, 07:37   #14
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Re: Which Is The Most Power Savvy Relay?

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So what you are saying is that you have found a standard 400Ω relay?

All these are 400Ω and above, but it depends what contact current you need.
I am unsure about the resistance of the elk912, but sounds like you know relay classification better than me.

The big advantage i see on this vs the ones in your link, is that I don't have to solder or build the pcb, since it comes ready to connect with screws.

I am no electrical engineer as you may have guessed by my posts

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Old 27-06-2016, 08:16   #15
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Re: Which Is The Most Power Savvy Relay?

I took a look at the elk912 relays and have ordered some to play with and may use. They look like they will work fine for the minimal amps needed to switch the larger high amp contactors.

I am probably going to use the Blue Sea 7713 remote battery switch, a contactor with some extras. It is more expensive but it has a remote switch capability and the ability to completely override by a manual switch on the 7713. I think the elk912 compares to most of the small automotive style Form C relays. It will not handle big amps. I think the 7713 requires 7amps max for 20ms and 13mA when energized closed from normally open.

It is a normally open relay with a magnetic latch but is auto-releasing, i.e. no power to the control circuit. The magnetic latching basically just lessens the power to keep it closed after it is closed at the higher quick power. Or you can manually lock it on (closed) or lock it off if you need to work on something without the battery connected to the rest of the system.

I am going to use one of the automotive style 5-pin Form C relays for disconnecting my solar charging (60A max). I am going to use either a 70A or 80A relay for this. The elk912 could not handle this at all. I don't need a big contactor for this level of power. My load side contactor is equivalent to the EV200 which seems to be the most recommended and installed contactor. My alternator output (up to 275A on the DC genset) will be connected to the main bus but I am putting in secondary relays to shut off the fields for an HVC event.
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