HVC/LVC Relay current LifePo4

[deandavis1]

Hello, Sorry if this has been covered before. I can't work out how the search system works on CF other than to give me resulting threads which might have hundreds of posts in it.

I am installing a new LifePo4 system and want to include a high and low voltage cutoff circuit (HVC / LVC). The issue is the power these switches take. Assuming I use two normally open contacts I have considered relays, solid state relays and contractors and surprised at the amount of power this would take.

A typical example: two relays on for 24hrs at 150mA is 7.2AH a day. This is about the power output of a 100w solar panel for 1.5hrs.

I also looked at solid state relays which only take about 25mA on the input side but these seem to waste significant power on the output because of the heat generated by the voltage drop (e.g. with 10A running through about 15w).

Products like Tryco EV200 contactors are even worse.

The LVC / HVC circuit break system seems to need a lot of power each day. I'm I looking at this wrong?

Thanks in advance.

dino

[Colin A]

You can try a latching relay. There are arguments to be made that a non latching is safer but as far as reducing current draw a latching will be much better.
http://www.gigavac.com/sites/default...heet/gxl14.pdf
SU280P - Albright International

[deandavis1]

Thanks Colin. These looks like excellent products (although a bit pricey). I'm not sure the second link is a latching relay but I get the idea. I was hoping someone was going to say my maths was wrong (especially with a solid state relay).

I guess if I went this path I would also need to come up with a circuit to convert the output of the BMS to a pulse to drive the relay. Much appreciated.

[dave948]

If you can live with the 2.5 watt consumption:
Thiim BMCD relay does everything you want in one relay.

Thiim A/S

[deandavis1]

Thanks Dave, thats an interesting product. 2.5w @ 12v is about 200mA so unfortunately thats more than an average relay... and very expensive. it also doesn't allow a separate high and low cutoff circuit. so if a LVC event happens it also trips the charging circuit... but its great to know about products like this. thanks.

[dave948]

The only other device I've used is from Redlion the PAXD0010 and the CUB5V. The CUB5V draws about 125ma but gives you the benefit of an LED display (they both do).
Does your existing charger / inverter Controler have settable alarm contacts? All the solutions I've suggested still require a high amperage switching device such as a Hella Marine remote battery switch. Or in your case two if your switching the solar panels separate.

[deandavis1]

Thanks again Dave, The charge sources are solar, alternator and charger. I guess each of this could be made to switch at low levels (good idea for HVC). The load side might need a custom latching circuit. Its sounding more and more like I'll just have to live with 7ah drain each day.

I'm surprised others haven't seen this as an issue before. Especially on a sailing boat.

[deandavis1]

Credit to my father for the following idea. The holding power requirements of a relay can be significantly less than activation requirements. With a relatively simple timer circuit to activate a series resistor there are big power savings to be had. One concern on a boat is potentially rough conditions that would need to be tested but at 7ah a day it sounds like an idea worth exploring... and its cheap.

[travellerw]

Originally Posted by deandavis1

Credit to my father for the following idea. The holding power requirements of a relay can be significantly less than activation requirements. With a relatively simple timer circuit to activate a series resistor there are big power savings to be had. One concern on a boat is potentially rough conditions that would need to be tested but at 7ah a day it sounds like an idea worth exploring... and its cheap.

I can confirm this.. I just tested it with a small 5v relay I had lying around. It takes 0.07a to energize, but will happily stay energized at 0.02a amps. So 1/3 the current draw.

It would be trivial to make a timer circuit to switch the positive side to a resistor to limit the current.

[deandavis1]

For anyone interested there are some good ideas on making a standard relay more efficient here:

What are some ways to use relays more efficiently? - Electrical Engineering Stack Exchange

The bottom line seems to be reasonable to expect approximately a 50% power saving using the above idea. Say about 4ah a day or the output of 1 100w solar panel for an hour. Obviously not as good as a latching relay but food for thought.

[Jd1]

The Tyco EV200 mentioned above is outfitted with an internal economizer (will reduce holding current). It uses 1.7W while holding and you are not likely to find anything that uses less holding power while being heavy enough in current carrying capacity. They use 0.13A for holding !
Be aware that there are identically looking relays WITHOUT the economizer and they use lots more power.
You do not want to use a latching relay as that compromises the whole reason for the relays - safety. You need something that drops out in case of a failure rather than something that depends on a signal to drop it's latched state.
BTW, I use two EV200's but I also have a manual shutdown to disconnect all lithium batteries and power down the relays. In that case I run off a regular lead acid battery. Generally I shut down my lithiums if the boat will sit at it's berth without use for a while.

[smac999]

https://www.bluesea.com/products/cat...s/ML-Solenoids


"Magnetic latching draws no current in "ON" or "OFF" state, only draws current when changing state of switch"


but I think as already mentioned you'd need a pulse. these are controlled by a momentary switch


here is another solenoid at 0.13a


https://www.bluesea.com/products/901...12_24V_DC_250A

[Seman]

Could you use a normally closed contactor instead of normally open. Pick up in LVC or HVC only? Power from your start batterie vor LVC ?

[deandavis1]

Thanks again everyone for all the ideas and insight into what you use.

[wavezest]

Hello LiFePo4-Users

Blue Seas recently came up with a magnetic latching Remote Controlled Battery
Switch, with auto-release:
bluesea.com/products/7713/ML-RBS_Remote_Battery_Switch_with_Manual_Control_Auto-Release_-_12V

It seems to be what we are looking for, with 13mA draw "ON", but it's quite expensive.
Does anyone have experience with that new ML-model?

Your input is very much appreciated