Variable line voltage disconnects - which one?

jacobconroy

Hillbilly of Leisure
I've been using a National Luna Power pack for a couple of years in my JK. However, the voltage disconnect is not variable and the unit is very big. Also, I have a two-bank NOCO charger in the rig. When I plug into shore power at home for battery maintenance I have to manually turn off the power switch on the Power Pack to isolate the batteries. Kindof a pain.

Since I'm always fighting for space I've decided to build my own system from scratch in an effort to move the group 31 deep cycle lower into the space behind the passenger seat. The first step is a variable line voltage disconnect. My requirements and/or druthers would be:
  • That is somewhat small and doesn't cost a million bucks.
  • That the circuit is normally closed between the engine and coach batteries (assuming that the voltage is above the threshold).
  • That it has a remote disconnect function (I plan to use a 120 volt triggered SPDT relay to disconnect the batteries automatically when plugging in to shore power for maintenance/charging OR a diode and 12 volt relay to disconnect the batteries when voltage is sensed from the NOCO charger, but am not sure if this will work).
  • That is has a remote disconnect override function (in case I need to charge the engine battery in an emergency).
  • That the disconnect has voltage trigger options between 12.0 and 12.6 volts (I'd like to play with the exact voltage).
  • It would be nice to have a remote voltage display of some sort for both batteries
I know a lot of you guys are pretty slick with current options and advice would be appreciated. A couple of questions too:
  • What is the general opinion of the correct disconnect voltage? I may not need a variable unit if it has the voltage setting that I need (yet to be determined).
  • What amperage rating should the disconnect be? I think I have a 160 amp alternator.
School me sirs! Thanks.
 

jonyjoe101

Adventurer
I been using these small 5 dollar relays (dc 6-40v battery charger discharger) to connect/disconnect my battery. They are very programmable on whatever voltage (6-40 volts) you want it to trigger the relays. It has a built-in 10 amp relay which I use to trigger a larger 30 amp automotive relay, but will easily trip solenoids. They are very reliable, I have one running nonstop almost 2 years monitoring my lifepo4 battery. The price is low enough you can use several in your system if needed.


503786

these are the parameters it can monitor
Operating mode:

Voltage upper limit: UL1, voltage lower limit nL1, the voltage upper limit is greater than the voltage lower limit (UL1> nL1)

U-1: Charging measurement: When the measured voltage is lower than the lower limit voltage, the relay pulls above; the upper limit voltage, the relay is disconnected.

U-2: charge measurement time control: set the charging time (OP); when the measured voltage is lower than the lower limit voltage, the relay pull, and then start the countdown OP time, the end of the timer, the relay off; when the measured voltage is higher than the upper limit voltage , The relay is disconnected.

U-3: Discharge detection: When the measured voltage is lower than the lower limit voltage, the relay is off, above the upper limit voltage, the relay pulls;

U-4: discharge detection time control: set the discharge time (OP); when the measured voltage is higher than the upper limit voltage, the relay pull, and then start the countdown OP time, the end of the timer, the relay off; when the measured voltage below the lower limit voltage , The relay is disconnected;

U-5: voltage in the range, the relay pull: when the measured voltage between the upper and lower limits, the relay pull, the other circumstances open;

U-6: voltage outside the interval, the relay pull: the measured voltage below the lower limit voltage or higher than the upper limit voltage, the relay pull, the other case the relay is off.
 

jacobconroy

Hillbilly of Leisure
Thanks JonyJoe 101. I like the price point. Do you have a link to buy these or to download documentation?
  • Is the voltage variable to 1/10th of volts? I'd like to try 12.3 for a cutoff point.
  • Is there a trigger to disconnect the circuit (open the relay) remotely from a switch or relay regardless of voltage?
 

dreadlocks

Well-known member

Screw using coil relays, those will draw enough power to be considered a parasitic drain on their own.
 

jacobconroy

Hillbilly of Leisure

Screw using coil relays, those will draw enough power to be considered a parasitic drain on their own.
Well...yeah, if the relay is normally open and you are energizing at camp to utilize both batteries. If you used a normally closed relay it will only be using power when the circuit is cut and hopefully you will have some sort of alarm in that case. If the coach battery is providing current for the relay the starting battery would be safe. A relay shouldn't be using more than 1/10th amp per hour right? Not sure about solenoids.

What other sort of relay is available? Do someone make a solid state disconnect?

That's why I'm asking. Been out of the game for a while. :)
 

dreadlocks

Well-known member
well if you have low voltage and you engage the relay, for a small 10A relay or something its likely a quater to half watt.. not alot yeah, but if its winterized or something this could be fatal to the battery.. if you need a big starter relay or something for high amp loads then your looking at several watts and a significant load.

Solid State relays exist for higher load needs, for low load needs use a mosfet and use it to connect ground.

the one i linked is an off the shelf disconnect thats solid state, its consumption is practically nominal.. it'd take decades to drain my 100AH battery and can handle 100A loads.
 

jacobconroy

Hillbilly of Leisure
Thanks. That answers a lot of my questions. My coach battery will never need to put out more than 5 amps per hour. The only caveat would be if I override the LVD to charge the engine batter (for emergency). Sounds like the Mosfet Victron is what I'm after.
 

luthj

Engineer In Residence
There are numerous mechanical relays with coil economizer type circuits. They use significant power to close, and then the integral (or external) circuit drops the coil voltage down substantially. There are some magnetic latching relays which use no current when latched. You would need one with an integrated logic which switches on/off with a constant signal.
 
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