Voltage Sensitive Relay (ACR) w/ high open trigger

[john61ct]

In discussions about separating a LFP House bank from a lead Starter,

members have pointed out that many combiners have their "open" setpoint trigger too low, so that

even after charge sources go offline, the circuits remain connected and Starter could continue to draw current (albeit at a very low rate) from House.

For example, this one
https://www.osculati.com/en/11408-14...ensitive-relay

might seem OK at first, closing at 13.7V (LFP 3.43Vpc), but the hysteresis gap is pretty large, not opening until 12.8V / 3.2Vpc, or where LFP is basically dead flat.

____
So, looking for combiners set at over 13.4V / 3.35Vpv, or

with **adjustable setpoints**, even better.

I'm thinking adjustable setpoint LVC/HVC could do the job too.

Higher ampacities available the better.

[barnakiel]

1) Do not use LFP then.


or



2) Build your own relay that has the sensitivity you demand. Can be done with plain Arduino components.



b.

[john61ct]

Way too late for #1, and there are many many ways to reach the desired objectives.

#2 has reliability issues afaic, but yes that is one of those paths.

There are plenty of other threads open in which such a more general discussion would be appropriate.

This thread's topic is very specific, those not interested in that narrow OTS focus should just ignore it.

[smac999]

why are you physically combing a lead battery with a lfp? I would say that is a big no no. I wouldn't even combine lead with AGM.

you should be using a DC to DC charger to share charge if that is what you are trying to do.

[john61ct]

AGM is lead.

And no, OT here, been beaten to death enough, let it lie or raise it elsewhere please.

[Sailmonkey]

For the minimal demands that are placed on a starter battery, could one not just run a simple timer circuit? Something that will connect the battery to the house for 1-2 hours per day for a top up?

Although this prevents using the lead as an alternator protection sink in the case the bms opens up.......

[barnakiel]

Originally Posted by john61ct

This thread's topic is very specific, those not interested in that narrow OTS focus should just ignore it.

https://www.bluesea.com/products/761...mer_Disconnect


1) connects at 13V (plus signal),



2) Used in timer function disconnects 5 secs after charging stops (and signal absent).


3) Used in (alternative) voltage function disconnects at 12.75 (and signal absent).


4) Used in solenoid function disconnects on signal absent (no time dalay).



Still, as I mentioned before, a plain Bosch relay does the same thing and does not cost the extra $$. (Only the (3) function however).



How close to your demand does this get?


barnakiel

[Cpt Pat]

Originally Posted by smac999

why are you physically combing a lead battery with a lfp? I would say that is a big no no. I wouldn't even combine lead with AGM.

you should be using a DC to DC charger to share charge if that is what you are trying to do.

I've been "combining" AGMs and LFP batteries for years. The arrangement works very well provided you have proper management. During discharge, my LFP batteries are placed in parallel with my AGMs until the bus voltage drops to 12.8 volts, then the LFPs are taken off the bus -- and the AGMs take over from there. The LFPs rest with no load until a charge condition exists. During charge, the LFPs are reconnected to the bus when the bus voltage rises to 13.2 volts (LFPs don't receive substantial charge current below that threshold), and they remain on the bus until they either hit my "stop-charge" SoC (usually 80%) or the bus voltage rises to 14.0 volts - whichever comes first. A high current Schottky steering diode permits discharging the LFPs back into the bus, but prevents further charging until the LFP SoC drops 2 A/H (1% capacity) below the fully charged SoC threshold.

Net result:

1) I didn't have to make any modifications to my charging circuitry, sources, or methods. AGM chargers and PV charge controllers can be set for the AGM charging profile.
2) When the discharge SoC threshold on the LFPs is hit, I don't have a "lights out" disconnect threshold -- instead the AGMs continue to serve my loads, the AGMs take over near their 100% SoC open-circuit voltage (12.8 volts) so they aren't cycled until the LFPs are exhausted (preventing unnecessary cycles), I don't have to have any special charging sources for LPS, and I don't need any wild and crazy kluges like lossy DC-to-DC converters (which are also notorious for generating RFI).

[john61ct]

Again, very specific question here, just looking for device reco's

must have adjustable setpoints, or if fixed, not allow current to flow when voltage is under 13.4V

If you don't have such an answer please just refrain, not looking for "big picture" discussion of the various options or use cases, take that to another thread.

Originally Posted by john61ct

looking for combiners set at over 13.4V / 3.35Vpc, or

with **adjustable setpoints**, even better.

I'm thinking adjustable setpoint LVC/HVC could do the job too.

Higher ampacities available the better.

[john61ct]

Originally Posted by barnakiel

How close to your demand does this get?

Not at all.

And the threshold is very specific, "close" is fine as long as it's a higher voltage, but can't be **any lower** even by 50mV.

[swampbush]

The Victorian Cyrix Li charge vsr will do it. Closes at 13.7 opens at 13.5. I have them installed.Manual-Cyrix-Li-ion-120-A-EN.pdf

[Dsanduril]

Have you seen this one? The adjustment steps are 0.1V, so don't know if that is fine enough for your purpose. The manual is not specific, but presumably you could then set the close/open voltages within 0.1 of each other. Did not look at $.

[john61ct]

Originally Posted by Dsanduril

Have you seen this one? The adjustment steps are 0.1V, so don't know if that is fine enough for your purpose. The manual is not specific, but presumably you could then set the close/open voltages within 0.1 of each other. Did not look at $.

Adjustable, great, will check it out.

Australian gear is usually pricey, but solid. Of course these days could just be relabeled from China 8-)

Thanks

[john61ct]

Originally Posted by swampbush

The Victorian Cyrix Li charge vsr will do it. Closes at 13.7 opens at 13.5

Great, thanks, setpoints just right.

> Closes (combines) at 13.7V / 3.43Vpc, opens (isolates) at 13.5V / 3.38Vpc

Victron of course, Maine Sail expressed reservations on the quality of this line, but if this aspect turns out to be rare, worth overlooking that maybe.

Or newer ones improved. . .

You've had no reliability issues?

[swampbush]

Originally Posted by john61ct

Great, thanks, setpoints just right.

Victron of course, Maine Sail expressed reservations on the quality of this line, but if this aspect turns out to be rare, worth overlooking that maybe.

Or newer ones improved. . .

You've had no reliability issues?

Two of them working fine since the start of this year. My alternators only put out 90 amps max, 50 most of the time so I am not stressing the 120 amp limit.