Voltage Sensitive Relay (ACR) w/ high open trigger

[ramblinrod]

Originally Posted by 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.

Your welcome. ;-)

[john61ct]

This seems to be the OEM for that "Australian" Intervolt unit https://www.manson.com.hk/

Can't tell the difference between these two, and pricing's not listed, except by SA vendors

https://www.manson.com.hk/?s=ssb

SSB-5113
SSB-6113

MB-3688 apparently discontinued

[john61ct]

Very odd unit from our friends at Battle Born

https://www.amazon.com/Battle-Born-B...dp/B07DY8S815/

[Q Xopa]

Originally Posted by 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.

Or you could use a Victron FET Combiner. The batteries are never actually 'joined', There is only current flow FROM your charge source, usually alternator, to the batts. No current can flow FROM the batts.

[john61ct]

Yes, but with one-way devices, you lose the advantage of two-way sensing and current flow, when there are charge sources on both sides.

Unless you double up, one for each direction.

VSR/ACR/combiners only please.

But thanks. . .

[Q Xopa]

Originally Posted by john61ct

Yes, but with one-way devices, you lose the advantage of two-way sensing and current flow, when there are charge sources on both sides.

Unless you double up, one for each direction.

VSR/ACR/combiners only please.

But thanks. . .

If you have a combiner connected to a charge bus with all your chsrge sources connected to it. Then any charge source can charge any battery as you are suggesting.

But if you are sold on only ACR/VSRs then I wont try and talk you out of it.

Good luck.

[john61ct]

No that is not the case,

Just not what this thread is about.

Thanks

[newhaul]

Here ya go this fits all of the parameters for you .
Electronic Battery Isolator | Intervolt

[donradcliffe]

Originally Posted by Cpt Pat

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).

You didn't mention the other substantial benefit--if you hook your charging sources directly to the AGM, you don't have to worry about damage to them if the LFP's disconnect while charging.

I'm working on a friends RV with a combined AGM/LFP system. I was ready to tear out the LFP's and go with straight AGM's until I read your post. I am very interested in the details in how you connect and disconnect the LFP's.

[donradcliffe]

Think a bit more about it, if you had an override disconnect to the LFP's, when you were going to be on dock power for an extended time you could just disconnect them and run the boat on the dock power with the AGM as a voltage stabilizer.

[john61ct]

Originally Posted by newhaul

Here ya go this fits all of the parameters for you .

Electronic Battery Isolator | Intervolt

Yes, #12 & 17, but thanks, there are a few models.

[john61ct]

Originally Posted by donradcliffe

Think a bit more about it

Please discuss these (most excellent) ideas in another thread, or start your own new one - it's free!

[Jetx]

Take a look at the Magnum Smart Battery Combiner here. Only 25 amps capacity (unless you use an external solenoid), but you probably don't need high current capability for keeping a start battery topped up. Also can get away with smaller wiring and fuses than would be needed with a Cyrix or other high-current VSR.

[john61ct]

Different use cases of course require different ampacity levels.

There is no specific use case here, so not limiting to a particular current spec range, obviously higher the better.

But the combiner actually being a true **current limiting** device, still maintaining a reasonable voltage for current transfer / charging while capping the amps at a maximum,

as opposed to the norm of just spec'ing a "do not exceed" upper limit, perhaps requiring an additional fuse or CB,

would be a huge advantage for several scenarios.

So far, I have only seen that feature in units that do not meet the stated voltage requirements.

[john61ct]

Originally Posted by Jetx

Take a look at the Magnum Smart Battery Combiner

So, "Connect" setpoint can be as high as 13.8V / 3.45Vpc, excellent

LVC highest setpoint is 13.5V / 3.38Vpc, also good, a decent margin above resting Full spec of 13.4V 3.35Vpc

The OCP handling behaviour, allowing overcurrent to pass at a lower rate, seems a combination of true current-limiting and hiccup mode for extreme cases, that may be **a big** plus.

24V auto-adjust capability, and an adjustable HVC also! Icing on the cake. . .

Great find, valuable addition to the list, thanks very much!