ACRs and LFPs

[DDW]

Is anyone using ACRs in a system with LFPs, and have you made it work?

The problem with the Blue Seas ones at least, is the voltages for combine and disconnect are appropriate for flooded lead acid, and perhaps not much else. I've got one in between two Lifeline AGMs and it is even set too low for that. The fully charged Lifelines sit at about 13.0V until loaded some, that is high enough to turn the relay on. This leads to all sorts of unwanted behavior. An LFP or mixed system will be worse, as the LFP sits at around 13.3V.

Blue Seas used to make ACRs with adjustable thresholds, perhaps others (Sterling?) still do. The system I am looking at right now has a couple of ACRs to combine house and engine, and house and bow thruster batteries. To change the house to LFP seems like it will require abandoning those and using either FET isolators or DC-DC boost buck converters, each of which has its own issues.

Unless someone has learned how to hack the Blue Seas ACRs and set them up to say 13.5V

 

[Portage_Bay]

Someone on TF a while back mentioned Egis ACR that is programmable. Might be worth looking into

 

[SteveK]

From Marine How To
WARNING: ACR’s are not for use with LiFePO4 Batteries!

 

[Insequent]

I was using Blue Seas ACR's when both house bank and start batteries were AGM. Alternators charged large house bank. The ACR's seemed to work OK but I never got into the weeds ...

When i installed an LFP house bank, with alternators still charging that bank using a new profile, I turned the ACR's off and covered with a label "Emergency Use Only". Just in case I had a totally flat house bank (which has happened once) and I need a little bit of charge in it for the shore power charger to start charging. The ACR's only needed to be on for a very short period, and were then turned off. I charge the AGM start batteries via DC-DC chargers from the house bank.

 

[Iggy]

Someone on TF a while back mentioned Egis ACR that is programmable. Might be worth looking into

Yes, you can set the voltages.

XD Single - Programmable ACR w/Knob - Tinned Wires, Bulk Pack

www.egismobile.com

I used one of these as a remote battery switch. Very good support when I called them. What I really like is that the large battery terminals face out, not down.

 

[rslifkin]

I swapped out my ACRs for DC-DC chargers in my recent LFP install. In both cases, with the ACRs and the DC-DC chargers I had them interlocked with the ignition switches. I didn't want the batteries combined with the engines off, or the DC-DC chargers to siphon power from the start battery charger (and mess up accounting of where power came from), so I specifically used ACRs and DC-DC chargers with the ability to have them enabled when the key is on, disabled when it's off.

 

[Bmarler]

From Marine How To
WARNING: ACR’s are not for use with LiFePO4 Batteries!

Any explanation to go with that? Has technology changed since then?
I don’t think I’d use an ACR just because the inrush current could be so high.

I guess I should actually say the discharge current from a lifepo4 would be high until the voltages closed in on each other. Not really “inrush” current. Knowledge of the bms capacity would be necessary.

 

[SteveK]

Any explanation to go with that? Has technology changed since then?
I don’t think I’d use an ACR just because the inrush current could be so high.

I have inserted the link to article in post 3.
Mostly to do with the automatic switching voltage 13V is below the standing voltage 13.3-13.5V of LFP batteries so a house bank may drain into start battery.
May as well use a 1-2-ALL switch and leave it on 'ALL'

 

[HeadedToTexas]

I swapped out my ACRs for DC-DC chargers in my recent LFP install.

I will be doing this as well for two reasons. First, the DC-DC solution tells you what is happening via Bluetooth and offers this wealth of information where the ACR does not (or at least my old Blue Sea models don't). And second, the DC-DC chargers cost virtually the same as new Blue Sea ACRs. My 2¢.

 

[DDW]

Any explanation to go with that? Has technology changed since then?
I don’t think I’d use an ACR just because the inrush current could be so high.

The inrush problem, when paralleling either two LFPs or a mixed system has been raised in aircraft systems. Of course the details matter, but I tested this (in an aircraft) and the inrush was far less than you might imagine. It is true that the potential for large currents might exist, when paralleling a fully charged and a depleted battery. But in fact the measured current was modest, because the charged battery voltage is pulled down a little by the load and the depleted battery is raised a lot. In the aircraft, paralleling two 20 AH batteries produced about the same inrush as switching on the VHF radio.

 

[DDW]

DC-DC converters are not a direct replacement for an ACR in at least some cases. They are one way devices, and very limited in current. Also in the Victron ecosystem, they do not report much of what they are doing.

The XD version looks interesting, but still cannot be used in a mixed LFP/AGM system or any LFP system. The turn off voltage cannot be set high enough - only to 12.7, that would be a fairly well depleted LFP. You need turn on to be set at perhaps 13.6 or 13.7, and turn off to be set at 13.4 or 13.4. Otherwise the LFP side will keep it on all the time.

Ignition controlled contactors is what I eventually went to even in my AGM system, to keep the ACR from constantly cycling on and off. This also has issues: when the ignition is turned on, you are connecting a potentially depleted house bank to a full start bank, before the engine is started. Not ideal. And does not account for other sources of charge.

May have to build something myself.

 

[SteveK]

DC-DC converters are not a direct replacement for an ACR in at least some cases. They are one way devices, and very limited in current.

If you need two way, install one in each direction. I don't want my start battery to deplete so if you do make sure an ignition run feed turns on the DC2DC from both.

 

[rslifkin]

Also in the Victron ecosystem, they do not report much of what they are doing.

The older ones don't, but the newer Orion XS models report much more data, are much more configurable, and can also have a remote trigger input so you can interlock them to the ignition if desired. The way mine are configured and wired, they only transfer power from start -> house with ignition switch on and voltage high enough to indicate charging on the start battery (so they won't engage at key on before engine start unless the start battery shore charger is running).

The BEP/Marinco ACRs (they call them a DVSR) I was using previously also had a remote trigger / sense wire, so I had them hooked to the ignition. Similarly they would only engage with key on and sufficient voltage (and after a few second delay). In practice, assuming shore power was shut down before starting, they'd engage about 5 seconds after the engine was running.

I haven't worried about bi-directional charging in my setup, the DC-DC chargers (and the ACRs before them) are only there to feed alternator power to the house bank. There's a separate 120V charger for the start batteries that runs on shore or generator power. And nothing runs from the start batteries with the engines off, so if we sit for a couple of days with no shore power and don't run the generator, the lack of charging to the start batteries is a non-issue.

 

[CharlieJ]

Most installers that are using an external alternator regulator to protect the alternator from the harsh demands of charging a LFP house bank use a DC/DC charger between the LA start battery and the LFP house bank. The “dumb” alternator charges the LA start battery and the DC/DC charger then is adjusted to limit the charge current allowed to flow to the LFP house battery. Typically the limit is set to keep the temperature of the alternator when going all out to be < 100C.

An ACR has no regulating capability; it is on or off. The ACR therefore negates the benefit of the DC/DC and the alternator is unprotected from being over stressed.

 

[DDW]

The Orion XS looks like it might solve some of my issues, albeit a little pricey. I hadn't noticed that it has a VE.direct port (none of their others do), so part of the ecosystem.

One thing it won't do is share a load. The common arrangement (on this model boat anyway) is to connect the stern thruster to the starter battery. With an ACR to the house, while the engine is running and alternator charging (normal when the thruster is used), there is a high current path to allow the house to assist in the very high current draw (but very low energy draw) of thruster use. Replacing that with a DC-DC eliminates that feature. The bow thruster has its own battery, charged with an ACR and smaller gage wires, so it always had that problem - but isn't connected to any other voltage sensitive equipment (engine ECU, electronic throttle/shift, nav instruments, etc).

Another issue is the current capacity is limited for charging. If the DC-DC is charging the engine and alternator connected to the house, then a house LFP disconnect *may* blow the alternator. If the DC-DC is charging the house and alternator connected to the engine AGM, the charge to the house is severely limited unless perhaps three Orions are paralleled. I get >100A continuous into even my current AGM house bank.

All of those problems are pretty well solved by an ACR, if only it was set for the right voltages (or a contactor turned on at the right times).

An externally regulated alternator is a given in this type of system. Doesn't really change any of the other issues.

 

[CharlieJ]

@DDW

One thing it won't do is share a load. The common arrangement (on this model boat anyway) is to connect the stern thruster to the starter battery.

The starting battery, if the alternator has been running for more than about 5 minutes, is fully charged and is fully capable of outputting its rated CCA, depending on its SOH.

If the DC-DC is charging the engine and alternator connected to the house, then a house LFP disconnect *may* blow the alternator.

Not really. The DC-DC is limiting the current from start to LFP. The LA start battery acts as a buffer. This is a tried and true solution.

All of those problems are pretty well solved by an ACR, if only it was set for the right voltages (or a contactor turned on at the right times).

Not really. The ACR set point for opening/closing is immaterial to the pass through current. With the LA start battery in parallel with the LFP house battery via the ACR the alternator will be challenged to produce all of the current that the LFP house battery will accept.

The main point is to limit the amount of current being supplied by the alternator to keep its temperature below about 100C. An ACR will not serve this function.

As always, IYB.

 

[DDW]

@DDW

The starting battery, if the alternator has been running for more than about 5 minutes, is fully charged and is fully capable of outputting its rated CCA, depending on its SOH.

But of course you realize that the CCA spec allows very significant voltage sag (to 7.2V), right? The starter and thruster motor don't care (much), while the other electronics connected to it do not like that at all and will likely shut down. If this happens to be the engine ECU or electronic transmission controls, it is bad.

Not really. The DC-DC is limiting the current from start to LFP. The LA start battery acts as a buffer. This is a tried and true solution.

The part you quoted stated that the alternator was connected to the house and the DC-DC charging the engine. Unless you can guarantee that the transient response of the DC-DC is sufficient to absorb the energy spike in an LFP disconnect, your alternator may be toast.

What you say is true if the alternator is connected to the engine (as I said), but you are left with very limited house charge capability, unless many DC-DC are paralleled (which I also said).

Not really. The ACR set point for opening/closing is immaterial to the pass through current. With the LA start battery in parallel with the LFP house battery via the ACR the alternator will be challenged to produce all of the current that the LFP house battery will accept.

The main point is to limit the amount of current being supplied by the alternator to keep its temperature below about 100C. An ACR will not serve this function.

As always, IYB.

You entirely miss the point. If the ACR is properly closed there is current sharing for large loads, and an unlimited current path from alternator to house bank for both charge and discharge. Using a DC-DC to limit the current - and thus the alt temp - or expecting an ACR to do this is a very odd way to go about it. Any external alternator regulator worth considering measures alternator temperature directly and derates field current to keep alternator temperature under the set limit. That is the correct way to do it, and they do it very well.

 

[CharlieJ]

You entirely miss the point. If the ACR is properly closed there is current sharing for large loads, and an unlimited current path from alternator to house bank for both charge and discharge. Using a DC-DC to limit the current - and thus the alt temp - or expecting an ACR to do this is a very odd way to go about it.

I have missed no point. If the lashup is alternator > start battery > ACR > LFP house battery and the threshold is met so that the ACR is closed than the alternator is now feeding the LFP battery though the LA starting battery and the alternator is going to be challenged to put out as much as 100% of its capacity. It will damage the alternator.

or expecting an ACR to do this is a very odd way to go about it.

I don’t expect or advocate this at all and am dead set against it.

Any external alternator regulator worth considering measures alternator temperature directly and derates field current to keep alternator temperature under the set limit.

Of course this is the preferred method for charging the LFP house bank, The method that we have been discussing is for those installations where the owner doesn’t have an external regulator with an alternator temperature sensor in its feedback loop.

The internally regulated alternator > LA start battery > DC/DC converter > LFP house bank is tried and true with thousands of RV and marine installations.

The part you quoted stated that the alternator was connected to the house and the DC-DC charging the engine.

No I didn’t!! That is absolutely bass ackwards.
Here is my original post on the subject:

Most installers that are using an external alternator regulator to protect the alternator from the harsh demands of charging a LFP house bank use a DC/DC charger between the LA start battery and the LFP house bank. The “dumb” alternator charges the LA start battery and the DC/DC charger then is adjusted to limit the charge current allowed to flow to the LFP house battery. Typically the limit is set to keep the temperature of the alternator when going all out to be < 100C.

What you say is true if the alternator is connected to the engine (as I said), but you are left with very limited house charge capability, unless many DC-DC are paralleled (which I also said).

Of course!! The DC/DC charger is an alternate method to the optimized, and expensive, method of an upgraded HD alternator with an external regulator that includes an alternator temperature sensor in its feedback loop to reduce the charging current to keep the alternator temperature < 100C (I prefer <95C).

In this case the alternator’s output charges the LFP house bank and the start battery can be charged by the LFP bank through an ACR with the understanding that the start battery will not be charged underway with a LA algorithm.

As always, IYB.

 

[SteveK]

@DDW
I am beginning to think you will not understand @CharlieJ until you explain what "alternator is connected to the engine" means.
Usually the alternator is connected to the engine by bolts.

A properly sized DC2DC from the start FLA to LFP house will not hurt the ALT.
An ARC closed is then wide open freeway for all the current the ALT can provide and the LFP demand.

 

[tpbrady]

I think what DDW is getting to is the parts to do this the way he wants to do it and the way I would prefer to do it don’t exist yet. Both of us don’t see a problem charging the start and thruster batteries with the LFP charge profile. I chose to separate the battery banks for alternator charging using a battery isolator to feed the LFP and start bank and an ancient Xantrex Pathmaker to separate the thruster and LFP bank. I was able to set the Pathmaker to connect at 13.4v and disconnect at 13.2v. That kind of works as most DC loads on the LFP bank draw the voltage down below 13.2v so there is no parasitic draw. If it is above 13.2, I have a switch at the helm to manually shut it off or in emergency parallel it with the house bank.

My only problem is the Wakespeed regulator hates the Victron ArgoFET. So until I get the Balmar MC-618 set up, I am going the classic DC-DC charger way to charge the LFP bank. I have a dumb DC-DC charger with no float mode and learned don’t try to charge an LFP bank after being on shore power for a few days with a dumb charger because the batteries’ BMS terminated charging. Lesson: float the shore power charger at a voltage where SOC is less than 95% or so to leave the charger some head room to think it has to work. With that approach they haven’t shut down gain. I thank the ArgoFET for “protecting”the alternator.

Tom

 

[DDW]

We are discussing battery banks here. If you missed that, I will specify, when I say "alternator connected to house" I do not mean that the alternator is bolted to the roof.

I have missed no point. If the lashup is alternator > start battery > ACR > LFP house battery and the threshold is met so that the ACR is closed than the alternator is now feeding the LFP battery though the LA starting battery and the alternator is going to be challenged to put out as much as 100% of its capacity. It will damage the alternator.

I don’t expect or advocate this at all and am dead set against it.

Of course this is the preferred method for charging the LFP house bank, The method that we have been discussing is for those installations where the owner doesn’t have an external regulator with an alternator temperature sensor in its feedback loop.

The internally regulated alternator > LA start battery > DC/DC converter > LFP house bank is tried and true with thousands of RV and marine installations.

No I didn’t!! That is absolutely bass ackwards.
Here is my original post on the subject:


Of course!! The DC/DC charger is an alternate method to the optimized, and expensive, method of an upgraded HD alternator with an external regulator that includes an alternator temperature sensor in its feedback loop to reduce the charging current to keep the alternator temperature < 100C (I prefer <95C).

In this case the alternator’s output charges the LFP house bank and the start battery can be charged by the LFP bank through an ACR with the understanding that the start battery will not be charged underway with a LA algorithm.

As always, IYB.

From my post #15:

An externally regulated alternator is a given in this type of system. Doesn't really change any of the other issues.

An external regulator will control alt temp much better than throttling the charge to one or another bank and costs less than all the DC-DC chargers you will need otherwise.

From your post #16:

If the DC-DC is charging the engine and alternator connected to the house, then a house LFP disconnect *may* blow the alternator.

Not really. The DC-DC is limiting the current from start to LFP. The LA start battery acts as a buffer. This is a tried and true solution.

So yes, you did say that. We agree that connected the other way (alternator to engine BATTERY, and DC-DC charging house BATTERY) that there is little risk of alternator damage in a house BATTERY disconnect, however you are now severely limiting charge to the house which is defeating the whole point.

 

[DDW]

It appears that the Sterling VSR has sufficient adjustability of on and off voltages to accommodate LFP. On voltage as high as 13.9V, off as high as 13.5V, with a limitation that they must be at least 0.2V apart.

One possible problem is when the thruster draws a lot of current, will it be supplied mostly from the house battery, because of the flatter IV characteristic of the LFP house bank?

Tom, have you ever measured that? With combiner on and thruster on, current flowing from LFP house to AGM engine start? The alternator is also contributing with in theory an even flatter IV characteristic, at least up to its capacity.

The concern wouldn't be the energy loss from the house, which is negligible, but rather exceeding the capacity of the VSR.

 

[tpbrady]

The Pathmaker is rated at 200 amps and I haven’t seen it do anything unusual. The thruster I have is pretty anemic (5hp) so is only used on calm days for convenience and should draw around 300 amps. The windlass does not exceed the 200.

I have measured the parasitic draw between the LFP bank and thruster/windlass battery at about .5 amps when that battery is fully charged and the Pathmaker is connected. Not something to worry about.

Tom

 

[twistedtree]

Getting back to the VSR requirements to satisfy TPBrady’s needs, I don’t think voltage sensing, even if adjustable, will work reliably with LFP, simply because there is so little voltage swing in LFP across most of the SOC range, and very little change between charging, no current, and discharging. The voltage sensing depends on a reliably detectable difference in voltage when a bank is being charged, and that’s what turns on the VSR contactor. That’s easy to detect with lead, but I don’t think it can be done reliably with LFP.

So for a combiner relay to work, it needs to be triggered some other way, and a few have been mentioned, provided the device has some sort of trigger input. Ignition on would be a simple way, and probably work under most conditions. If I were building something like that, I would seriously consider installing an On/Off/Auto switch so that it’s controlled by the ignition in Auto, but can be manually overridden either Off or On, just to accommodate odd cases.

 

[NoRain]

Something like this? ML-ACR Heavy Duty Automatic Charging Relay 12V - Blue Sea Systems. I’ve got one, works very well. The ability to work as an emergency paralleling switch has come in handy more than once.

 

[CharlieJ]

@DDW

We are discussing battery banks here. If you missed that, I will specify, when I say "alternator connected to house" I do not mean that the alternator is bolted to the roof.

I will waste no more time with you.

 

[SteveK]

Something like this? ML-ACR Heavy Duty Automatic Charging Relay 12V - Blue Sea Systems. I’ve got one, works very well. The ability to work as an emergency paralleling switch has come in handy more than once.

That one still triggers at 13V so a 13.3-13.5v LFP will link the two banks. Or are you using it manually?

 

[DDW]

Getting back to the VSR requirements to satisfy TPBrady’s needs, I don’t think voltage sensing, even if adjustable, will work reliably with LFP, simply because there is so little voltage swing in LFP across most of the SOC range, and very little change between charging, no current, and discharging. The voltage sensing depends on a reliably detectable difference in voltage when a bank is being charged, and that’s what turns on the VSR contactor. That’s easy to detect with lead, but I don’t think it can be done reliably with LFP.

So for a combiner relay to work, it needs to be triggered some other way, and a few have been mentioned, provided the device has some sort of trigger input. Ignition on would be a simple way, and probably work under most conditions. If I were building something like that, I would seriously consider installing an On/Off/Auto switch so that it’s controlled by the ignition in Auto, but can be manually overridden either Off or On, just to accommodate odd cases.

I was sort of wondering if the turn on/turn off voltages could be tweaked to work, perhaps not.

On my current boat, Iv'e abandon the auto switching and it is forced on with ignition. I think in combination with a start lockout, it might work pretty well. The Blue Seas ACRs have a start lockout, so you can have it connect on ignition on, but disconnect on start solenoid active. That means a lot of switching unnecessarily: on with ignition, off and on again with each start attempt. So the refinement would be some delay relays: key on could be delayed 60 seconds say, then start circuit lockout delayed 30 seconds and re-triggerable. That would prevent combining during starting, and switch on only once per start cycle (usually anyway). Probably enough just to delay the ignition on by 60 seconds. The Blue Sea documentation suggests that their start lockout (isloation) input results in a 3-5 minute delay, but do not say how that interacts with the force on signal.

What is needed is for the Wakespeed to put out a signal indicating it is ramping up charge.

 

[twistedtree]

I was sort of wondering if the turn on/turn off voltages could be tweaked to work, perhaps not.

On my current boat, Iv'e abandon the auto switching and it is forced on with ignition. I think in combination with a start lockout, it might work pretty well. The Blue Seas ACRs have a start lockout, so you can have it connect on ignition on, but disconnect on start solenoid active. That means a lot of switching unnecessarily: on with ignition, off and on again with each start attempt. So the refinement would be some delay relays: key on could be delayed 60 seconds say, then start circuit lockout delayed 30 seconds and re-triggerable. That would prevent combining during starting, and switch on only once per start cycle (usually anyway). Probably enough just to delay the ignition on by 60 seconds. The Blue Sea documentation suggests that their start lockout (isloation) input results in a 3-5 minute delay, but do not say how that interacts with the force on signal.

What is needed is for the Wakespeed to put out a signal indicating it is ramping up charge.

You might be able to get it to work with adjustable voltages, but I suspect it will be very fragile. Pulling a signal from the Wakespeed is an interesting idea. Or any other source that will will give you a “running” indication. Maybe the Charge Lamp indicator?

 

[Insequent]

Something like this? ML-ACR Heavy Duty Automatic Charging Relay 12V - Blue Sea Systems. I’ve got one, works very well. The ability to work as an emergency paralleling switch has come in handy more than once.

Those are very good, but not appropriate for mixed LFP/AGM configurations. I used them while both house bank and start batteries were identical (Odyssey PC1800FT). After the LFP install (see post #4) I turned the one connecting house to start off, and labelled the house/start ACR "for emergency use" only.

With 2 x 200 A alternators, I have always connected alternators to house bank. Pointless to have that charging capacity connected to start batteries. So charging of the start batteries is via a couple of Victron DC-DC 30A chargers. With over 3 years of using the LFP's there have been no issues. I'm not sure how much current my JD 6068 TFM 75 (electronic) engines need when running, but the DC chargers keep up just fine.

For interest I have attached the charge testing done by the sparky after installing the LFP's. I did ask about alternator protection and his response was that in practice it was not necessary because the external VR (Balmar 612) and the battery BMS meant there would only low charge current just prior to batteries getting to the point at which the BMS might decide to disconnect. Disconnects may not even occur, the charge current might instead reduce to a "float" type low value. As I noted, more than 3 years and no issues. I can't help but wonder whether the "protect alternator" theories only apply to internally regulated alternators and/or DIY/cheap BMS's.