12 replies to this topic

[steve whiteside]

Gents, as some of you know Im trying to track down a battery drain in my 2020 Granby FWC.

 

I see a 7w continuous drain that Ive tracked to the charging relay.  I can pull the fuse and it goes away.  I put the fuse back in and after a minute or two it pops back on- pulling 14watts that quickly degrades down to 7w continuous.  

 

Does anyone know the function of this and why it would actuate?  The camper was not plugged in to shore power.  Realize that I have  solar panels that are disconnected by fuse block.  I'm also running the Victron solar charge controller (on with blue bulk light blinking) and Victron battery manager also "on" via the shunt.

 

steve

[ckent323]

Steve Whiteside,

Some questions to aid in understanding the setup:

Is the ACR near the truck battery? 

Is the ACR between the truck battery and the camper battery bank? 

What is the size of the wire connecting the ACR to the battery in the truck and to the camper?

Are the truck battery and the camper battery bank the same battery chemistry (Both AGM)?



Craig

[steve whiteside]

I did not know it was that involved!  Thanks for the reply though.  Is the ACR the DC to DC converter that provides DC form the truck battery to the camper battery?

 

The ACR is not very near the truck battery.  It is buried in the Camper.  Probably 20' of wire to get from the batteries in the truck to the ACR in the camper.  Then 2-3ft to get to the camper batteries.  The camper is connected via pretty small wires in the FWC wiring harness.  

 

Im not sure exactly how the ACR is wired.  It came with the camper and it is how ever they wired it.  

 

I can check on the wire size but i heard that the FWC current pulled from the truck when driving is not much.  So, Im guessing small wires.  

 

I have AGM in the truck and Li in the camper.  The camper came with AGM but I swapped them for Li.

 

steve

Steve Whiteside,

Some questions to aid in understanding the setup:

Is the ACR near the truck battery? 

Is the ACR between the truck battery and the camper battery bank? 

What is the size of the wire connecting the ACR to the battery in the truck and to the camper?

Are the truck battery and the camper battery bank the same battery chemistry (Both AGM)?



Craig

[ckent323]

You wrote:  <I have AGM in the truck and Li in the camper.>

1) AGM and LiFePO4 batteries have different chemistries and different charging needs.

2) The AGM battery wants about 13.8 v to 14.4 v during bulk/absorption charging phases dropping to about 13.5 v for float (maintenance charging)

3) Lead acid batteries will degrade if chronically overcharged or undercharged so always fully recharge before discharging again as well as avoid routinely discharging below about 50% SOC (50 % of full charge).

https://batteryunive...rging-lead-acid

 

4) The LiFePO4 battery wants 14.4 to 14.6 Volts during bulk charging
5) The LiFePO4 battery wants around 13.5 V float voltage (many adjust this lower - see below)
6) However, Li-ion does not need to be fully charged as is the case with lead acid, nor is it desirable to do so. In fact, it is better not to fully charge because a high voltage stresses the battery. Choosing a lower voltage threshold or eliminating the saturation charge altogether, prolongs battery life but this reduces the runtime. 

7) A lithium battery charger will damage a lead acid battery by overcharging it with high voltage

 

https://batteryunive...ing-lithium-ion

 

 

All that written the key may be where the ACR is installed and perhaps the size of the wires (if they are too small min of 6 ga is recommended)  It should be in the truck close to the AGM starting battery.  Also that assumes your truck does not have a smart charger.

It seems that the ACR is not protecting the AGM battery for some reason (not switching off) and what is happening is that your charge controller is trying to bring the whole system up to the voltage set for charging the Lithium battery bank (is your charger programmable?).  If that is true you are constantly overcharging your truck battery. Another possibility is that there is something in the truck constantly putting a small load on your truck battery (an accessory or bad connection or something).

But I am confused because you seem to imply by your comments that you also have a DC to DC charger.  If that is true I am pretty sure you do not need an ACR. It would be helpful if you could describe the system a little better. A diagram would help.

By the way both ends of the wire between the truck battery and the camper battery (which I recommend should be at least 6ga) should have a large fuse 120 Amps or more.  Blue Sea resettable fuses are reasonable.

I do not have hands on experience with DC - DC chargers and smart alternators. Ntsqd or Vic or Rando, if he is still around, may have better insight so hopefully one or more of them will weigh in.  

I hope this is helpful and not too confusing

Craig


 

Edited by ckent323, 29 October 2022 - 09:01 PM.

[Jon R]

The Blue Sea ACR disconnect voltage is about 12.75 volts. A LiFePO battery at about 50% charge or above will hold the ACR-sensed voltage higher than that (assuming the truck battery is near full charge) and prevent ACR disconnection, even if the truck engine is shut down, until the voltage at the ACR drops to 12.75.

Edited by Jon R, 30 October 2022 - 12:08 AM.

[steve whiteside]

So, good info above from craig, thanks.  FYI I have not installed a DC to DC converter.  A wirnging diagram from the factory would be very handy as well as a diagram showing the location of all of the parts.  

 

Jon, Im trying to understand your comments.  So is the function of the ACR to take voltage from the truck and provide that to camper batteries- when truck is running?  The Blue Sea will disconnect when it senses the INCOMING AGM voltage at less than 12.75 volts??  The truck turns off, the voltage drops, the ACR relay turns off??  Is that what is supposed to happen?

 

Remember the Li batteries are in the camper not the truck.  

 

One piece of perhaps useful knowledge is I JUST put two new AGM batteries in the truck.  They were stamped with last month and I bought them at costco.  I installed them 2 days ago, fired the truck to make sure it ran and since then -no driving or no electrical loads.  I just went down to the truck and measured the new AGM's in the truck.  12.77v on both.  

 

Armed with the comments above from Jon and Craig I wonder if since new batteries on truck are at an artificially high voltage the ACR senses the incoming volts and turns on BUT uses the camper batteries to hold the relay shut??  Slowly draining my camper batteries but not touching the truck batteries.  

 

Thoughts?

 

steve

[ckent323]

Steve,

 

Look up Blue Sea ACR operation here:

https://www.bluesea....[ACR]_Explained

 

I found this:

https://www.bluesea....these programs.

 

If two battery banks, with different chemistries are connected together through an ACR, then two charging profiles are applied to each battery bank. An ACR that combines battery banks under these circumstances may interfere with the charging performance, and reduce any benefit from running these programs.

 The charging profile that is ideal for one battery chemistry may be too aggressive and therefore harmful to another.  This is especially a problem when different battery types are used in the system, such as a conventional flooded cell starting battery and an AGM or Gel deep cycle house battery bank (or AGM and Lithium). The solution is to prevent the ACR from connecting the batteries when the shore or solar charger is active.

This Blue Sea ACR has a lock out switch and is what I use in my system:

https://www.bluesea....l_-_12V_DC_500A

 

 

[Jon R]

So, good info above from craig, thanks. FYI I have not installed a DC to DC converter. A wirnging diagram from the factory would be very handy as well as a diagram showing the location of all of the parts.

Jon, Im trying to understand your comments. So is the function of the ACR to take voltage from the truck and provide that to camper batteries- when truck is running? The Blue Sea will disconnect when it senses the INCOMING AGM voltage at less than 12.75 volts?? The truck turns off, the voltage drops, the ACR relay turns off?? Is that what is supposed to happen?

Remember the Li batteries are in the camper not the truck.

One piece of perhaps useful knowledge is I JUST put two new AGM batteries in the truck. They were stamped with last month and I bought them at costco. I installed them 2 days ago, fired the truck to make sure it ran and since then -no driving or no electrical loads. I just went down to the truck and measured the new AGM's in the truck. 12.77v on both.

Armed with the comments above from Jon and Craig I wonder if since new batteries on truck are at an artificially high voltage the ACR senses the incoming volts and turns on BUT uses the camper batteries to hold the relay shut?? Slowly draining my camper batteries but not touching the truck batteries.

Thoughts?

steve

I was going to post the same link that ckent323 posted (the first one). It explains the ACR function.

Note that the Blue Sea ACR does not sense one or the other battery connection voltage as “incoming.” It will close the relay when either battery voltage exceeds the connect voltage of about 13.0 Volts. It will open the relay when the voltage of the connected batteries at the ACR falls below 12.75 Volts. As you can imagine, there are scenarios with one battery charged (or assisted by an alternator) and the other discharged where the ACR will cycle on and off.

Regarding your last thought, if the agm batteries in the truck are fully charged (around 12.8 Volts when relaxed), and your lithium battery is fully charged (around 13.4 Volts), then that voltage difference and the greater wire resistance of the wires coming from the truck battery will cause nearly all of the ACR operating current to come from the camper battery. Your camper battery is also supplying some current to the truck battery in that condition.

Edited by Jon R, 30 October 2022 - 02:28 AM.

[steve whiteside]

Steve,

 

Look up Blue Sea ACR operation here:

https://www.bluesea....[ACR]_Explained

 

I found this:

https://www.bluesea....these programs.

 

If two battery banks, with different chemistries are connected together through an ACR, then two charging profiles are applied to each battery bank. An ACR that combines battery banks under these circumstances may interfere with the charging performance, and reduce any benefit from running these programs.

 The charging profile that is ideal for one battery chemistry may be too aggressive and therefore harmful to another.  This is especially a problem when different battery types are used in the system, such as a conventional flooded cell starting battery and an AGM or Gel deep cycle house battery bank (or AGM and Lithium). The solution is to prevent the ACR from connecting the batteries when the shore or solar charger is active.

This Blue Sea ACR has a lock out switch and is what I use in my system:

https://www.bluesea....l_-_12V_DC_500A

 

 

Craig, Great links, thanks.  I need to read up on this a bit more later today.  It seems like the ACR with lockout is a good way to go.

 

steve

[Vic Harder]

The ML-7622 ACR has a lockout. When mixing Li and Lead acid, the higher resting voltage of the lithium battery will keep the ACR connected and drain the camper battery until the voltage drops enough.

not good if you want to keep your camper batteries at max charge, great if you want to trickle charge your truck batteries.