32 replies to this topic

[ckent323]

Vic,

 

Hah!  I have been asking myself the same thing: "are you over thinking this"?  

 

I have the house batteries instrumented with the Victron BVM-702 with bluetooth dongle and I will be installing a Bayrite volt/ammeter on the truck battery.

 

The ML-ACR would give me control, as you point out, and perhaps the most cost effective solution is the old school approach before the VSRs and ACRSs came on the market - pay attention and manually switch as required.  But don't forget to switch!

 

Your comments are appreciated!

 

;-)

 

Edit:  I just read your comment about overthinking this to Wendie, She immediately started laughing and said yup that sounds familiar!   

 

Hah!  We are all in agreement.  Must be closing in on the solution then. 

 

;-)

 

 

Craig

Edited by ckent323, 18 March 2018 - 03:44 PM.

[klahanie]

Craig, I dug up this charging test for your further reading. I think these are the Lifelines you have but in the 12V version which I have.

 

https://marinehowto....ery-be-charged/

[ckent323]

klahanie,

 

Thanks.  Yes, I have been looking a lot deeper into this.

 

Here is my current thinking (pun intended):

 

I can install a ML-ACR and periodically check my Victron BVM-702 battery manager.  Once the batteries move to absorption stage from bulk charging I would use the remote switch for the ML-ACR to disconnect the house batteries and just reply on the solar to finish the charging job. (Thanks to Vic for pointing this out).

 

The downside is that it is not automatic and idiot proof (I could forget to switch the house battery out of the charging circuit).  But it is one heck of a lot cheaper and less trouble than the battery to battery chargers I discussed above.  Further, it is not clear to me if the battery to battery chargers can support jumping the starter battery from the house batteries (still waiting for that question to be answered)

 

As for jump starting the truck diesel via the ML-ACR (or some other device) I got worried when looking at wire size charts and allowable current capacity of wires.  My starter can pull from 450 - 700 amps while cranking.  Even 4/0 wire is not rated for that amount of current

 

But then I realized the ratings are for steady state current.

 

So I found the following equation to calculate the wire size need for short term current.

 

S =( Ia.√t) / k

 

Where : S : Conductor cross section in mm2

Ia: Effective (rms/amount of DC current) value of current (A)

t: duration of hazardous shock current (sec.)

k: Cable Insulation Material Coefficient:

For PVC-insulated CU conductors : k=115 As/mm2

For PVC-insulated Al conductors : k=76 As/mm2

For rubber-insulated CU conductors : k=141 As/mm2-

 

Reference:  https://www.physicsf...-cables.330713/

 

Also I think that the truck battery will be not too far below the starter threshold current need of 450 amps when it is too low to crank the starter so I probably don't need more than 400 amps during jump starting (assuming the truck battery still has 200 - 300 amps or so available).

 

My truck usually starts with 3 - 4 seconds of cranking but when it is very cold it can take twice that long.  I did a calculation using 30 seconds and 400 amps assuming the CU PVC insulated wire and  that resulted in a wire cross section of 19 mm2.  4 ga wire has a cross section of 21.1 mm2

 

My conclusion is that 4 ga would work but 2 ga gives me some margin.  I like margin when designing things.

 

(now I understand why jumper cables which often only have 4 ga wire and are 20 feet long actually work)

 

P.S: for a non-diesel starter the current requirement is significantly less so my guess is that 4 ga and perhaps 6 ga might be adequate for gas engines.

 

 

I hope this is helpful to others following this as well.  Also if anyone sees any errors here please comment.

 

Craig

Edited by ckent323, 18 March 2018 - 08:10 PM.

[Vic Harder]

current thinking... LOL!  I've never met you or Wendie, but like you both more with every post!  

 

I like your refinement on my practice of manually switching = when the batteries move into absorb mode.  The Victron 7x2 series has provision for a relay function.... or is that in the MPPT?  (I'm traveling and don't have ready access to that info)  If we could use this relay to flip the ML-ACR that would help make the system more idiot proof.

 

To continue the puns... I think the idea has potential!

Edited by Vic Harder, 18 March 2018 - 11:12 PM.

[ckent323]

Vic,

 

Thanks.

 

I think you are thinking of the load output on the MPPT controller. The following is from the 75/15 manual section 4.3:

 

"For larger models without a load output, the load settings can be used to drive the TX pin in the VE.Direct port, which can then be used to drive a BatteryProtect relay or other load-shedding device. See chapter 4.4 Tx port function, option 5: Virtual Load output, for more information."

 

Hoping I don't have a "biased" perspective on this.  (OK, that one is a bit of a reach for a pun).

 

Craig

Edited by ckent323, 19 March 2018 - 02:32 AM.

[ckent323]

OK here is the latest on the Sterling Power BB1260 Battery to Battery Smart Charger (same as the Promariner ProNautic 1260P)I asked the following:

 

Can I reverse the charge and use this to jump start a low starting battery?

 

This is if the starting battery in the truck (FLA) runs down can I use the house batteries to jump start the truck battery with this unit.  Like I could do with an ACR or VSR?

 

To which the Sterling rep replied: We don’t have a setting like that, but if you had the ability to do that and tie input and output together for emergency start it wouldn’t harm the sterling dc to dc charger.

 

I also asked:

 

The BB1260 will accommodate both the FLA starting battery (that is being charged by the alternator/voltage regulator) and accommodate and properly charge the AGM house battery bank without the need for the battery chemistry module.

 

Please confirm.

 

Confirmed.

 

So the only advantage here over using a Blue Sea 7622 ML-ACR is that the battery to battery charger will not damage the AGM batteries if it is left to just work automatically.

 

However, since I have a solar system that will charge the house batteries (see discussion in earlier comment above) then as long as I monitor the house battery charging state while driving (using my Victron BVM-7x2 and the Victron App on my smart phone or ipad and manually switch the ML-ACR when the batteries change from bulk to absorption mode, the ML-ACR 7622 Will work fine and it is cheaper.  Further, the ML-ACR 7622 will allow me to flip a switch to jump the truck battery from the house batteries in the event I need to do that.

 

So I think this completes my research and decision making process.

 

Craig

Edited by ckent323, 20 March 2018 - 01:18 AM.

[ckent323]

Summary for those wanting to connect the house battery bank and the truck starting battery::

1. If you do not have a smart charging system in your vehicle then stick with normal capped lead acid batteries (flooded Lead Acid - FLA).
2. If you have or intend to install a smart battery charger in your vehicle then it may be appropriate to consider AGM or Gel (Gel for those driving a lot off road as they are less susceptible to damage from bouncing).
3. If the house batteries are the same chemistry as the vehicle starting battery there is no issue using an ML-ACR and I think it is a sensible thing to consider installing. You will need to bypass the typical OEM 110 V to 12 v charge controller (e.g. IOTA DLS-30) and connect directly to the house battery bank - there would be no need to use the factory pigtail plug in this case and the only use of the built in charge controller would be for converting 110 shore power to 12v.  This applies to the cases in 4 and 5 as well and the wiring is given in 6.
4. If the battery chemistry of the vehicle and house batteries are different then
   1. if you want automatic charging you will need to use a battery to battery (B2B) smart charger such as the Sterling Power BB1260 or the ProMariner 1260P.  However, you will not have flip a switch ability to jump start your vehicle battery from the camper battery and the current cost of the B2B snmart charges is close to 2x the cost of Blue Sea ML-ACR.  (there may be other products out there but after checking with Blue Sea, Balmer, Ctek, ProMarine, Sterling Power and Xantrex these are the only two products which I think will work (due to the potential of a >30 Amp current differential).
   2. if you are willing to monitor your house battery charging and accept the need to manually switch off the ACR but have the ability to jump the vehicle battery from the house battery bank with the flip of a switch then the ML-ACR is the way to go, BUT you must also have a solar system with smart charging to adequately charge the house battery bank (or plug the camper into shore power everyday).
5. For those who go on long trips or who want the security and piece of mind of knowing if you have good batteries and sufficient charge on the batteries ​I think it is important to be able to monitor the battery state of charge in both the vehicle and the camper.  There are a number of products that will allow you to do this.  The cheapest require running wiring to volt/ammeter in the truck cab and the more convenient Bluetooth equipped devices don't require running wire to the truck cab but cost more.  
6. If you want to be able to jump start your vehicle battery from your house battery bank I strongly recommend 4 ga wire for vehicles with gas engines and 2 ga wire for vehicles with diesel engines (see calculations for short term current capacity in an earlier comment above).

Unfortunately, at this time there does not appear to be a product on the market that will allow automatic smart charging of two different types of batteries in your vehicle and camper AND also allow a simple throw of the switch jump starting of a vehicle battery from the house battery bank.

 

I hope all this will be helpful to other folks.

 

Craig

Edited by ckent323, 20 March 2018 - 05:52 AM.

[Vic Harder]

Nice summary Craig

[philos65]

I'm confused by all the above.  Is there something wrong with using a voltage sensitive relay - something like this? 

 

https://www.amazon.c...duct/B0058SGDFK

 

Or am I missing something here - you want to do something other than use the alternator to charge both batteries, with priority being given to the truck battery, or use the auxiliary battery to help start the truck? 

 

Thanks for any clarity as to purpose of what seems to me to be a very complicated way to do something simple.  Or, I could just be showing my ignorance, which is pretty normal...

 

Jeff

[rando]

There is no problem using a VSR.   I would probably go with a bluesea SI-ACR for a few bucks more, as they are known reliable option:

https://www.amazon.c...keywords=si-acr

 

There is not really any 'priority' given.  The relay puts both batteries in parallel when either battery is charging, and isolates them when the charging stops. 

 

As usual, we have done an excellent job obfuscating the solution to a simple problem.