How to trickle charge starter battery from house battery set up?

[Superduty]

Also if you bought a dual dc to dc/mmpt they trickle charge the car battery of the solar once the house battery is full.

I have both the redarc and renogy and they both have this function.

Wonder why Victron's don't have that feature.

 

[Superduty]

Came across this a couple days ago. Seems relevant.

This looks to be the perfect solution for what I am trying to accomplish. Simple, effective and reasonably priced.

 

[Peter_n_Margaret]

Our crank and house are connected together via heavy cables and a relay. NOTHING ELSE.
If we are parked up for months I simply close the relay and the solar keeps everything charged.
Once on the road, the crank died and I started from the house for 3 months until we got home.
Don't over think it.
Cheers,
Peter
OKA196 motorhome

 

[dstefan]

Our crank and house are connected together via heavy cables and a relay. NOTHING ELSE.
If we are parked up for months I simply close the relay and the solar keeps everything charged.
Once on the road, the crank died and I started from the house for 3 months until we got home.
Don't over think it.
Cheers,
Peter
OKA196 motorhome

Makes sense if both house and crank are the same chemistry. The OP has LifePo house and FLA crank which isn’t a good mix directly connected.

 

[Peter_n_Margaret]

The OP has LifePo house and FLA crank which isn’t a good mix directly connected.

Why not? The voltages will be absolutely fine for both.
Cheers,
Peter

 

[dstefan]

I’m not the expert you need for the details, but in short, LifePo batteries have less resistance and take a charge faster. They can damage FLA batteries including AGMs if directly connected.

 

[Peter_n_Margaret]

I’m not the expert you need for the details, but in short, LifePo batteries have less resistance and take a charge faster. They can damage FLA batteries including AGMs if directly connected.

I don't think so. The LA will self protect. Just like connecting a 200A alternator to a LA battery. The voltage determines the rate of charge, not the alternator capacity.
Cheers,
Peter
OKA196 motorhome

 

[Superduty]

Other issues with having fla and lifepo4 connected together are that the lifepo4 voltage once all charged is higher than the fla. So i believe they will fight each other until they balance out, which won't be good.

Also can't start from the lifepo4. Way too many amps being sucked out too quickly.



Sent from my SM-G973U using Tapatalk

 

[Peter_n_Margaret]

Just don't tell those who are doing it.
Cheers,
Peter
OKA196 motorhome

 

[Beardy]

The manufacture of my Lithium battery does not recommend me connecting any other battery with it other than another identical one. They don’t even recommend a different size lithium of their own brand can be connected to it.
I know this because I wanted to increase my capacity and they were out of stock of my model and I had to wait

 

[dstock]

BCDC Classic 40A In-vehicle DC Battery Charger

The REDARC BCDC1240D is a 12V, 40A In-vehicle DC to DC Battery Charger designed to keep your auxiliary battery charged when driving or with portable solar panels when parked.

www.redarcelectronics.com

DCC50S 12V 50A DC-DC On-Board Battery Charger with MPPT

Make sure your service battery has all the juice it needs with Renogy's DCC50S DC-DC MPPT On-Board Battery Charger. 10% off: Renogy10off. Free shipping

www.renogy.com

There are multiple models with different amperage. I have used both and they both function well. Redarcs are about half the size of renogy but double the price.
I’m sure there are other company’s that make them as well.

Just a heads up, the Renogy has a solar input voltage limit of 25 volts. I recently upgraded from a 100 watt Renogy solar panel to a 160 watt Overland Solar panel and found this out the hard way. New panel output is 29-32 volts so I ended up swapping back to a Victron solar charge controller and a Victron DC-DC charger.

I do miss the starter battery being topped off like it was with the Renogy hence my interest in this thread as I too have an AGM starter battery and LifePo house battery.

 

[Joe917]

Although this might seem like a good idea, I think it's a bad one. Trickle charging a starter battery can disguise a battery not holding it's charge. When a battery goes bad it usually gives warning with slow cranks.

 

[waltermitty]

Although this might seem like a good idea, I think it's a bad one. Trickle charging a starter battery can disguise a battery not holding it's charge. When a battery goes bad it usually gives warning with slow cranks.

Which is why any charging should include follow up step of checking the internal resistance via load testing, specific gravity etc

 

[Trail Talk]

I've been contemplating the same issue as the OP since we changed our house batts from AGM to LiFePO4 and had to disconnect the Samlex ACR from topping up the truck batteries.

Removing shore power from the mix, there are couple of interesting devices that could do the job. I'd love some feedback on these:

OptiMate's DC-DUO 12V maintainer is a reasonable price but only provides 2A.



An all-in-one solution, but expensive, would be the new Sterling Power BB1240 DC to DC charger (or B to B as the Brits say) which is bidirectional, so operates like our Samlex did, and outputs 40A. Would replace our Victron Orion-Tr DC to DC.

 

[fratermus]

Any thoughts or suggestions on utilizing the house battery system to trickle charge the starting batteries if the truck sits for an extended period?

• dual-sensing VSR
• combo DC-DC with starter battery maintenance. To wit: Ctek, Renogy, SRNE, Rich Solar, Sterling BBS1230 Pro Batt Ultra. I'll believe the latter when I see it because Sterling docs have claimed that feature when it was not yet implemented in the device.

If the use case allows for self-jumpstarting (boost from aux batts if the starter batt runs down) we have more options.

Came across this a couple days ago. Seems relevant.

He is manually isolating when starting to avoid overcurrenting/smoking the PWM charger. This might be automated by by triggering a NC relay on the connection with the D+ signal.

Wonder why Victron's don't have that feature.

They are combo units (DC-DC + solar), and Victron does not offer that AFAIK.

Other issues with having fla and lifepo4 connected together are that the lifepo4 voltage once all charged is higher than the fla. So i believe they will fight each other until they balance out, which won't be good.

They aren't connected when not charging.

Also can't start from the lifepo4. Way too many amps being sucked out too quickly.

Thee is no rule that says one must connect then immediately crank. BMS limits can be respected by connecting, waiting a bit for them to equalize, disconnecting and cranking. I've done it.