How to maintain the Starting Batteries off of Lifep04 House batteries.

[ckent]

I currently don't have a way to keep my starting batteries charged while my rig is sitting. I have plenty of solar and battery capacity, but I haven't figure out how to transfer energy from my battery pack or solar to my starting batteries, since the house system is set up to handle the lithium pack.

Currently, my best idea is to install a Victron Orion 12v 9amp DC-DC charger and set the output voltage to 13.4v. Then control it via one of the additional outputs of my SBMS0 so it's only active when my house pack is at a set SOC, maybe 85-90%.

But I don't know much about lead acid batteries. Will always holding them at a set voltage hurt them? And will the Victron unit get damaged when I start the truck and the chassis side is sitting at 14.6 volts from the alternators?

I've included a simple schematic showing the major layout of my electrical system for reference.




Edit: Increased size of schematic.

 

[ckent]

I'm not sure why the quality is so poor, here's a link to the full-quality image.

Electrical Schematic.

 

[MisterSandals]

I have a Trickl Start from my house batteries to the engine battery of my Sprinter RV. The house batteries were lead acid and for the last year+ LiFePO4. This trickle charger made my engine battery last 9.5 years with zero maintenance or effort.

My house batteries are kept charged with solar.

Mega TRIK-L-START Starting Battery Charger/Maintainer

Automatic Battery Charger/Maintainer for Motorhomes

www.lslproducts.net

I have the original version that I believe was 2 amps. Its been working, tucked away and out of sight since early 2011.

 

[richard cabesa]

Amp-L-Start is what I use. Uses a few watts for a few hours a few times per week.
I actually hooked mine to the Load side of one of my charge controllers.
it only takes juice if the sun is shining and my expensive AGM chassis battery is always happy now
It is really insignificant and unnoticed draw from the house

 

[ckent]

I have a Trickl Start from my house batteries to the engine battery of my Sprinter RV. The house batteries were lead acid and for the last year+ LiFePO4. This trickle charger made my engine battery last 9.5 years with zero maintenance or effort.

My house batteries are kept charged with solar.

Mega TRIK-L-START Starting Battery Charger/Maintainer

Automatic Battery Charger/Maintainer for Motorhomes

www.lslproducts.net

I have the original version that I believe was 2 amps. Its been working, tucked away and out of sight since early 2011.

Thanks! I saw your comments about this in another thread, and was already considering it.

Amp-L-Start is what I use. Uses a few watts for a few hours a few times per week.
I actually hooked mine to the Load side of one of my charge controllers.
it only takes juice if the sun is shining and my expensive AGM chassis battery is always happy now
It is really insignificant and unnoticed draw from the house

I reviewed both the Amp-L-Start and the Victron Orion controlled by my BMS, and decided to go with the AMP-L-Start. While it would be nice for the charger to be controlled directly by my BMS, it'll still pull power from the switched side of my Battery Protect. The AMP seems to have a better charging profile for starting batteries, rather than just applying a fixed voltage like the Orion would, and the install will be easier without having to run signal wires from my bms to the Maintainer.

 

[John Frum]

Diagram even at full resolution is too small for my eyes but I think I see a victron battery protect between the inverter and the battery.
Possibly between the inverter and a charge source.
Both of those things are can melt the battery protect.

 

[mikefitz]

For a 12v system connect a 21w 12v bulb and Schottky diode in series between the house battery and starter battery with a 5A fuse at each battery. This will provide a current limited maintaining charge to the starter battery.


Mike

 

[GSXR1000]

 

[ckent]

Diagram even at full resolution is too small for my eyes but I think I see a victron battery protect between the inverter and the battery.
Possibly between the inverter and a charge source.
Both of those things are can melt the battery protect.

I replied to the first post with a link to a full-resolution image. The battery protect is between the battery and load sources only. The dc-dc charger, solar, and inverter/charger all connect to the common positive between the battery protect and battery.

For a 12v system connect a 21w 12v bulb and Schottky diode in series between the house battery and starter battery with a 5A fuse at each battery. This will provide a current limited maintaining charge to the starter battery.
View attachment 45843

Mike

That’s an interesting solution, but I already ordered the AMP-L-Start, so I’m going to give that a whirl.

View attachment 45879View attachment 45880

The remote functionality is what made me think this would work, as it could be controlled directly by my BMS. However, it only outputs a set voltage, whereas the AMP-L-Start has a little more intelligence in its charging, at least from their brochure. Also, once I bump the Orion up to match the 15 amp capacity of the AMP it surpasses it in price. So I’ll give the AMP a try and see how it works.

 

[TheDude]

For a 12v system connect a 21w 12v bulb and Schottky diode in series between the house battery and starter battery with a 5A fuse at each battery. This will provide a current limited maintaining charge to the starter battery.
View attachment 45843

Mike

How would one accomplish the same but with a higher than 5A current limit?

 

[MattiFin]

How would one accomplish the same but with a higher than 5A current limit?

21W light bulb limits the charge current to less than 0.5A on 12v-12v system unless starter battery is totally dead sitting at 0volts.

If you want to create something similar with shoestring budget use H4 lightbulb low&high beam connected together making it 2x55=110w bulb. This will limit the current to max 9Amps or so. (Use also bigger fuses and diode). Again the charge current is going to be fraction of maximum unless your starter battery is totally flat)

 

[Browneye]

I spent about $140 for a 100w solar panel and a 10A pwm controller. Keeps the starting batteries topped up.
This before I was aware of the ampl-start and trikl-start thingies.

 

[TedH]

I currently don't have a way to keep my starting batteries charged while my rig is sitting. I have plenty of solar and battery capacity, but I haven't figure out how to transfer energy from my battery pack or solar to my starting batteries, since the house system is set up to handle the lithium pack.

Currently, my best idea is to install a Victron Orion 12v 9amp DC-DC charger and set the output voltage to 13.4v. Then control it via one of the additional outputs of my SBMS0 so it's only active when my house pack is at a set SOC, maybe 85-90%.

But I don't know much about lead acid batteries. Will always holding them at a set voltage hurt them? And will the Victron unit get damaged when I start the truck and the chassis side is sitting at 14.6 volts from the alternators?

I've included a simple schematic showing the major layout of my electrical system for reference.


View attachment 45584

Edit: Increased size of schematic.

I run a Pulsetech Xtreme battery maintainer (12v x 2) off via an AC outlet powered from the breaker panel that I feed with AC power from the inverter that is fed by the solar charging system/shore power.

 

[Vigo]

I think the simple solution here is to get a super cheap pwm SCC, hook it to the unswitched 12v lead acid circuitry somewhere (doesn't have to be the battery, really), and use the lifepo4 as the input. The pwm controllers don't need a minimum voltage input, just has to be higher than the lead voltage to work. Doesn't have to hook directly to battery, just has to hook up to an unswitched 12v circuit that can handle the current you're going to put to it. You would then have to implement some form of your own current control like the lightbulb thing.

Like this: https://www.amazon.com/gp/product/B08H24CMW1/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

It has an adjustable current limit, and it works (i own one). It's accurate within about 1-2amps of what my clamp meter says. So its 'power tracking' feature will not be super accurate since its amps counter isn't either, but it WILL limit current anywhere from 1-20a in 1a increments. Which means you could basically hook it to ANY unswitched 12v circuit leading back to battery, and then adjust current limit to suit the 'overhead' of that circuit.

I'm saying it doesn't have to hook directly to lead battery because logistically it might be annoying to run wire all the way between the lithium and lead batt locations.

In my RV I have large battery cabling which runs from starter battery to the original lead house battery going right next to my lithium batteries. I could easily tap into them to charge start battery from, lithium.

I currently am working on a lithium to lead passive trickle charge using a diode such as mikefitz mentioned above, but mostly as an experiment to see how well i can make it work. I already have this 20a adjustable controller sitting unused (recently freed it up) and if i wanted the easy button i would just hook it directly between the lithium and lead banks and be done.

This does require the lithium to not be chassis grounded as most pwm scc's have all the positive terminals bridged together. If both batteries are chassis grounded the pwm scc would just short them together on positive.

 

[Goboatingnow]

To charge smaller batteries from Li I use 6A buck boost dc dc converters from AliExpress $5 ( available from Amazon sellers and EBay too ) these converters have CV and CC limits.

Very useful also where you need a 12v specific voltage.

 

[Vigo]

Do you know of any specific order of hookup or 'gotchas' on those small converters? I ordered one from Amazon and had it working but i think i killed it with incidental contact between something briefly shorting it, which killed it. But i can't remember what i did and without the knowledge of how exactly to avoid repeating it, or what specifically will kill them, i have not ordered another..

I do understand it was my fault..?

 

[Goboatingnow]

Do you know of any specific order of hookup or 'gotchas' on those small converters? I ordered one from Amazon and had it working but i think i killed it with incidental contact between something briefly shorting it, which killed it. But i can't remember what i did and without the knowledge of how exactly to avoid repeating it, or what specifically will kill them, i have not ordered another..

I do understand it was my fault..?

Sometimes full short circuit protection isn’t available on these cheap units. They can’t handle the heat , a fuse is needed

Secondly if charging a battery put a diode in series ( and that fuse ) with the positive output from dc dc unit. Many don’t have that diode and back feeding from the battery kills them ( some do have diodes )

Thirdly if you push the ratings you’ll need to add a fan.

Other that that all mine survived my recent lightening strike , all the Victron stuff died.

 

[Vigo]

Oh, i thought i was doing well for a minute.. I put it in the gutted case of a broken meanwell knockoff power supply, with thermal transfer tape between the bottom and the case.. with the fins oriented in the direction the case fan would be pulling the air across it. Basically a 'shrouded fan'/heat sink setup using the old power supply case. Then i fried it!

Oh well, may try again sometime. Thanks for the reply!

 

[Goboatingnow]

Oh, i thought i was doing well for a minute.. I put it in the gutted case of a broken meanwell knockoff power supply, with thermal transfer tape between the bottom and the case.. with the fins oriented in the direction the case fan would be pulling the air across it. Basically a 'shrouded fan'/heat sink setup using the old power supply case. Then i fried it!

Oh well, may try again sometime. Thanks for the reply!

Shorting it will do that !