Tell me how please

[Arbee]

With the need to power two separate tasks: trickle charging two starter batteries and (re)charging a house battery that is constantly in use, operating a 4.2W 12V dash camera, including at night when that house battery is not being replenished by the sun, the notion of using two separate solar panels for each task, with their own controller, or one solar panel and system comes to bear for me.

It is my newbie understanding in a one solar panel setup that the solar panel and its controller will likely energize either the starter batteries (plural: I have two from the factory connected in parallel) or the house battery, and that the battery which is being replenished by the sun will then, vis a vis a DC to DC charger, charge the other battery system.

From what in my ignorance I can see, it seems that systems for sale for the most part charge the starter batteries, which in turn charge the house battery, vis a vis a DC to DC charger, but only when the engine is cranked, not my desired goal. I wish both battery systems to get replenished from the sun when the vehcile is parked.

How do I set this up? Which battery, the starter battery pair, or house battery best be direct connected to solar panel, and and what DC to DC charger might allow the other battery not directly connected via a charge contoller to the solar panel, to be replenished from the battery directly connected through a charge controlled to the solar panel?

Thank you.

 

[HarryN]

I am a big fan of the 26 x 59 inch or 26 x 62 inch range size of panels.

Especially for mobile applications they provide a very solid way to attach to vehicles easily. As a simple example, you can bolt them to 8020 frames such as 1515 or whatever is needed, or onto van / suv roof rails.

I don't see a need for a rack like that to mount your panels on top. Just bolt the panels directly to the round bars that are up there.

They are also very easy for 1 - 2 people to work with to mount them, vs larger panels might be cheaper per watt, but a paint to lift into place. I am in my 60s and can still lift a panel like that up onto a vehicle roof by myself, vs a 400 watt panel would be too large for me.

Multiple companies make them in the 150 - 200 watt range. Available in poly and mono, thinner frames or up to 2 inch deep frames for heavier duty use. Also available in nominal 18 volt Vmp or 36 volt Vmp, depending on what you project needs.

In my mind, 200 watts or less is for trickle charging a starter battery. It isn't until you get 400 + watts on top that it is doing any good for running devices regularly.

Agree about using AGM batteries for cold climates. Put in enough capacity for 2 - 3 days of operation. If solar is not enough, then add an alternator to battery pack charger in addition to solar.

If you build the system as a 24 volt setup, you can use a DC - DC converter, it is easier to support a more narrow voltage operating range, no matter what the battery pack is doing.

 

[robbob2112]

Lots of choices depending on your need. The other bit on LiFePO4 vs AGM - DOD can be as low as 1000% ... in reality you don't want to go below 80%. But that means a higher capacity in a smaller space and a LOT less weight.

So far all of LiTime's products are very good for budget options. So in this case budget doesn't mean cheaply made. And their return policy and tech support is really good.

https://www.litime.com/search?q=heated&options%5Bprefix%5D=last

 

[HRTKD]

Perhaps I should seek a small LiFePO4 with warming technology--as I am to understand that LiFePO4s can fit more "juice" in less space, much that I don't want to break the bank on this project.

Most of the LiFePO4 batteries with built-in warming, do not use the battery to power the warming system. Instead, the BMS diverts power from the charging source to the warming pads. With PV as your charge source, that charge current is only present when the sun is up. That means that during the night the battery temperature is going to fall, close to ambient temperatures. When the charge current is available, the warming system starts to bring the battery back up to an acceptable temperature. The battery is not charged until it reaches that acceptable temperature, which means you may miss out of valuable sun hours waiting for the battery to warm up.

 

[Arbee]

I am a big fan of the 26 x 59 inch or 26 x 62 inch range size of panels.

Especially for mobile applications they provide a very solid way to attach to vehicles easily. As a simple example, you can bolt them to 8020 frames such as 1515 or whatever is needed, or onto van / suv roof rails.

I don't see a need for a rack like that to mount your panels on top. Just bolt the panels directly to the round bars that are up there.

Thanks Harry. FWIW the roof rack panels on my vehicle also , by design, have many places in them to serve as attachment points as well https://www.lodoffroad.com/products/jk-jl-destroyer-roof-rack-aluminum-floor-kit-2-panels-per-kit-

They are also very easy for 1 - 2 people to work with to mount them, vs larger panels might be cheaper per watt, but a paint to lift into place. I am in my 60s and can still lift a panel like that up onto a vehicle roof by myself, vs a 400 watt panel would be too large for me.

Thanks, that's very relevant advise for me, your contemporary.

Multiple companies make them in the 150 - 200 watt range. Available in poly and mono, thinner frames or up to 2 inch deep frames for heavier duty use. Also available in nominal 18 volt Vmp or 36 volt Vmp, depending on what you project needs.

In my mind, 200 watts or less is for trickle charging a starter battery. It isn't until you get 400 + watts on top that it is doing any good for running devices regularly.

Okay, noted, but the sole devise I wish, and see myself ever needing to work regularly (in fact continually) only draws 4.2W at 12V.

Agree about using AGM batteries for cold climates. Put in enough capacity for 2 - 3 days of operation. If solar is not enough, then add an alternator to battery pack charger in addition to solar.

I hear you. But since I want to design this to work with my infrequent driving, AND my appliance (in addition to tricking charging the starter batteries) only pulls--again--4.2W @ 12V from the house battery, I was really hoping I could forgoe an alternator to battery pack charger.

I appreciate, where I running a home out of my vehicle, that some aspect of my desired design would have to "give." I'd have to tap shore power, cover my roof with solar panels, or crank the engine more and use an alternator to battery pack charger, etc.

If you build the system as a 24 volt setup, you can use a DC - DC converter, it is easier to support a more narrow voltage operating range, no matter what the battery pack is doing.

Thanks.

 

[Arbee]

Most of the LiFePO4 batteries with built-in warming, do not use the battery to power the warming system. Instead, the BMS diverts power from the charging source to the warming pads. With PV as your charge source, that charge current is only present when the sun is up. That means that during the night the battery temperature is going to fall, close to ambient temperatures. When the charge current is available, the warming system starts to bring the battery back up to an acceptable temperature. The battery is not charged until it reaches that acceptable temperature, which means you may miss out of valuable sun hours waiting for the battery to warm up.

Meaning that I'd have to--if taking the LiFePO4 battery warming route, account for this shortened time of sunlight actually charging versus warming the battery, through the introduction of greater power to the system, to wit, more solar, a bigger LiFePO4 battery, shore power, more engine on time, and/or an alternator to house battery charging mechanism.

Duly noted, thanks.

 

[HRTKD]

Meaning that I'd have to--if taking the LiFePO4 battery warming route, account for this shortened time of sunlight actually charging versus warming the battery, through the introduction of greater power to the system, to wit, more solar, a bigger LiFePO4 battery, shore power, more engine on time and an alternator to house battery charging mechanism,

More or less. The more insulation you provide around the battery, the less the warming system has to do and the quicker the battery can begin charging. More insulation means your available space may not be enough.

I have a DIY LiFePO4 battery bank with a custom warming system that keeps the batteries above 35°F all the time, so they're ready to take a charge as soon as the sun is up far enough for the PV to produce current.

 

[Arbee]

More or less. The more insulation you provide around the battery, the less the warming system has to do and the quicker the battery can begin charging. More insulation means your available space may not be enough.

I have a DIY LiFePO4 battery bank with a custom warming system that keeps the batteries above 35°F all the time, so they're ready to take a charge as soon as the sun is up far enough for the PV to produce current.

This warming system Jim, I presume, causing the battery bank itself to serve as its own warming agent rather than the solar panels in sunlight as you previously described in LiFePO4 warming batteries without a 3rd party custom warming system, correct?

 

[HRTKD]

Yes, the battery bank that is being warmed is the power source for the warming pads. With a good amount of insulation (to retain the heat) the pads don't draw down the battery much.

Here is my write-up of my warming system:

LiFePO4 Battery Warmer Install

This is my install of a custom set of battery warmers from Ultra Heat. I had contacted them through email asking about a warming profile for LiFePO4 batteries. They responded with a design to my specifications, including warming pads that fit my batteries exactly. While I initiated the...

diysolarforum.com

 

[Arbee]

Ok..so one solar panel or connected panels, and one charge controller...

which battery does it charge, the house battery or starter battery pair?

...and then what toys get me to charge the battery not directly connected to the charge controller even when the vehicle's engine is off?

Do I, for example, charge the starter batteries and then trick the DC to DC charger to think the engine is cranked so that starter battery pair charges the house battery?

Do I suck it up and use the Renogy DC30/50S given my low power needs and this Renogy appliance's ability, despite its limitations, to charge both batteries, house and starter?

Redarc, while not offering this dual house and starter battery capability does, given some work spelled out (and additional purchases) to me by a Redarc rep, does allow this dual house/starter battery charging functionality.

With my reasoning I fear spending enough money on tech to charge my dash camera that it will paradoxically justify the camera's existence in making the vehcile a desired targe to seize this very tech (lol)!

 

[Larry-Cleveland]

This is the DC to DC charger I am looking at for my slide-in truck camper build.

Factory web page

DMT1230/50​

When the motor is running it will charge the house battery from the vehicle battery system.

When the motor is off it will charge from solar. It will charge both house and vehicle batteries.

You can select battery types.

Good price

 

[Arbee]

This is the DC to DC charger I am looking at for my slide-in truck camper build.

Factory web page

DMT1230/50​

When the motor is running it will charge the house battery from the vehicle battery system.

When the motor is off it will charge from solar. It will charge both house and vehicle batteries.

You can select battery types.

Good price

Sounds close to perfect for my needs Larry. Thanks. I will carefully peruse the linked website.

 

[Arbee]

This is the DC to DC charger I am looking at for my slide-in truck camper build.

Factory web page

DMT1230/50​

When the motor is running it will charge the house battery from the vehicle battery system.

When the motor is off it will charge from solar. It will charge both house and vehicle batteries.

You can select battery types.

Good price

So I took a look. It's entirely possible that I am missing it Larry but I don't see where this device charges starter batteries, just house batteries or starter batteries from either a solar setup and/or the vehicle's alternator. Maybe I should say that I don't see where the device can concurrently charge from solar, both house and starter batteries.

I would love to be wrong here.

 

[Dave in AZ]

You don't need a "house" battery. You have one single small load. It's completely analygous to a standard normal car running a security system. All you need is a good starter battery, or 2 if you want more storage. You have zero "house needs". I have a house battery, but I have a doesel heater, LED lights, big maxxair fan, dc heated blankets, usb ports for laptops, a 12v water pump, a refrigerator...THOSE are house loads.

You have a wee normal security load. Stop making it more complex than needed, trickle charging one or other etc. Just wite camera to normal car system, then wire a solar panel to an mppt solar charge controller and connect it to your starter battery.

Just do the calculation like I did above, on how to balance the risk of a dead battery for YOU, depending on how much you drive car, which I never saw you say. By the way, how often you drive it is the #1 critical piece of info.

Don't want a dead battery? Then add more solar. Dont want or cant add more solar? Then add more battery to tide you through cloudy rainy periods. Done. There is no exact answer, you just decide on the balance of solar vs. Battery vs days cloudy vs days sitting undriven. I showed you the tools to make What If calcs and get your answer.

But seriously, all this talk of dcdc alternator chargers is just silly for your requirement. Pretend your car just has a parasitic draw like every modern car, that you have to solar trickle for.

 

[Arbee]

You don't need a "house" battery. You have one single small load. It's completely analygous to a standard normal car running a security system. All you need is a good starter battery, or 2 if you want more storage. You have zero "house needs". I have a house battery, but I have a doesel heater, LED lights, big maxxair fan, dc heated blankets, usb ports for laptops, a 12v water pump, a refrigerator...THOSE are house loads.

You have a wee normal security load. Stop making it more complex than needed, trickle charging one or other etc. Just wite camera to normal car system, then wire a solar panel to an mppt solar charge controller and connect it to your starter battery.

Just do the calculation like I did above, on how to balance the risk of a dead battery for YOU, depending on how much you drive car, which I never saw you say. By the way, how often you drive it is the #1 critical piece of info.

Don't want a dead battery? Then add more solar. Dont want or cant add more solar? Then add more battery to tide you through cloudy rainy periods. Done. There is no exact answer, you just decide on the balance of solar vs. Battery vs days cloudy vs days sitting undriven. I showed you the tools to make What If calcs and get your answer.

But seriously, all this talk of dcdc alternator chargers is just silly for your requirement. Pretend your car just has a parasitic draw like every modern car, that you have to solar trickle for.

I theorized the need for a separate dashcam running battery because all the solar in the world wont charge the starter batteries that you suggest I run my, granted, small power drawing dashcam
from at night.

Not the end of the world but the vehicle needs topped off starter batteries for the engine start stop to work.

I mentioned my once a week use of the vehicle but I’d reason should be battery irrelevant if the system you propose is keeping my starter batteries topped off from their losses to entropy and the dashcam combined, and yes gremlins in the electronics, no?

 

[Dave in AZ]

I theorized the need for a separate dashcam running battery because all the solar in the world wont charge the starter batteries that you suggest I run my, granted, small power drawing dashcam
from at night.

Not the end of the world but the vehicle needs topped off starter batteries for the engine start stop to work.

I mentioned my once a week use of the vehicle but I’d reason should be battery irrelevant if the system you propose is keeping my starter batteries topped off from their losses to entropy and the dashcam combined, and yes gremlins in the electronics, no?

I missed that once a week drive, that makes it tougher for a single battery. There definitely IS an mppt charge controller that has 2 dc outputs for 2 separate batteries, house and starter, and charges up house 1st then when full trickle charges both. This may be that renogy you mentioned above, I will look that up in a minute to see, I have so many product links saved...

Ok, I could swear I just read you said NY, but now can't find it. If so, daily solar in Dec in say Woodbury is 1350Wh, and thats the low for the year. But I'll keep using 1133 Wh a day to be conservative since I can't find where you said car is parked now.

So, 4.2W camera. To MAINTAIN a battery, not recharge, is just 1 to 2.5W on most battery maintainers. Say 2.5W. Let's assume your battery loses that much for some reason... I don't see why it would unless you have some parasitic drain, but conservative. Power needs are 6.7W. 24 hrs is 161 Whrs, or 12.5Amp hrs. I'm gonna use Ah as units even though it sucks, since car batteries are labeled that way and familiar.
If you want to be safe for 1 full week with no solar, you need 88Ah or 1126Wh (12.8v).

Why 1 week? Because you say you drive it weekly, and will be there in 7 days to start and charge car, clear snow from panels, etc. So, if it snows while you're gone, no solar, has to all come from a battery.

Most car batteries like group24 are 80Ah, of which 50% is usable, 40Ah. You can also actually start a car at 50% discharge. But I wouldn't want to risk that. Your setup only has 75Ah, of which maybe 40 usable.

How much more battery do you need? An AGM can use 80% of its charge, so for AGM which do well in cold you need 88Ah/80% is 110Ah. Thats a big battery. But Interstate has a 110Ah one for $309

https://www.amazon.com/Interstate-Batteries-DCM0100-SEALED-BATTERY/dp/B00YB26RYG

Or they have a 195Ah one for $340, better deal and solves problems but 117 lbs:

SRM-4D Deep Cycle Battery | Interstate Batteries

Play longer and harder with the SRM-4D deep cycle battery from Interstate Batteries. True deep cycling performance on land or water.

www.interstatebatteries.com

options:
1. start batteries in parallel. You already have a really weak setup, a 63Ah and a 12Ah battery, totalling 75Ah... less than my Honda in Phoenix. This isn't a good plan for a car left at 41N outside in the cold...
But I wouldnt add a 3rd battery to the mix. So,
2. A separate house battery to run camera. If a separate battery, then without solar the house needs 4.2w, 101Wh a day or just 55Ah in 7 days. A 200W panel in Dec gives you 226Wh a day or 17.6Ah. So it would take 3.12 average December days to recharge.

The start battery lets say drains 2.5W constantly, thats 33Ah in 7 days. Your 75Ah start combo can take that loss weekly and start ok, then you drive to recharge it and get your solar working.

Ok, looked it up. Yes the Renogy dcc30s or 50s are the ones that dual charge a start battery AND service battery, separately and isolates them. That unit does what you want. From the product info:

What will happen if the service battery is fully charged?​

This Renogy's DC to DC MPPT on-board Battery Charger has a built-in Voltage Sensitive Relay (VSR), thanks to which the charger will Trickle Charge the service battery and maintain its fully charged status, and will also Trickle Charge the starting battery via solar panels. The VSR also ensures reliable isolation between the starting battery and service battery, avoiding charging interference.

DCC30S 12V 30A Dual Input DC-DC On-Board Battery Charger with MPPT

Designed to give you options, the Renogy 30A Dual-Input DC-to-DC MPPT On-Board Battery Charger can charge a service battery in two different ways. The multi-stage charger can utilize connected solar panels or an alternator linked to a starting battery. While your vehicle's alternator prioritizes...

www.renogy.com

 

[Larry-Cleveland]

So I took a look. It's entirely possible that I am missing it Larry but I don't see where this device charges starter batteries, just house batteries or starter batteries from either a solar setup and/or the vehicle's alternator. Maybe I should say that I don't see where the device can concurrently charge from solar, both house and starter batteries.

I would love to be wrong here.

I did read it in the manual. Just send them an email. They have very good customer service.

But I do agree with Dave in AZ, you are building a very big mouse trap for a very small mouse.

I have a much bigger "house mouse" in my camper.

 

[Arbee]

I missed that once a week drive, that makes it tougher for a single battery. There definitely IS an mppt charge controller that has 2 dc outputs for 2 separate batteries, house and starter, and charges up house 1st then when full trickle charges both. This may be that renogy you mentioned above, I will look that up in a minute to see, I have so many product links saved...

Ok, I could swear I just read you said NY, but now can't find it. If so, daily solar in Dec in say Woodbury is 1350Wh, and thats the low for the year. But I'll keep using 1133 Wh a day to be conservative since I can't find where you said car is parked now.

So, 4.2W camera. To MAINTAIN a battery, not recharge, is just 1 to 2.5W on most battery maintainers. Say 2.5W. Let's assume your battery loses that much for some reason... I don't see why it would unless you have some parasitic drain, but conservative. Power needs are 6.7W. 24 hrs is 161 Whrs, or 12.5Amp hrs. I'm gonna use Ah as units even though it sucks, since car batteries are labeled that way and familiar.
If you want to be safe for 1 full week with no solar, you need 88Ah or 1126Wh (12.8v).

Why 1 week? Because you say you drive it weekly, and will be there in 7 days to start and charge car, clear snow from panels, etc. So, if it snows while you're gone, no solar, has to all come from a battery.

Most car batteries like group24 are 80Ah, of which 50% is usable, 40Ah. You can also actually start a car at 50% discharge. But I wouldn't want to risk that. Your setup only has 75Ah, of which maybe 40 usable.

How much more battery do you need? An AGM can use 80% of its charge, so for AGM which do well in cold you need 88Ah/80% is 110Ah. Thats a big battery. But Interstate has a 110Ah one for $309

https://www.amazon.com/Interstate-Batteries-DCM0100-SEALED-BATTERY/dp/B00YB26RYG

Or they have a 195Ah one for $340, better deal and solves problems but 117 lbs:

SRM-4D Deep Cycle Battery | Interstate Batteries

Play longer and harder with the SRM-4D deep cycle battery from Interstate Batteries. True deep cycling performance on land or water.

www.interstatebatteries.com

options:
1. start batteries in parallel. You already have a really weak setup, a 63Ah and a 12Ah battery, totalling 75Ah... less than my Honda in Phoenix. This isn't a good plan for a car left at 41N outside in the cold...
But I wouldnt add a 3rd battery to the mix. So,
2. A separate house battery to run camera. If a separate battery, then without solar the house needs 4.2w, 101Wh a day or just 55Ah in 7 days. A 200W panel in Dec gives you 226Wh a day or 17.6Ah. So it would take 3.12 average December days to recharge.

The start battery lets say drains 2.5W constantly, thats 33Ah in 7 days. Your 75Ah start combo can take that loss weekly and start ok, then you drive to recharge it and get your solar working.

Ok, looked it up. Yes the Renogy dcc30s or 50s are the ones that dual charge a start battery AND service battery, separately and isolates them. That unit does what you want. From the product info:

What will happen if the service battery is fully charged?​

This Renogy's DC to DC MPPT on-board Battery Charger has a built-in Voltage Sensitive Relay (VSR), thanks to which the charger will Trickle Charge the service battery and maintain its fully charged status, and will also Trickle Charge the starting battery via solar panels. The VSR also ensures reliable isolation between the starting battery and service battery, avoiding charging interference.

DCC30S 12V 30A Dual Input DC-DC On-Board Battery Charger with MPPT

Designed to give you options, the Renogy 30A Dual-Input DC-to-DC MPPT On-Board Battery Charger can charge a service battery in two different ways. The multi-stage charger can utilize connected solar panels or an alternator linked to a starting battery. While your vehicle's alternator prioritizes...

www.renogy.com

Thanks again Dave for taking the time to do the math here and spell things out.

 

[Arbee]

I did read it in the manual. Just send them an email. They have very good customer service.

But I do agree with Dave in AZ, you are building a very big mouse trap for a very small mouse.

I have a much bigger "house mouse" in my camper.

The thing of it is Larry is that I'm not really building anything yet. I started with a problem and in my limited knowledge proposed a solution for others to critique or elaborate on.

And you have critiqued it, quite possibly accurately, as an approach that best is scaled down.

Thanks for your time and thoughts.

 

[Browneye]

Dear lord…

Anyway…I have a similar system that keeps motorhome starting batteries topped off and ready to go with a 100W panel and controller on two engine starting batteries for a 8.1L gas V8. It could easily power a dash cam.

I like the black frame panels, and renogy makes a super cheap charge controller for lead acid, all in maybe a couple a hundred, and it works just killer.

In hindsight, with a larger lifepo4 house battery I would likely choose a trickle start or similar and forego the solar panel for the starting batteries.