Solar In The Desert

Ducky's Dad

Explorer
operating a battery in high temps requires temperature compensation. This means a remote temp sensor at the battery. Without temp compensation, the batteries life will be dramatically reduced.

My starting battery has a factory temp sensor built into the base of the battery box, and that battery is an Odyssey 2150 Extreme, 35 months old and won't take or hold a full charge. It is still fine for normal driving because the battery started out with so much excess capacity, but its reserve capacity is going away quickly. I think I'm going to try a Lifeline 31XT as a starting battery and a pair of G34 Odysseys or Northstars as house batteries. Nothing from Lifeline will fit the space for my house batteries, and Lifeline says their charge profiles are pretty close to Odyssey and Northstar.
 

luthj

Engineer In Residence
Curious, what is your alternator/charging voltage at these temps? At 120F cell temps it should be 14.0V or less if floating.
 

Ducky's Dad

Explorer
Alternator generally settles in at 13.6-13.9 at cruising speeds after truck has been on the road a while. At startup this morning, it touched 14.6 then quickly settled at 14.4 at idle. All three batteries are at low OCV.
 
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DiploStrat

Expedition Leader
Alternator generally settles in at 13.6-13.9 at cruising speeds after truck has been on the road a while. At startup this morning, it touched 14.6 then quickly settled at 14.4 at idle. All three batteries are at low OCV.

If you are getting performance like that, then you should probably go with a relay based system as a B2B isn't going to do anything but get you a slower charge. The D250SA is only going to get you a maximum of 20A; I suspect that your alternator will get you at least 100A, if your batteries need it.
 

Ducky's Dad

Explorer
If you are getting performance like that, then you should probably go with a relay based system as a B2B isn't going to do anything but get you a slower charge. The D250SA is only going to get you a maximum of 20A; I suspect that your alternator will get you at least 100A, if your batteries need it.
Well, yes, no, or maybe. I just don't know yet. The advantage of the D250SA is that it splits the solar charge between the starter battery and the house bank, plus it has a setting to charge at 14.7V for AGMs, so batteries should last longer with the trickle or better from solar when the truck is just sitting between trips. It is my understanding at this point that when the truck is running, the alternator can put its full amperage into the batteries (subject to what they need) and not be throttled by the Ctek, but the truck's ECU only goes up to 14.6V, not ideal for AGMs. So, theoretically, I can bulk charge from the alternator up to 14.6V and use the D250SA for the absorption charge at 14.7V and for the long tail that AGMs seem to like. If the D250SA won't pass the full alternator current to the batteries while I'm driving, then I can't use the D250SA.
 

dwh

Tail-End Charlie
That's IF you add the SmartPass to the 250s. Without the SmartPass you get the 20a of the 250, with SmartPass up to 80a.
 

Ducky's Dad

Explorer
Looks like I need to call Ctek again. If the D250SA chokes the alternator output down to 20 amps, I can't use it. May not have space for the Smart Pass and see no good reason to spend the extra money just to get 80 amps out of my 270 amp alternator.
 

DiploStrat

Expedition Leader
Looks like I need to call Ctek again. If the D250SA chokes the alternator output down to 20 amps, I can't use it. May not have space for the Smart Pass and see no good reason to spend the extra money just to get 80 amps out of my 270 amp alternator.

dwh and I read the CETEK documentation the same way. (See page 20: https://smartercharger.com/wp-content/uploads/2010/11/D250S-DUAL_EN.pdf) To get the full output (80A, limited by the wiring and size of the relay) of the alternator (without voltage boost) you need the SmartPass. The SmartPass opens and passes to the D250S when the amp flow drops to 20A. A clever best-of-both-worlds system

You may be much better off with a relay based system (I like intelligent relays) and a stand alone solar controller. This is what I had on my Chevrolet and it worked very well.

N.B. The Chevrolet ramped all the way up to 15.5v below freezing, it may be worth finding the manual for your truck to see what they claim. On some [most?] trucks the alternator has a built in 13.9v regulator that is then overridden by the vehicle computer(s). This allows the vehicle to keep the voltage up for things like headlights, air conditioners, and windshield wipers and drop it for highway cruising in cool weather. But the alternator/regulator/computer should always respond to low voltage at the starter battery. Or, as luthj suggested, the alternator output terminal.

Normally, as long as the wiring between your starter and camper (house) battery is large enough, the alternator will read this as a discharged starter battery and respond as needed. (OK, this is a gross oversimplification, but B2B/DC-DC/etc chargers work the same way, they drop the starter battery down to about 13v to make the alternator respond, then then they boost the voltage to whatever profile they have. Very clever, but not rocket science.
 
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john61ct

Adventurer
Yes CTEK 20A limit is not needed here.

Sterling not so limited, also fully adjustable.

B2B itself only needed if the voltage drop issue can't be overcome with fat wiring.
 

verdesard0g

Search and Rescue first responder
I live in the Verde Valley of AZ and often take my trailer south for a week at a time. I have 2 100w panels and 2 AGM batteries. the batteries and controller are mounted in the tongue box which is vented on two sides with louvers. The panels are on a long line so can be moved to follow the sun but in the desert I just aim them at the morning sun so to get the most power when it's cooler.
 

Ducky's Dad

Explorer
Here is one of the answers from Ctek re the D250SA, not good news:

I have answers to a few of your questions. Your 280A alternator will not damage the D250SA however the ambient temperature is going to be an issue. The charger will shut down in temps that exceed 122 F.

If it shuts down at 122F, then it's pretty useless after maybe 10:00am in the summer.
 

Ducky's Dad

Explorer
Here is the wiring diagram that Ctek sent me, reflecting my proposed setup. If I read this correctly, it looks like the D250SA will allow full charging from the alternator to the starting battery at up to 14.6V per the ECU (direct cable from alt to battery), but will send a max of 20 amps at 14.7V to the house bank while engine is running. When truck is parked, the solar panel will send current to the the D250SA which will then regulate the voltage to 14.7 (for AGMs) and send to starting battery and to the house bank, as needed by either battery. So, under this scenario, all batteries will get solar charge at 14.7V while parked, but house batteries will not have advantage of bulk charging directly from the alternator. Correct?

The down side of this setup is that I will have to disconnect the current positive cabling to the house batteries. Not wild about this idea.
 

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DiploStrat

Expedition Leader
Yep. And if your alternator/ECU is already putting out over 14v, then all you are doing is throttling your alternator down to 20A. That is why you must measure/monitor your vehicle's charging system for at least 30 minutes if you do not have a good tech manual.

Read this: https://cookfb.files.wordpress.com/2016/09/dual-battery-slides-2016.pdf

Were I thee, I would:

-- Pick my favorite intelligent relay. (I like the Blue Sea ACR range.)

-- Pick my favorite solar controller. (Don't have a current favorite here.)

Wire it up and be happy.

If you really must install a B2B, to help you sleep at night, then consider the REDARC BCDC 1240D. Like the CETEK it includes a solar controller but it has twice the output and is rated (reluctantly) for underwood mounting. (https://www.redarc.com.au/dual-input-40a-in-vehicle-dc-battery-charger) Or use one of the larger Sterling units and a stand alone solar controller. (But this may require more space than you have available.)
 

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