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"Lot Rot" & Solar Trickle Charger


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#1 Jack

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Posted 20 May 2020 - 09:18 PM

Today's vehicles have a lot of accessories and features that draw a small amount of current when the engine is off. If a vehicle sits on a dealer's lot for too long, the battery runs down. Car dealers call it "lot rot".

 

If you have a recent vintage truck and it's parked for a few weeks, you need to deal with lot rot. It's not a problem with the camper battery if you have solar (and light) or if you remember to pull the switch and disconnect the battery.

 

I found out the hard way. With the stay home edict of the pandemic, we have not been able to get out of Dodge (aka Portland) since late January. A few weeks ago, I went to start the Ford Ranger and the battery was dead - 5.5V. I got it jump started and then began testing the current draw when the engine was off. I had a lot to learn. The current draw can be almost 0.5A right after opening the door. It now makes sense as the locks open, cabin lights come, and various device power up in anticipation of startup. Not realizing this, I called the Ford dealer and they had me bring it in - 500 mA was out of spec. They tested the battery and the current draw and said all was well. The maximum spec for the Ranger was 50 mA with the engine off for 10 minutes. Mine drew 36 mA after the engine was off for a while. They tested the battery and said it was good.

 

This still didn't sit right, so I did further testing. Because it takes several hours, I'm sure they did not do a capacity test, which is quite different than testing the starting capability of a battery. My less than year-old battery is rated for 70 Ah new, and when I tested it, it was down to about 30 Ah. Since the truck draws a bit less than 1 A/day (24 x 0.036 A), the battery will be 75% discharged in about 3 weeks.

 

Completely discharging the battery did the damage. Ford does not warn you about lot rot, although they do say in the manual that if the vehicle will be idle for more than 30 days to disconnect the battery ground.

 

The simple solution is to start the truck every few weeks and let it run for 30 minutes or so. Or, if you have 120V handy, put a decent trickle charger on the battery.

 

Since where I park does not have 120 V, I’ve gone with a solar trickle charger.

 

Big Caveat! If you get a “solar trickle charger” make sure it has a charge controller built in or you add it externally. Amazon offers many of these simple chargers and they can damage your battery. The problem is that the solar panel output ranges between 11V and 24V, depending on sunlight and solar panel characteristics. You want a trickle charge at 14.4V.

 

I got a 10 W panel and charger controller from amazon for about $45: https://www.amazon.c...0?ie=UTF8&psc=1 and https://www.amazon.c...0?ie=UTF8&psc=1

 

These are not high end products, but I’m not asking much from them.

 

I was going to mount the charger controller under the hood, but did not find a good, easy location. And the charge controller and panel, anyway, stay home when we travel.

 

Another Caveat: If you install one, connect the ground wire to the truck chassis where the battery connects to the chassis. Connecting to the negative terminal of the battery can create a ground loop and mess with some of the truck's electronics.

 

 

TC 3.jpg TC 4.jpg

 

 


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2015 Fleet on 2019 Ranger


#2 Vic Harder

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Posted 21 May 2020 - 12:01 AM

If the camper is on the truck, does the default factory wiring not allow the solar panels to charge both the camper and the truck batteries? 

 

The ACR in my build allows for that.  


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#3 ntsqd

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Posted 21 May 2020 - 12:02 AM

If you have a dual sensing voltage sensing switch or automagic charge relay then after the camper's solar has bulk charged the camper battery it will close and the solar will top off everything. The hick-up in the giddy-up is that some late models can't use those and need DC - DC chargers, which correct me if I'm wrong, but those only go in one direction, i.e. truck to camper, but not also camper to truck.


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#4 Old Crow

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Posted 22 May 2020 - 02:37 PM

If you have a dual sensing voltage sensing switch or automagic charge relay then after the camper's solar has bulk charged the camper battery it will close and the solar will top off everything. The hick-up in the giddy-up is that some late models can't use those and need DC - DC chargers, which correct me if I'm wrong, but those only go in one direction, i.e. truck to camper, but not also camper to truck.

 

 Ctek's D250SA and D250SE DC-to-DC chargers have a feature to trickle-charge the starter battery. Here's how it's described in the manual...

 

"• Trickle charging of the starter battery from a solar panel. The D250SE trickle charges the starter battery from a solar panel at intervals of 3 seconds if the service battery is fully charged."   

 

There are LEDs on the display panel which indicate how electricity is flowing.   When it's trickle-charging the starter battery, the LEDs beside the solar panel icon and alternator icon are lit and the LED beside the house-battery icon is off.

 

Renogy's DCC50S also trickle-charges the starter battery (according to the manual).  It also has a visual indication when this is happening (The Alternator LED is solid red if charging from alternator to house battery, slow-flashing red if 'reverse' charging from solar panel to starter battery).  The Renogy DC-to-DC single-input chargers (which don't have the built-in MPPT controller) don't have the feature.

 

Redarc's BDDC1225D/1240D dual-input DC-to-DC charger does not appear to trickle-charge the starter battery (no mention of it in the manual).

 

I also took a look through the manuals of several Kisae and National Luna dual-input (solar and alternator) DC-to-DC chargers and could not find any indication that they trickle-charge the starter battery.

 

PS- I have a D250SA in my Tundra/Hawk rig but can't say how well trickle-charging of the starter battery works as I don't have a solar panel.  I can, however, confirm that when I charge my Tundra's starter battery with an AC-to-DC (shorepower) charger, the D250SA also charges my camper battery (as one would expect).  If I don't want that to happen, I disconnect the D250SA by pushing the button on the thermal circuit breaker.

 

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Edited by Old Crow, 22 May 2020 - 04:23 PM.

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#5 billharr

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Posted 22 May 2020 - 11:01 PM

I have always kept a battery tender on my motorcycle. Small battery and asking a lot from it. Keyless and the bike is always looking for the fob. On the camper I added a switch to bypass the isolator and the solar charges both the camper and the truck. I know not perfect but works for me. I did buy a 3A battery tender for our BMW X1 we were going to be gone for a couple of months but that did not happen.   I think AAA will be busy in a few weeks when everyones car does not start after setting for a few months. 


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#6 Jack

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Posted 23 May 2020 - 09:23 PM

The stock battery isolator makes it one-way from the truck to the camper. I do have a bypass switch in case I needed to recharge the truck battery, albeit, slowly. This would also allow the panels to trickle charge the truck battery. However, I'm at risk of doing something stupid, like, when not in use, leaving the compressor refrigerator door open (avoid mold) and not making sure it is turned off....

 

When my AGMs are ready for retirement, I'm switching to lithium. With a smart alternator, I will definitely need a DC-DC charger. It too is one way and I don't want to create a bypass. With the battery isolator, I don't get the best charging profile from the truck, but the solar mostly makes up for it.

 

Out of curiosity, I checked the FWC Owners Manual, and they don't alert users to the issues with smart alternators.


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