Charging the 12v battery from Hymotion charge port

I have a problem keeping my 12v battery charged by driving the car alone. I have an Optima yellow top battery and sits between 11v and 11.7v. I think it sits that low because my car sits about 23 hours a day. I have a short 11 mile commute each way 5 days a week and I dont think that is a long enough drive to replace what the car sucks down when its just setting there.

So I figure since I plug my car in every day to recharge the Hymotion battery why not tap into that 110v source and charge the 12v battery?

Well I bought a BatteryMinder trickle charger for the Optima battery.
BatteryMINDer® Plus AGM/OPTIMA Maintenance Charger / Desulfator-Conditioner 12 Volt – 1.0 Amp | All | Battery Chargers by BatteryMINDers.com

Cost was $59.99 plus shipping.

In order to install this in the car I need to do a few things first.

The charger inlet for the Hymotion battery is a special inlet made by Guest. The male prongs are molded to the cord that goes into the Hymotion battery charger. Now I could just cut the cord in the middle and put everything in a junction box but I'm going to try something different that should not void the warranty thats left on my Hymotion battery and provide a better connection than wire nuts. I'm going to remove the plug from the sleeve and put it into an enclosure. I'm going to attach a female socket to the original plug. From this female socket I will attach a replacement plug for the sleeve. The extra plug will cost $8 and will give me plenty of slack to work with.

You can get the plug/cord here.
MARINCO 157200-01 ConnectCharge Cord 5-15P/ROJ 6 Feet - Our Item #: 8223, Category: Inlets : StayOnline.com

Now I will also run two wires from that female connector to the 12v charger.

The way the charger works is that when you connect it to the battery it will be in a "soft off" state. An LED will light telling you that you have a good connection. It may also be doing other stuff that uses energy but I'm not to sure on how many milliamps it draws from the battery. The instructions say not to leave it connected to the 12v battery with out it being plugged in to the 110v source or you will drain the 12v battery.

So to keep the charger from draining my 12v battery when I'm not charging my Hymotion battery I will need to disconnect it on the 12v battery side.

Here is what I'm thinking that may work.

I'll take a 12v or 5v output wall wart and hook it into the 110v from the female connector. This 12v or 5v will power on a normally open relay. The relay will be connected to the positive and negative end of the battery charger. This way when there is no 110v power the relay is off and disconnects the 12v battery from the charger. When I plug in the 110v to charge my Hymotion battery it will turn on the relay and connect the charger to the 12v battery.

Now all thats left to do is to connect the 12v charger to the 110v source from the female connector.

Now with everything hooked up when I charge my Hymotion battery the 12v battery will be charged. When I unplug the Hymotion battery the 12v charger will loose power and disconnect the 12v end from the charger.

When I get time I will try to draw up some schematics to help visualize what I'm doing.

Does anyone see anything wrong with my idea or see a way to improve or make anything more simple? Anything to add?

 

Personally I would not do the ceramic heater. You could do the block heater that way but I personally like having a separate plug for it because it does draw about 400 watts. Having both Hymotion and EBH on at the same time would be pushing the limits of the wire. Add a ceramic heater and your car might go up in smoke.


Now onto my new mod.

I made a quick drawing of my idea.

Here you can see what I'm trying to do. The sockets marked with a red X are the sockets I need to buy from my local hardware store.



So far I have everything ready for the install. I found an old 6v wall wart that I will be using to power a 5v DPDT relay. The relay's only function is to connect the 12v battery to the battery charger. The 12v connection to the relay is in a normally open state that way when there is no 110v source the battery charger and the battery are disconnected from each other.

I took off the 110v male prongs on the 6v wall wart to save space. I kept the ones on the 12v charger just because I did not feel like removing them plus the added female socket will allow for better wire management in my opinion.

I have everything ready to install in a large project box. I will try to get a picture of it in the next day or two. Hopefully I can get this installed sometime this week. All I waiting to get is the replacement Guest charger plug and I need to go to the hardware store to get the one male a three female sockets.

 

Here is a picture of the components.

The project box I'm putting them in, the relay circuit, the 6v wall wart, and the BatteryMinder Optima 12v battery charger.



Here is what they will look like inside the box. I will zip tie the transformer and the charger to the box. The charger has two LEDs and a button on the front of it and I will be cutting a hole on the side of the box so I can see and use the button if I need to. I will also be cutting access holes for the wires and also drill a few vent holes to get the heat out. I may just leave the cover of the box off since its really not needed.

 

Well I have all of my supplies now.

I finished up the charger box and it bench tested OK.

Only thing left to do is install it in the car.


Here is everything installed in the box. I used 12 gauge wire for the Hymotion battery extension and I used 18 gauge wire to supply the transformer and the charger.


I cut a hole in the side of the box so I could get access to the charger lights and maintenance button.



With any luck I will have this installed next Friday.

 

I think my car PC's power supply sits on standby. But I think it only sucks down something under 100mA. I dont really remember the exact number. I do remember reading that it was so small that it would take a very long time to drain the battery.

 

I finished up the install today and so far everything works great.


After getting the bumper loose I was able to access the stock Hymotion charge port plug. All I had to do was loosen the clamp and unclip the plug from the port. The green arrow is pointing to the clip.



The cable gets routed though the vent on the side of the car.




Here is the Stock Hymotion plug and the female end of my replacement plug. If I needed to remove the charger for some reason I could plug these in together and still be able to charge the Hymotion battery.



Here is everything hooked together and working.



I stuffed everything in the hole on the left hand side where the cable comes in from the outside.



Everything gets covered up nicely.




I took a trip to Lowes and Radio Shack to gets some parts for one of my other projects and when I came home I plug in the car and everything seems to work just fine. I hope now that I have the 12v battery charging I wont have any issues with a dead battery and with the desulfation the the charger provides I hope my Optima battery will last a very long time.