Help Needed - installing a disconnect switch and a battery charger

[Joe & Cherie]

Guys, I have a '05 Casita SD17. I installed a Duracell AGM group 31. Nice battery! I want to install a cut off switch and full time battery charger (stop using the built in charger).

Here are my plans. I install a cut off on the neg. I have it cut off 100% of the time the rv is plugged in. I have it turned on during towing and off grid use only.

I hook up a CTEK 4.3 smart charger to my +/- leads and I plug it in to an outlet inside the rv. I never touch it again. When I am plugged in, the batt is charging or floating. When I am not plugged in, the charger is not working.

http://smartercharger.com/products/b...-multi-us-4-3/

So a few questions.

1st - I have 2 wires going to my battery + now and one of them tests 12+V when plugged in. I assume thats the wire that charges the battery from the built in charger? Is it OK to remove this wire all together? And the other one is the one that sends power from battery to the 12V lights/fridge/etc? I leave that one hooked up as is?

2nd - Will everything work like I think it should with this setup? Am I missing anything obvious?

3rd - now that I think about it, with this set up, why do I even want/need a cutoff switch to the battery? When would I ever want it turned off? What is the benefit of having it turned off when I am plugged in? The battery will never overcharge.

Thanks VERY much!!

[Borrego Dave]

I think you answered your own question in #3.

[John in Michigan]

Joe, if I understand you correctly:

(1) You have a charging wire from the tow vehicle to the battery to charge while towing.
(2) You have charging wires from the CTEK charger to charge when shore power is available.
(3) Only the battery is used to power 12vdc loads (lights, fans, etc). Thus NO converter/charger, right?

However, if you have an installed converter/charger, it should be completely disconnected from 110vac source and from 12vdc loads.

[Steve L.]

A cutoff switch eliminates phantom current drains during storage. There can be scads of them, the refrig. control board being one such load.

Not to put too fine an edge on it, if you install the cutoff in the battery compartment I'd look for a switch claiming "ignition protected" which means it switches with no chance of sparking. Combustible gasses can be found in the battery compartment as a byproduct of charging the battery.

Personally, I'd put the cut off in the positive line. Cutting the negative means the lines at/near the devices are still live (because the positive line wasn't interrupted), thus capable of being shorted to other grounds. For example through a screwdriver to a grounded chassis. Cutting the positive wire means all the rest of the wiring is dead. You can go ahead a lick(!) your 12v fuse panel without shocking worries!


As always, I'm just relating what I would do. Well, not the licking part.

[Joe & Cherie]

Thanks Guy!!!

And JohnInMI. I may have not been very clear.

I assume my Casita is 100% the way is is from the factory currently. I have 2 wires on the plus side of the battery post, and 1 wire on the negative. Where I am confused is the function of the 2 wires to the positive side. I assume of the 2 wires, 1 charges the battery (get rid of it), and one supplies 12v to the appliances while boondocked (keep it).

All I want to do is remove the "charging function" of the charger/converter (and replace it with the Ctek). I still want to use the converter function of the converter/charger for 110v/12v when plugged in.

I assume I remove the wire from the converter/charger that goes to the battery plus side and that would do it. The Ctek will replace that wire function. Then for good measure, install a cut-of switch - just because - as stated above - to remove gremlins.

This plan eliminates the "charging" portion of the stock charger/converter, but it still allows the "converter" portion to work and run my 12v from converted 110v.

Although - now that I think about it - have I just eliminated my charging during towing? I hope not!

Oh crap (sorry) I may be totally confused here. I need to go home and look at the Casita (Im at work now now and cant verify). I just looked at a picture of the Duracell on the web. I may be backwards. I may have 2 negative wires on the battery and 1 positive. If so, now I'm more confused.....lol.

Still the same goal tho. To eliminate that "charger" while maintaining the "converter". Sorry for all the confusion here!!! Its coming from me.....haha.

Let me go home and check this out then reply again!!

[John in Michigan]

I just PM'd Joe and Brian. I'm not familiar w/Casita wiring, but recommend isolating both the CTEK charger and the battery from all 12 vdc circuits/loads while connected to shore power.

(Also, Brian pointed that the CTEK 4.3 amp charger will struggle to completely charge the 100 amp hour battery.)

[John in Michigan]

Joe, on my Trillium I'm planning to:

(1) Isolate my CTEK 4.3 charger and 38 amp hour AGM battery. Plug the CTEK into a newly added 110vac outlet in the camper, inside a cabinet.
(2) Use a SPDT switch to switch all 12 vdc loads in the trailer between the converter (when on shore power) and the battery (when boondocking).
(3) I don't have a vehicle charging wire. I don't believe the vehicle charging wire will provide much charge to a 100 amp hour battery, unless the wire is heavy gauge.

[Joe & Cherie]

I can see how this topic can get so deep....ha. I understand somewhat all this stuff. Pretty much actually. But I start to fog when we start talking 4.3 not being enough to charge, etc.

Brian recommended to put a cut-off on the POS battery cable. Then install the Ctek on the battery side of that cut off switch. This will do exactly what I want! Unless - I or the Mrs accidentally leave the cut off switch on while plugged in to shore power. We can manage that risk with diligence.

John recommended to remove the battery and Ctek from all 12v circuits while on shore power. I think the solution above does both (?) because the battery and Ctek are both connected to the batt side of the cut off switch.

So why do I have a 4.3 Ctek with the grp31 AGM? Well, I bought the AGM because it was the biggest bugger that would fit!! I already have the 4.3 and I use it on a vintage car which is driven seldom and has an Optima in it. The car is getting sold to further pursue my new hobby of egg-camping!! So I have a spare 4.3 laying around. The 4.3 was recommended for that Optima so I "assumed" it would be ok for the egg and there is where the fog enters my brain - I dont know enough about the details to know if its ok.

At this stage in our egg life, we still have to work, so we are weekend or week long vacation campers. Our destinations will either have power or they wont. When we do get shore power, it will be plugged in for a long time (home).

So that being said - I'm not concerned about the 4.3 charging the 100 amp hour battery slowly, but I am concerned if it cannot charge if fully.

John - I am also adding a 110v outlet in a cabinet to plug in the Ctek. I am unclear about why the SPDT is needed? Doesn't the converter just convert when shore power is on? And then I run off the battery 12v when no shore power is avail and I turn the cut off switch to the ON position? Is this not the same thing?

Thanks guys - this is a great thread!! You guys are great help!!

[John in Michigan]

Joe, the advantage of using a SPDT switch instead of a cutoff switch, is that it doesn't matter if you forget.

[John in Michigan]

Concerning the use of the CTEK 4.3 amp charger, it looks like you should be OK. The description says:

- Charges batteries up to 110 amp hours
- Maintains batteries up to 160 amp hours

[Steve L.]

The last time I researched AGM batteries I opted to not go there. For the size they weren’t very energy dense (amp-hours). Looking at the web, the 31M is rated at 75 amp hours vs the approximately 100 amp hours for the smaller group 27 I have shoehorned into my 16’s battery compartment. And I could buy multiple lead acids for the price of AGM. Still, little or no out-gassing during recharging.

But beyond that I must be missing something in your post because all the Ctek 4.3 chargers I found on their website have a warning that the charger is for lead-acid batteries only. There are definitely different charging requirements for lead acid vs AGM.


Edit note: I now see that there is a switch for AGM so you're covered. And AGM are lead acid but not "wet" acid.

[Joe & Cherie]

Originally Posted by John in Michigan

Joe, the advantage of using a SPDT switch instead of a cutoff switch, is that it doesn't matter if you forget.

I'm still throwing my head around this. This will guarantee that your 12v loads will only use the converter or the battery. But I still would need the cutoff to make sure the charger/converter doesn't charge the battery when on shore power - no?

Steve - here is the AGM specs. I just wanted the freedom to not be checking water - even if at a performance penalty.

I leave the Ctek 4.3 on "snowflake mode"

Specifications
1 amp hour rate:68.2
100 amp hour rate:110
20 amp hour rate:105
3 amp hour rate:85
5 amp hour rate:86
6 amp hour rate:87.4
8 amp hour rate:90
Battery Electrolyte Composition:Glass Mat
Battery End Type:Top Post
Battery Purpose:Starting Lighting Instrumentation
BCI Group Size:31
CCA at 0 degrees F:800
Freight Class:65
MCA at 32 degrees F:1000
Minutes at 15 amps:348
Minutes at 25 amps:210
Minutes at 5 amps:1265
Minutes at 50 amps:87.4
Minutes at 75 amps:53
Minutes at 8 amps:706
Polarity:Left Positive
Reserve Capacity:200
Terminal Type:STUD/SAE
Volts:12

[John in Michigan]

"I'm still throwing my head around this. This will guarantee that your 12v loads will only use the converter or the battery. But I still would need the cutoff to make sure the charger/converter doesn't charge the battery when on shore power - no?"

Joe, the SPDT would disconnect the battery from all 12 vdc circuits on the trailer except the CTEK 4.3 when switched to shore power mode. When switched to battery (boondocking) mode, the battery would be connected to all 12 vdc circuits.

And of course the CTEK 4.3 would remain plugged into a 110 vdc outlet at all times, but only powered on when shore power is available.

[Joe & Cherie]

OK - I think I got ya! But I think I'm doing the same thing by using a cut off switch on the positive battery cable, and then permanently connecting the Ctek directly to the battery posts and permanently leaving the Ctek plugged in to a 110v outlet.

When cutoff switch is OFF (shore power mode), the switch would disconnect the battery from all 12 vdc circuits. The Ctek would be charging because its plugged into a live 110v outlet.

When cutoff switch is ON (boondocking mode) the battery would be connected to all 12 vdc circuits. The Ctek would still be hooked up, but plugged in to a dead outlet so it wont be doing anything.

I seriously apologize if I'm missing the obvious!!

Maybe I am discharging my battery faster by having a charger hooked up to it even tho its plugged into a dead outlet?? Am I back-feeding the 110V lines with 12V battery power?? Therefore the switch to cut it off is required??

[John in Michigan]

Joe, I agree that the cutoff switch should accomplish the same goal as the SPDT.

The reason to isolate the battery with a switch?
(1) That's the best way to ensure it gets fully and properly charged.
(2) As others have mentioned, you can also use the cutoff switch to prevent the battery from being discharged when the camper is not being used.

[Joe & Cherie]

Thanks John! I just needed to understand. I dont want to do it wrong. But you do have me thinking about the SPDT because Im starting to 2nd guess the idea of the Ctek hooked up and plugged in while boondocking - even tho the 110v outlet is dead. As was mentioned earlier, and your reasons too - gremlins. The SPDT kills that gremlin path and does seem like a solid approach.

I sincerely appreciate it John, and all who helped me! I think I have a plan!

[steve dunham]

The charging portion on my Scamp converter failed . I cut the leads from the converter's charger (line side) in half and taped off the half coming from the converter's charger. I then took the 12 VDC leads from my new smart charger and hooked them up to the half of the wires going to the battery / converter (Load ). Everything will work as it normally does . You could also put a SPDT switch in line as mentioned above so you could run either charger to charge your battery.

[John in Michigan]

Joe, in boondock mode, the CTEK charger would still be attached to the battery. You could simply disconnect the CTEK charger from the battery. It comes with a quick disconnect charging cord. Even if you don't, according to the CTEK charger manual, this charger has only 1 amp hour per month back current drain. "Back current drain is the current that drains the battery if the charger is not connected to the mains. CTEK chargers have very low back current."

[Joe & Cherie]

Well I have her finished! I installed a battery cutoff switch inside the Casita which is cutting off the positive side. Then I installed a new switched 110AC recepticle outlet off of the spare breaker and plugged the ctek into it. Then ran the +/- leads on the ctek to 2 more dc switches. Then from those switches to the battery +/- hooked up the the battery side of the cutoff switch.

Now I can switch the battery off and on, I can power the charger off and on, and I can switch off the leads going from the charger to the battery to prevent any back current. Now I never enter the battery compartment!

I charge battery while its plugged into shore power and switched off from the Casita. I turn off the charger and I switch off the ctek +/- leads while battery is on for boondocking!

All switches and outlet are under the side dinette seat so no visible stuff.



Thanks EVERYBODY for your help in this topic!!

[John in Michigan]

Joe, that's a great setup. Let us know how it works out.

-John