Second Battery Help

[Quint]

Ok, I've searched the previous messages but I'd like some more opinions. I want to add a second battery to my camper. I'm currently run off the truck starter battery an Optima Yellow Top deep cycle. This works ok as I don't have that many power needs until now. I just bought a Waeco (Dometic) 12v CF-25 fridge and need more power so I don't run the starter down too much. My plan is to move the Optima to the camper and buy a cheap starter battery. My question is what do I need to do this? Do you have suggestions for a battery isolator,etc? I'll probably be paying an RV shop to do this but I want to buy the parts and have them install them unless it's easy. Thanks in advance.

 

[Phird05]

Ok, I've searched the previous messages but I'd like some more opinions. I want to add a second battery to my camper. I'm currently run off the truck starter battery an Optima Yellow Top deep cycle. This works ok as I don't have that many power needs until now. I just bought a Waeco (Dometic) 12v CF-25 fridge and need more power so I don't run the starter down too much. My plan is to move the Optima to the camper and buy a cheap starter battery. My question is what do I need to do this? Do you have suggestions for a battery isolator,etc? I'll probably be paying an RV shop to do this but I want to buy the parts and have them install them unless it's easy. Thanks in advance.


Hey Quint,

I too, have a dometic. Mine is a 3.8 cubic ft. 3 way Fridge/Freezer. I'm a little new to this but my camper has two deep cycle batteries, and the only time I run the fridge on DC is when I am driving so they are in "charge" mode while I am driving. I once forgot to switch it over to gas when I was in the middle of nowwhere, and the batteries ran down incredibly fast. The DC mode on any fridge sucks the life out of batteries very quickly. I would suggest only running your fridge on DC when you are at a hook up or you are driving your truck. Other than that use the gas mode when in camp and your truck is not running. Honestly, I'm not sure what you mean by running the starter down. Is your fridge a 3 way?

I hope this helps.

Paul

 

[rich]

Hey Quint,

I too, have a dometic. Mine is a 3.8 cubic ft. 3 way Fridge/Freezer. I'm a little new to this but my camper has two deep cycle batteries, and the only time I run the fridge on DC is when I am driving so they are in "charge" mode while I am driving. I once forgot to switch it over to gas when I was in the middle of nowwhere, and the batteries ran down incredibly fast. The DC mode on any fridge sucks the life out of batteries very quickly. I would suggest only running your fridge on DC when you are at a hook up or you are driving your truck. Other than that use the gas mode when in camp and your truck is not running. Honestly, I'm not sure what you mean by running the starter down. Is your fridge a 3 way?

I hope this helps.

Paul



Hi Quint,

If you are talking about rigging a secondary battery system for the camper there are two ways to do it the fancy expensive way and the old school cheap way. I can't explain the fancy expensive way but the guys at ATC for FWC can do that for you. The cheap old school way involves some wire, a two post fuse box and a four post solenoid. You tap off of the positve on the truck battery and run that to one of two posts on the two poster which you mount on the wheel well or fire wall in the engine compartment. You then take another power wire, 14 gauge should do it to one of the two gold posts on your solenoid which you have mounted on the fire wall near your windshield wiper motor. You tap into the hot wire for your windshield wiper motor with just a clamp on tap and jump that with some 14 guage wire over to one of the silver posts on your solenoid. You then have two posts left on your 4 post solenoid, one of them you run a wire to ground somewhere and the final gold post you take a wire and run it to the positive post on the deep cycle battery for the camper which you can put between the wheel well and cab if you have room or put inside the camper if you don't.

The reason you tap into the windshield wiper motor is because it's only hot when the key is on so when the truck is running it will charge your deep cycle and when it's off it can't draw down your main starting battery. Most vehicles the wiper motor is only on with the key but buy a test light for $6 and make sure the power wire for your wiper motor is only hot with the key turned before using it, otherwise you could draw down your main battery.

This doesn't involve fancy isolator switches or systems but I am told that it works great and guys have been using this system for decades without a problem. I just bought the components for about $40 and will be rigging it up for myself on my fleet soon, I'll post pics of the install when I'm done. I'm sure someone here can explain the fancier system to you.

Good luck!

 

[Quint]

Thanks Rich. I think I'll try your way unless someone can give me a good reason not to. It sounds quite reasonable and straightforward. Anyone?

 

[rich]

Yeah, I wouldn't mind opinions on it myself since I just got the parts and haven't rigged it yet I talked to Marty at ATC while he was mounting my corner jacks and he said that it's a reliable old school way to do it. I can't say enough about the guys at ATC by the way. They are knowledgeable, friendly and helpful. My camper is a bit of a project and they are more than happy to take the time to walk me through some of the necessary repairs and they are reasonably priced and honest to do the repairs that I don't want to tackle. I had a wonderful experience there at the factory with them.

 

[Quint]

Rich,
Where did you get the solenoid? Do you recommend any particular model or maker?

 

[cmck]

looking to do a similar set up myself, keep us posted on the progress...

Chris

 

[rich]

Rich,
Where did you get the solenoid? Do you recommend any particular model or maker?


I went to Allied trailer supply in Sacramento, it's not too far from the ATC factory, they recommended Allied so I went over there while my jacks were being mounted and the guy there pulled one of the shelf and said this is what you need and then laid all the parts on the counter and showed me the whole system. I'll look at the solenoid tomorrow and see if there is a name or part number on it. I'm sure any local rv supply store would have something similar, even an auto parts store like Kragens or Napa might have them.

 

[pods8]

Thanks Rich. I think I'll try your way unless someone can give me a good reason not to. It sounds quite reasonable and straightforward. Anyone?


Devils advocate from my reading:
One thing to consider (you can decide if its really an issue) is when your axillary battery is rather drained and than solenoid connects it to your other battery you'll have a large amp rush to the secondary battery. Main issue with that is its not good for either battery, can roast out wire/components if they aren't sized appropriately, and if you happen to turn off your truck too soon before the starter battery gets recharged you're SOL when you try to start again.

Additionally solenoids can fail and get stuck with the connection made (which will kill your truck battery), not sure how likely that actually is though.

However the old school method has worked to an extent for years so its got that going for it.



The setup I'm installing now is in the "fancy" category. I have some AGM batteries that wouldn't charge too well off the alternator system so I have a DC-DC charger in between the truck battery and axillary battery. Its like an amplifier and has a "remote" line that needs to be energized which I have on an ignition hot switch (basically the same as rich's wiper motor setup). However the charger is only pulling a certain number of amps so it'll avoid a larger current inrush and its on a switch so I can wait to turn it on until I'm out and on the road rather then just starting the truck for a second or something. All that said optima's are supposed to charge decently off an alternator so I'm not saying you'd want to go down the same route.

 

[rich]

Devils advocate from my reading:
One thing to consider (you can decide if its really an issue) is when your axillary battery is rather drained and than solenoid connects it to your other battery you'll have a large amp rush to the secondary battery. Main issue with that is its not good for either battery, can roast out wire/components if they aren't sized appropriately, and if you happen to turn off your truck too soon before the starter battery gets recharged you're SOL when you try to start again.

Additionally solenoids can fail and get stuck with the connection made (which will kill your truck battery), not sure how likely that actually is though.

However the old school method has worked to an extent for years so its got that going for it.



The setup I'm installing now is in the "fancy" category. I have some AGM batteries that wouldn't charge too well off the alternator system so I have a DC-DC charger in between the truck battery and axillary battery. Its like an amplifier and has a "remote" line that needs to be energized which I have on an ignition hot switch (basically the same as rich's wiper motor setup). However the charger is only pulling a certain number of amps so it'll avoid a larger current inrush and its on a switch so I can wait to turn it on until I'm out and on the road rather then just starting the truck for a second or something. All that said optima's are supposed to charge decently off an alternator so I'm not saying you'd want to go down the same route.

PODS,

I like what you have going on there, how much does the dc/dc charger cost?

 

[Bat]

Look into the Sure Power 1314 or 1315 simple connection with good protection

 

[pods8]

PODS,

I like what you have going on there, how much does the dc/dc charger cost?


I got a 7.5amp model (this one used to be able to switch between 7.5 and 15amp so I might look into that at some point if the 7.5A doesn't keep up, however I figure drive time verse amp usage will likely balance out enough that I'll keep the batteries more or less topped off) which runs $150: http://www.powerstream.com/DCC.htm Its a bit of a premium in cost compared to isolators and such but if I'm getting the charge profile I want I think it'll be worthwhile in the long run.

Promariner makes a higher capacity (something like 40amp) but those are spendy.

 

[HERR42]

i was going to post this...and pods beat me to it....but here goes.

For those of us who have added a second battery, and specifically a 2nd AGM battery (such as the Interstate DCM0075 or an Optima), The issue of blowing fuses when attempting a parallel charge warrants a good look.

As delivered, the combination of the camper wiring, the Pollak 30 amp thermal breaker, and the Sure Power isolator work well but cannot handle the addition of a second battery.
The usual problem is exceeding the capacity of the 30 amp thermal breaker. The breaker is properly sized for the existing wiring. Charging two batteries in parallel can exceed 30 amps.

For multiple reasons outside the scope of this thread I am unwilling to entertain/carry a gasoline powered generator.

For my application I would like to be able to recharge a 2nd Optima battery in the camper. I might have removed the battery to discharge it, and then reconnect it to the charging system. This means it could be discharged far below the house battery.

Requirements:

1. Charge AGM type battery at 10 amps minimum – 30 amps max – for speed
2. Input source would be the 12v engine starting battery / alternator
3. 30 amp maximum charge current limit – as specified by the manufacturer, Optima and Interstate
4. Protection for over temp, under voltage, etc.


I suppose adding a second wire feed from the vehicle with its own 30 amp thermal breaker and isolator is an option.
When the battery is discharged low enough the breaker will cycle thus limiting charge current…this is not a “good” solution and I don’t want to add more wiring.

Another possibility is to insert one of these types of products into the existing wiring and use it to charge both batteries:

http://www.analyticsystems.com/Original%20Site/products/bcd305.htm

or this might be best … http://www.surepower.com/pdf/trailchargerflyer.pdf

example of use of “TRAIL CHARGER” ftp://ftp.maxonlift.com/TechPub/msheets/M-05-03A_EO11020.pdf

how long does the powerstream unit take to recharge the optima?
have you considered removing the isolator?
what about the interaction between the converter and the solar charge controller?

lots of questions...

 

[Mark W. Ingalls]

Interesting discussion...

 

[Stan@FourWheel]

have you thought about putting a marine battery switch in-between the batteries ?

should be somewhat quick & easy.

i did this for my camper and it works great !!

the switch is approx. $ 30.00 - 50.00.

the batteries like to be separate anyway.

that way if you have one bad battery, it won't eventually suck down the other good battery.

one day I have the switch on #1 when i'm driving.

the next day I have the switch on #2.

you won't be drawing too many amps that way.

I always have a full battery that way.

in an emergency I can use both batteries if I need to (haven't yet)


http://www.bluewatermarinesvc.com/html/bat_switch.html








.

 

[HERR42]

i though of that. the problem is this: what happenes when i have really run down one of them? there are some pretty heavy currents when you reconnect.

 

[rich]

To be clear, Herr42 and Stan, you are talking about two batteries in the camper in addition to the vehicle/starting battery correct?

 

[HERR42]

To be clear, Herr42 and Stan, you are talking about two batteries in the camper in addition to the vehicle/starting battery correct?

yes.

 

[pods8]

http://www.analyticsystems.com/Original%20Site/products/bcd305.htm

A quick look online has that at over $800.
This one handles a good load but is likely going to come at a cheaper price tag (relatively speaking): http://www.pmariner.com/productFeature.php?ProductNum=05504

I'd go solar before one of those. The powerstream was a lower cost option to me with the compromise of slower charge rates.

or this might be best … http://www.surepower.com/pdf/trailchargerflyer.pdf

example of use of “TRAIL CHARGER” ftp://ftp.maxonlift.com/TechPub/msheets/M-05-03A_EO11020.pdf


Lacks stage charging if that matters to you at all.

how long does the powerstream unit take to recharge the optima?
have you considered removing the isolator?
what about the interaction between the converter and the solar charge controller?


These questions to me? The power stream is sitting on the floor of the camper waiting to be wired in when I get back tomorrow night from 10days of work travel so no data yet. I'm leaving saturday for 2weeks on the road with the camper and should have some data then.

I don't have an isolator just an on/off switch that is powered by an ignition hot, again assuming you are talking to me.

I don't have solar but have thought if I do pursue it down the road and buy something under 7.5amp that I could get away with a cheaper PWM controller and input it into the powerstream to obtain stage charging without having to buy a more expensive MPPT charger with stage charging. Do note that you'll be loosing efficiency with a PWM controller verse MPPT though.