DC-DC Battery Charger

[wfscot]

Hey all,

I have a Hawk on a Ram 2500 diesel. The current setup is the standard FWC wiring (separator to truck batteries) with two massive deep cycles in the Hawk (210Ah total).

Normally, the camper batteries seem to charge quite well whenever we drive for a few hours or more. That said, recently we let the camper batteries run way down and after 15+ hours of driving, the batteries were only at three LEDs (66% or so, goind to add a better monitor soon, but that's currently all we have). After talking to FWC, it seems this is quite normal as the battery separator will cycle off quite frequently to protect the truck batteries when the camper batteries are very low. They recommended plugging in which did the trick when we were finally able to do so.

That experience got me thinking about ways to improve the charging from the truck when the camper batteries are low. Beyond that, I can't help but think that the current setup is less than ideal since it is essentially a dumb charger (fixed voltage from the alternator, right?). We spend a ton of time on the road (50% or so) and we often don't have a chance to plug in. Thus I'd like to get the most out of the truck while it's running.

Does anyone have any experience with battery chargers that run off 12V? I think these are often called "DC to DC chargers". Here's one example from a quick Google search: http://www.wmjmarine.com/33313.html

In my mind, it seems a good DC-DC charger could charge the batteries better than the current setup. This would especially be true when the batteries are low since it could charge full time (instead of the cycling behavior of the separator). Furthermore, it seems it could help battery longevity and safety by optimized, multi-stage charging.

Thoughts? Any product recommendations?

FYI, we'll soon be adding a solar system. I don't think that negates any of the above reasoning, though.

Thanks!

-Scot

 

[ntsqd]

I would get the battery monitor first. We went with the Tri-Metric and I couldn't be happier, but it is not the only option and it certainly isn't the least expensive option. This is a topic that's been punted around here more than once, a simple search should yield more info than you want.

Then do the solar and size it based on your normal usage. For us that is a single 120W panel and a PWM charge controller. This also has been talked about extensively. There are PWM and MPPT contorllers. The MPPT's have a higher efficiency, but that comes at a rather dramatic cost increase. For us I didn't see the difference mattering much. For you that may different, only you can decide.
Find the Handy Bob blog on solar and read thru it. I'll warn you up front that it is painful and repetitive, but he makes good points backed with the logic behind each. He also rants a bit about the business' proclaiming to be "RV Solar Experts" and based on my limited exposure to the greater RV industry I don't think he's very far off the mark.

I've no familiarity with any of what the Mfg's use to connect the camper to the truck's charging system. I use a marine "Voltage Sensing Relay" (VSR) (AKA an "Automatic Charge Relay" or ACR) to connect them. These only connect the second battery bank when the first set has reached a full charge, and then disconnects them when the alternator stops producing power. When we are moving the VSR is more than able to keep up, though I too have my reservations about the alternator's regulator. I think that it's pretty "stupid" and have looked into marine external regulators, but their price had stopped me thus far. Yours may be external as well. Our '96 CTD's regulator is part of the ECU and is known to fail randomly. (If yours is external and in the ECU as well I suggest looking into the "gets you home" simple field repair if you haven't already.)

I considered a DC to DC charging scheme for the camper batteries, but after the solar install the need for it disappeared.

 

[billharr]

Hey all,
Does anyone have any experience with battery chargers that run off 12V? I think these are often called "DC to DC chargers". Here's one example from a quick Google search: http://www.wmjmarine.com/33313.html

$389 on sale

I like the idea but for that $$ I would invest in solar.


Check the thread on voltage gages. I added one and put a % charge sheet next to it.

 

[JaSAn]

Get a Trimetric first and determine what your power needs are. Then size your system to accomodate them.

A couple of good tutorials:
HandyBob has lived exclusively off solar since 2000
http://handybobsolar.wordpress.com/
You should especially read 'RV Battery Charging Puzzle', '9 Golden Rules', RV Solar Quick Answer'.

Also look at sailing forums. They have a wealth of information on living with house & starter batteries. The main one I follow is
http://www.cruisersforum.com/forums/f14/

JaSan

 

[K6ON]

If I had your set up, I'd simply go to West Marine and pick up a battery switch and mount it near the separator and switch around the separator if the camper batteries got low, and switch back to the separator when the camper batteries are fully charged by the truck.

I'm sort of the rebel of the group as I don't use any separator between the truck and camper. That being said, I run 2/0 welding cable through a 200 amp fuse from the truck batteries to under the back seat where I have a third battery to run high power radio gear. From there I run #6 wire to the camper through a 100 amp breaker. The camper has a 100 watt solar panel along with two large batteries, an Engel 12/110v fridge, a 1500watt inverter and a microwave. So with 5 batteries in parallel, 100 watts of solar, and a 250 amp alternator to keep them all charged when running the truck, I've sat as long as 7 days without starting the truck, the solar seeming to keep up with normal current usage.

 

[craig333]

Nah, not the only one. No separator here either.

 

[LAWNMOWERMAN]

I use a Powerstream PST-BC1212-15 DC/DC charger.The 4 stage charging system is very kind to your expensive AGM batteries.When on the road I use it to charge one battery while the solar panel charges the 2nd battery.I have been using it for almost 4 years.When in camp I use the portable solar panel to charge the truck battery and use the charger as long as there is sun.Mine cost 150.00 but I see they are up to 187.00.Iam sure the West Marine units are high quality but for 200.00 less I know what I would buy.After using a DC/DC charger I would not even consider a battery seperator. Remember, (it's not or solar),(it's and solar)!!

 

[Stan@FourWheel]

Have you thought about installing (making) a really simple bypass switch for the battery separator ?

Let the separator do what it needs to do in all normal circumstances.

But flip the bypass switch if you ever run the batteries all the way down by mistake and you are having problems with the separator kicking back & forth.

Back in the days we used to install a solenoid that way "key hot". When the truck was running it was always open and did not open & close with low voltage. It was always throwing a chrage back to the camper as needed. Those worked really well until the trucks got to complicated with their computer systems in the engine.

Just a thought.

 

[wfscot]

Thanks all for the input. I feel like I've learned a fair amount. The HandyBob stuff was very informative.

Honestly, I'm not sure I want to bypass the separator (ntsqd, pretty sure this is the same as your VSR). If my camper batteries are low, I'm a bit worried about them doing damage to the truck batteries with a direct connection (again, 210Ah total capacity for the camper batteries).

I will soon have better monitoring. I'm just trying to decide between a simple voltmeter and a full-blown shunt-based solution.

Solar is also for sure in my near future. Even with this, though, I like the idea of getting the most out of the truck while it's running.

Along those lines, I just found a device from CTEK, the D250S DUAL, that claims to provide both MPPT charging via solar as well as DC-DC charging from an alternate source (such as the truck alternator). The device seems to either choose the best or perhaps combine them. If this works, this seems like the holy grail.
http://smartercharger.com/products/dcdc/ctek-d250s-dual/

That said, from reading HandyBob, it seems that I'd like to go higher than 14.4, which doesn't seem to be possible with the CTEK. Also, the 23V limit could be an issue for solar (still figuring all that out).

LawnMowerMan, the Powerstream certainly has a good price point, but it only claims support for up to 100Ah. Also, the statement "The BC-1212-15 converts 12 volt power into 13.8 volt power for charging" seems to conflict with what I've read (e.g. HandyBob) in terms of charging voltages.

-Scot

 

[LAWNMOWERMAN]

I just turned on my dc/dc charger and it is putting out 14.5-14.6 that should make SOLAR BOB happy.On Ebay for 156.00+12.50 shipping.

 

[wfscot]

Thanks for looking into that, LawnMowerMan!

 

[wfscot]

I just wish someone would make a product that took multiple power sources (alternator, solar panel output, and unregulated convertor output) and then would combine/boost/buck as needed to provide the best charging curve to the battery. It seems like a huge waste to have multiple things all trying to charge the battery in their own way. I know there's a lot of debate on this, too, but I can't shake the feeling that they can interact in a way that causes the battery not to charge as much as it could.

That CTEK unit seems most of the way there. It only supports 2 inputs and seems to be hardcoded for 14.4 volts, but it's way closer than anything else out there. Anyone have any experience with their products?

 

[wfscot]

Just found another option. Check out this product from Sidewinder:
http://www.sidewinder.com.au/page247.html

Basically, it's a 30A fully adjustable charge controller that can handle either an alternator or solar input. They suggest either a manual switch or, more elegantly, a ignition-driven relay. It's not that pricey, either ($240 AUD). I'm checking if we can get it here in the States.

Taking the relay idea a bit further, it seems you could do a similar thing to take the convertor output (likely without the IQ4, set to something like 15.2V) and switch it into the input as well. If CONVERTOR_ON use CONVERTOR else if ALTERNATOR_ON use ANTERNATOR else use SOLAR. Sick!

 

[ntsqd]

My VSR is a BEP Marine unit. I have a "Single Sensing" because that is all that was available when I bought it. Since then "Dual Sensing" versions have become available. What that means is that if the solar has topped off the camper batteries mine does nothing further. A dual sensing would make the connection and allow the solar to top off the truck's batteries as well. When I get around to batteries on our next Runabout/Tow'd I'll move that unit to it and buy a dual sensing unit for the camper.

I don't understand what the challenges are, but it seems like a typical solar controller could have two input sources and be exactly what I need anyway. Yet all of them that I've looked at specifically say that they are only to be hooked to solar panels and not another charge source so apparently you can't even use a second one to get 4 stage charging from the alternator. This sort of thing does exist in the marine market, but hold on tight! Have a look at this: http://sterling-power-usa.com/12volt-210ampalternator-to-batterycharger.aspx

EDIT: Meant to say that Sterling has a bunch of interesting stuff, poke around their page. Might also have a look at Balmar's page as well.

 

[ski3pin]

I have been pondering on truck alternator charging of the camper battery/batteries and I am enjoying the information here. Good stuff. Keep it up and thanks for posting.

 

[wfscot]

ntsqd, thanks for pointing out Sterling. They indeed seem to have some good DC-DC chargers. Sadly they fall in same expensive range as the others ($400+).

I talked to the guy behind the Sidewinder product and he didn't seem too interested in shipping to the U.S. Bummer, as I think that would be perfect.

The more I look at the CTEK product, the more I like it. I've got some technical questions into customer support, but I'm strongly leaning that way. I'm fairly certain I could put all three inputs (convertor, alternator, and solar) into this single unit (with a relay to switch between alternator and convertor).

 

[Fyreman]

I followed the www.battery1234.com site. It was a little difficult to follow so I mostly went off the pictures. I didn't suscribe to the site but did purchase a majority of the items through amazon. It works well. The 30 amp charger is the one I use to charge my camper Batts. I run 10g fused at the battery both pos and neg back to the solar charger to the solar panel input. I have like a 2' 4g wire to the battery. It works great. I think it's a 3 stage charger with a switch for AGM and Lead Acid. Hope this helps

 

[wfscot]

So it seems the CTEK does *not* boost voltage. Thus it doesn't really solve the problem of undercharging off your alternator. It does claim to "combine" both inputs (solar and alternator), but I really have no idea what that means. At $170, I'm tempted to just buy one and see what it does.

Fyreman, you are talking about the Sunforce controller, right? So are you plugging your alternator output directly into that controller?

 

[Fyreman]

Yes

 

[Fyreman]

Well I have a positive and negative fused wire running directly from the battery terminals to the input. It only turns on and charges when the alternator is actively charging my primary rig battery.