View Full Version : Battery and electrical confusion
06-02-2009, 07:08 PM
Maybe I'm making this too hard, but I've read so much, and gotten so confused by everything.
Basically what I want....
Couple of house batteries
Charged from the alternator, but cut off from the engine when it's not running
Would like to be able to add a solar panel at some point to charge the house batteries, and as a bonus, trickle the starter battery too, if anything like that is made.
Seems simple enough I guess, but I still don't know what to buy.
AGM batteries, since they will be in the cabin till I can find someone that can rig up storage under the Sprinter. Optima? Other? I want to buy something that will last at least a couple of years.
Charger, controller, isolator? Anything do all that at once? I've heard the three step chargers are suppposed to be the best, but can't tell which brands are the best.
Solar. I'd do this, but I'd like to find a way to mount a big panel without drilling holes in the roof. Maybe you have to?
Wiring. I guess all the interconnects and everything have to be custom made? I guess for a tight installation, you have to measure out a piece of wire, cut, and then solder on ends for it. How heavy a gauge do you need to go for the above?
I think my needs are simple. I want to run the radio, re-wired from the dash, fridge, maybe a small microwave occasionally, laptops. Normal stuff I guess. Just want to be able to do it for a few days or week at a time.
06-02-2009, 08:29 PM
I hope I don't make you mad with my reply, but you say what you want to do is simple, but most of us pay lots of money to get what you want. Much has been already posted in this forum about batteries, solar panels, charging, length of time to charge, etc. This forum is a huge resource for you that you should search to find the answers to most of what you want. Then whatever remains after your search will be more specific than your general questions here. You should consider having the work done for you by a place like Sportsmobile. What you want to do is not simple... Al
06-02-2009, 10:16 PM
I've got $11k and 250hr's invested in my 'simple' electrical setup....so far...
06-03-2009, 12:07 AM
You were doing pretty good with your simple request until you mentioned "microwave".
The drycamping electrical world is divided into:
People who require a generator in order to run an air conditioner---not really possible with just solar and batteries. Once you go the gen route you only add batteries or solar for a little more peace and quiet.
People who only need to run low-wattage devices. They need enough batteries or a gen to run the dc bits of their rv and can use cheap, low-wattage msw inverters to power their ac electronics. Most consumer electronics have internal power supplies that convert it back to some kind of dc.
Now there is a large middle area for folks who want to run devices designed for a stick house. Microwaves, hair dryers, things with a motor. Many of these devices expect 15a of psw 110v ac. A 2000w pure sine wave inverter is not cheap. Lots of people try to cheat with two batteries and a modified sine wave inverter of less than 2000w rating. This may give you mixed results with things as simple as an electric blanket.
A popular approach would be to use an expensive Prosine inverter-charger and 4 agm batteries plus all the fuses, circuit breakers, subpanels, 2/0 interconnects, etc. Lots of quiet capability and perhaps the ability to live off alternator miles if your style is to drive the van every few days.
My generic advice is to either go cheap or go deluxe.
Cheap is limited batteries and cheap low-power inverters with a gen to run for big draws like microwaves.
Deluxe is an integrated psw inverter-charger with display, 400 ah battery bank, and all the associated subpanels and wiring protection that is involved. I have a Honda eu2000i gen to back this up but don't need it on any trip with interspersed miles.
I don't like think the middle ground is worth it because its tough on a small battery bank and maybe appliances with a msw inverter. A gen set can better replace the shore power requirement.
06-03-2009, 12:35 AM
Pretty much everything you want is available, if you keep your power demands low. The electronics are easy. The refrigerator is easy if you spend the bucks for a 12V compressor model. The microwave is pushing it. Add up the maximum watts you need for the length of time you actually use it, that's watt/hours, then size you battery bank and solar array to keep up with the demand. Everything has been written up somewhere on this forum. Another great resource for this info is Home Power magazine.
Putting the solar on the roof without holes is possible if you have roof racks. You still need to pass the wires through, so holes are tough to avoid. The biggest drawback i've found is low lying branches. Makes me want to carry a pole pruner. I plan to remount the panel below the roof rack for a little more protection.
Basically, if you have the skills required to research and build your own system, it's not hard. If this is your first and you have no experience, don't be afraid to ask, and do your research. Good luck and don't give up.
Hope this helps.
06-03-2009, 12:53 AM
If you don't feel comfortable working a fairly complex electrical installation I would definitely have a competent RV shop do the installation. You didn't mention it but you should start with the heart of the system, a good quality AC-DC/charger/distribution panel. I went with a 50 amp Inteli-power 4500 series model PD 4560. It has an automatic battery charger with the step charge wizard, which will charge the RV battery while the converter is connected to shore power. This converter is equipped with reverse battery protection , short circuit, and overload shutdown protection. Most AC-DC panels have a solar panel power input so you can trickle charge the aux. batteries from the solar panel. The best Acid Glass-Mat batteries you can get are LifeTime. They come in a huge variety of sizes/power reserve and I have had better luck with them vs.other brands I have used. Because they are sealed, AGM batteries allow you to mount them inside the Sprinter with minimal venting. The major drawback to AGM's is the very high costs. Expect to pay at least 2-3 times the cost of your cheap Lead/acid batteries. This is my cost breakdown so far for a two aux. battery, solar panel, shore power, 4 AC outlets, 3 DC outlets, 7 DC appliances and 10 LED lights: AC/DC power distribution panel $200, 120 watt solar panel $800, Solar charge controller $75, two group 27 AGM batteries $530, Have RV shop wire battery isolator and wire to power panel $300, parts to wire shore power outlet $80, miscellaneous electrical wire and supplies $250, led lighting $200, vent fans (1 fantastic, 1 bathroom fan, 2 vent fans) $350, water pump $100.
One last thing you mentioned appropriate wire ga. It depends on what you are wiring-up. A couple LED's lights drawing 10 watts would only need 16 ga. Your water pump or furnance, maybe 10 ga. or even 8 ga. When you wire your Sprinter you will use everthing from as small as 16ga. to double 00 battery cable. You can check the power draw of each circuit and then choose your ga. It would be a good idea to go up a gauge or two if in doubt. There are a couple good RV wiring books that describe each system and how they all interact. Be safe and good luck with your electrical project!
06-03-2009, 05:08 AM
Some awesome posts there. Thanks.
I had not thought of attaching the solar panel to a roof rack. Well, I did when I was looking at E350s, but I never thought of a roof rack on a Sprinter, just because it's so tall, I'm not sure how to get up there... Great idea anyway though. Yes, below the top of the rack is probably a good idea. I've already gone through some low trees in neighborhoods and had to listen to that awful sound. If I had a $1000 panel on the roof, it would hurt even more.
I hadn't really considered shore power either, since I couldn't really see using it anywhere. I've never stayed in a RV park, and didn't think I probably will, but I guess it could be useful at someone's house maybe.
You guys have convinced me. I'm ditching the microwave idea. I just figured it would be an easy way to heat up that burrito at night, but I'll just find other ways to do things. I don't want to spend needless money on a 2000 watt pro-sine inverter, just to heat burritos. That makes them some expensive food. Besides, cold Thai food is pretty decent....
I do have a hole already in the firewall where someone wired in the power for the brake conttroller I don't use, so I can run the main leads from the battery isolator through that. I have some interior decisions made that should give me a better place (safer) to put the batteries as well.
I''m going to go back to looking at pictures of people's wiring harnesses. Seems to be either really nicely done, or a rat's nest. Hopefully mine will be more the former.
06-03-2009, 05:34 AM
No need to give up on the microwave, just don't expect to run the deluxe home model...
A600W microwave will be adequately served by a 1200W inverter...
Optima batteries are not optimal for what you are trying to do...
Ideally plain old lead acid batteries work great, especially the 6V in series, but they need to go outside
If the batteries should go inside gel-cels work best as far as I'm concerned.
To separate the batteries from the alternator all you need to do is find a D+ lead under the driver's seat, just look at your legend (every Sprinter is different) and find an item that is only "ON" when the engine is running...
Simple setup for T1N
- add fuse to battery terminal in engine compartment
- run 4GA wire from engine compartment battery along the underside to under driver seat electrical compartment (there is a big rubber grommet and wire inlet there)
- hook up to 80A relay switched with D+
- Lead acid batteries next to fuel tank outside or gel cels under passenger seat
- inverter close to the batteries under passenger seat or in left sidepanel behind driver
AGM below passenger seat install thread
below passenger seat
below driver's seat
24 size gel cel batteries
galley with sink/microwave/fridge
312 diesel (closed)
06-03-2009, 09:39 PM
It is inefficient to turn 12 volts into mains via an inverter and then run large appliances. There are microwaves designed specifically to run on 12 volts. Unless you frequently intend to be hooked up to the mains when cooking that is the way I'd personally go.
If I was doing this I'd buy a pure sine wave inverter that is also capable of having solar panels hooked up to it.
The vehicles existing alternator is capable of charging up a second battery when driving along. When you start looking at dual or split charging systems you'll see all sort of voltage sensing and "intelligent" charge relays. You don't need them and they can be counter productive.
My split charge system is set up with 2 conventional relays. The first is a 180 amp heavy duty relay. What it does is connect the positive terminals of the factory and second batteries together. You MUST have a fusible link at either end of the cable connecting the 2 batteries together.
Because the current draw on a big relay is fairly high the 180 amp relay is activated by a smaller relay. This is simply powered up by the alternator exciter wire. The system therefore is simple, with the engine running the alternator is powered up and this connects the 2 batteries together. Switch the engine off at night, the relay cuts the contact between the 2 batteries. All the electrics you use when parked are run from the second battery. Even if you inadvertently run it flat the van will still happily start in the morning as the factory battery is isolated from the cabin lights, fan, inverter etc. The 2 relays, heavy duty cable, battery clamps and fusible link cost less than 50 Dollars, a lot less...
Here you can see the 2 relays on the left, the fusibe link and the cable coming in through the sock in the floor and the second battery sitting under the seat. I don't need more than that single battery for my power requirements, a proper camper van will need a bit more but the principle is the same. There is a secons identical fusible link in the engine compartment. This shot is before I properly finished it BTW.
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