Electrical 101: advice for noob?

kadave

New member
I’m working on my van conversion (2008 Sprinter 170”) and need some advice so I can start sourcing parts. The electrical seems the most daunting part of the build. Note: I don’t plan to run any solar. I’d like power sources to be shore power and charging lithium battery from alternator. This van will be a weekend family camper and to park in driveways of friends/family.

120v - I have a Dometic Penguin II A/C system. It will be the only 120v item in the van. Shore Power ONLY.

12v - Water pump, maxxair fan, diesel heater, leds, fridge, etc.

Question: Since A/C is shore power only, should I get a traditional RV power converter/breaker box? Should I just run all 12v devices from battery via a 1000-2000 watt inverter? I‘ve read about the inverter-chargers, but I’m trying to get by with 100ah lithium battery. Appreciate any advice.

kadave

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sparkplug

Active member
The casually listed "fridge" could play an important role in this calculation.

If you're talking about a low power consumption compressor fridge like the dometic etc then you have less to worry about electrically speaking than if you're planning to just install a household fridge.

However you said the Penguin is the only 120v item, so I'm going to assume you have a compressor fridge.

To be honest I would probably use the shore power to run the Penguin and a standard battery charger (one which is specifically capable of providing the right charging profile for Lithium batteries).

Connect the battery to the charger when you're on shore power (you could do this with a simple isolator switch)

Then simply run cables directly from your batteries into a voltage regulator (you can buy them for $5 or less) and into a fuse box. The regulator means that your fuse box only gets 12v not the 13v+ which the charger will be pumping into your battery. It probably isn't strictly speaking required but for a couple of bucks it should be no biggie.

Of course you would still have a DC to DC (or B2B) charger so that the battery is charged from the alternator when driving.

Just in case you're not familiar with voltage drop and why it might be an issue with your fridge and heater then I suggest having a read of this short but helpful article on cable sizing.
 
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kadave

New member
Thanks sparkplug! I appreciate the resource on voltage drop - which I hadn’t considered.

Yes, 12v dometic fridge for low power consumption.

So you recommend I go with a traditional RV converter/breaker for the A/C unit? I think some RV converter/breakers also power DC so I could charge my 12v lithium battery while on shore power. And a DC to DC battery charger to charge while driving? I will do more research on a voltage regulator so the fuse box will get consistent power.
 

sparkplug

Active member
Don't know much about shore power and converter / breakers - but lithium batteries require higher voltages to charge than agm etc so make sure that whatever is charging that battery is designed to do the job.

Like I said, not sure how important the regulator is. I don't have one, but then I'm not pushing 14v into my leisure batteries. A lot depends on the maximum voltage that the devices you're planning to connect will withstand. A regulator would be an inexpensive piece of mind thing to fit IMO.

Now that I've mentioned it I'm half tempted to fit one myself. If it stops anything working then it's easy to bypass and won't have cost much.
 

Midwestdrifter

Engineer In Residence
You need to do a budget to determine how much storage you need. That will allow you to size your system appropriately, and save yourself time and money.

Are you certain you need lithium? For modest usage a lead acid system may be much cheaper.

Inverter chargers are only necessary if you have 120V items you need to run from battery power. If they are only low power users, like chargers etc, a separate inverter may be a better deal. Combined with a lower current shore power charger. Inverter chargers are a good option for builds that need 120V from battery power at higher currents, and also need a high rate shore power charger.
 

Midwestdrifter

Engineer In Residence
but lithium batteries require higher voltages to charge than agm etc so make sure that whatever is charging that battery is designed to do the job.
This is not true. While some MFG suggest using high charge voltages, this may be due to a limitation of their balancing design. LFP packs by their chemical nature charge just fine in the 13.9-14.2V range.

FYI, an 08 model will have a single voltage alternator, which is typically between 13.6-14.1V. This is suitable for charging most lithium packs, though occasional shore power charging may be needed to complete a balance cycle, depending on the design used.
 

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