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Before we begin: I am armed with a whole lot of internet "research", not much experience with or knowledge of electrical systems, and a DIY mentality. I'm good at digging holes for myself.

I recently sold my diesel PM and am designing the electrical system for a new build.

Because we had that diesel build for ~4 years, and don't intend to deviate substantially from the way we used it, we have a very good handle on what our electrical needs will be.

I've calculated our energy usage at ~229 amp hours per day. I rounded up everywhere, and sometimes rounded up again -- just to be certain that I wasn't shorting us on battery storage.

The two main draws will be a NovaKool fridge/freezer and an induction cooktop. The induction cooktop will be our only (planned) use of an inverter. It'll be used to boil water for my sweetie's chai in the AM, and to cook a simple meal in the evening. Pretty limited usage.

Which brings me to my first question: When estimating power needs, do you actually assign a value to the inverter? Or do you figure some amount of loss from the DC -> AC conversion?

Second question pertains to skipping the solar on this go-round. I had 200w of solar going into 2 x 100AH AGM 6v batts on the last build. It was always full (magic!) except when visiting the PNW in winter. For those trips I became reliant on a relay to charge the batteries as I drove.

I used solar on the last build because I envisioned boondocking for days at a stretch without moving or even starting the van. In reality this happened rarely -- maybe 3 times per year, and at most it would be 2 days in place and then we'd drive somewhere else, or home. In short, we could easily have done without the solar and just used the relay.

I'm considering just skipping the solar this time. If I did that I'd put some of the $ saved toward 400 - 450AH of AGM's. And maybe a real DC to DC charger instead of just the simple relay.

Anyone wanna tell me not to do it? Anyone wanna tell me it's a great idea?
 

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Hi Mikesee

I think the 1st step here is analyzing your stated 229 AHr per day need.

Do you have a spreadsheet or chart with your calculations? If so please post it & the other DIYers can evaluate your 229 AHr / day total.

The opinions you get on electrical design should come from the assumed loads. Primary design requirement.

Regarding solar & PNW; I hear ya,,,I live in the Canadian PSW just north of the PNW & winter solar does not pencil (we carry a Honda 2200 Generator & plug it into our Shore power if need be). We mostly charge direct from the PM 180 alternator via red POS fuse upfitter 70Amp on top of the starter battery.

You are doing the right thing in asking before you build (or even design)馃憤. So many novice DIY build and then ask for help.
 

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I thought the same thing, I actually planned and even bought components for solar, but due to surgery did not have the time to get and install panels before I had to hit the road, So I had a solar charger controller, sitting in the van, not connected in the event I decided to add solar later.

I figured that I would drive often enough to charger the batteries. Now my batteries are rather large (600 amp hour LiFePO4) and I was running a battery to battery charger (60 amp Sterling). My plan worked out just fine for while, as I never am in one place for more than two days at a time.

Life was good until the batteries were low and I was on a long drive. The sterling decided to melt down in the northeast in the winter. (no campgrounds open where I could pay for a night and charge, no other way to charge the batteries). At that moment I wished I had solar. I ended up ordering 200W of solar panels and installing them in the RV parking lot of a casino. By the time I got them up there my battery was down to about 20% (I was still using it, but had unplugged the fridge and was using an ice chest, I was also cold because I reduced heater use). The batteries started to recharge (slowly as 200W into 600AH is not a lot) and in the northeast winter I was only getting 125 watts due to the angle.

If you go the relay route, I think the risk of a failure is low. The problem with a relay on a large battery bank with AGM batteries is the long time it takes to get the batteries fully charged. There is a long tail time with AGM batteries, so you can get to 80-90% pretty quick but to get fully charged it takes a long time. A battery to battery charger can help, but that is a point of failure. Lead acid (AGM) batteries like to be kept charged.

This isn't to say lithium batteries don't also have problems with alternator charging (they do) they are just different problems. (low temperature charge prevention, current limiting, etc)

Bottom line, it didn't work for me because I was staying in the van and had no way to charge the batteries when my Battery to battery charger failed. If for nothing else the solar is a good backup.
 

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I second the need to reassess numbers. You're needs must have grown greatly from the previous build. 2x 100ah 6v lead batteries only provide 50ah usable. ~1/5 your intended use. Are you regularly on shore power?

As for your actual questions.
1) an inverter efficiently of ~85% is safe for calculation. Actual numbers depend on the unit.

2) this is a choice for you. Most here advise solar. Main thing is that you need to maintain power in for power out. The 400-450ah bank you stated you could afford instead of solar will still struggle to support 229ah daily usage.

Something tells me the numbers provided aren't accurate. If they are, I wouldn't skip the solar unless you don't get sun, as you'll want as many options as possible to recharge
 

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We gave this discussion a concussion in another thread within the last week.
I know what you mean, and can sympathize with your pain, but will respectfully disagree.

Electrical system optimization depends way too much on its intended use, and also on available resources. What鈥檚 best for one guy who mostly powers a small fridge, camps for days in the desert, and doesn鈥檛 drive/tour long distances daily may not be close to what another guy needs. This difference is magnified by different budgets. If each person is helped individually, the discussion may be quite different in my opinion. Or not.

Let鈥檚 hope for greater OP participation so as to stay on topic. :)
 

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I will add that I noticed but did not address the battery size and usage issue. Pretty high usage. I only have that kind of issue if I run my AC off the battery, otherwise I stay under 80-100 AH a day (from memory, don't quote that)
 

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.....cut....

Because we had that diesel build for ~4 years, and don't intend to deviate substantially from the way we used it, we have a very good handle on what our electrical needs will be.

I've calculated our energy usage at ~229 amp hours per day. I rounded up everywhere, and sometimes rounded up again -- just to be certain that I wasn't shorting us on battery storage.

.....cut....

Second question pertains to skipping the solar on this go-round. I had 200w of solar going into 2 x 100AH AGM 6v batts on the last build. It was always full (magic!) except when visiting the PNW in winter. For those trips I became reliant on a relay to charge the batteries as I drove.

.....cut....
Your estimate is very different than your previous equipment could support under normal conditions, so as a first step, could you explain why the estimate is so much higher or how you got close to 200 Ah daily?

The solar component, at 200-Watt nominal, should make around 600 Watt-hours daily on average, or 50 Ah. That鈥檚 a long ways from 200 Ah daily.
 

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Okay, correct me if I'm wrong anywhere. I'm about to write way too much stuff. I've been thinking about it, and it's the induction that is new, or was only utilized on shore power, right?

If you're only using it on shore power, ignore it from your battery usage calculation and you needn't bother with the rest of my ramblings either (unless interested). If you intend to operate it from the batteries, they will not appreciate it. Let's do some depressing maths.

Deep cycle batteries are designed to release their charge over an extended period, normally 20 hours (capacity/20). They do not like high amp usage (surges more or less have a smaller impact). Medium heat(50%) on a 1500w stove would be roughly 75ah draw. To avoid battery damage over prolonged use, your bank should be as close to 1500ah(1500/20=75) as possible. Obviously this will not be in use for 20 hours at a time, but depending on the batteries they may not even allow a surge like that without sufficient total capacity.

This size is extreme and fairly unachievable in a mobile environment. I've cautioned against electric heating prior, and as an electrician the 12v 2000w+ inverters scare me in availability. The wire size to safely power these is massive, the amp draw is extreme, and I would highly recommend changing over to 24v, 36v, or 48v for such contraptions (as is common in non-mobile off grid applications)

On the other hand, I know people have hooked these things up. Personally I think gas cooks better even in houses. I don't have the same idea that gas is more dangerous than electricity though. 12v power doesn't stay at harmless levels when the amperage is high.
 

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My 2/12V 105ah AGM鈥榮 have always powered my 2k inverter fine and after almost six years both work as well as new - just sayin鈥欚煠
 

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.....cut....

Deep cycle batteries are designed to release their charge over an extended period, normally 20 hours (capacity/20). They do not like high amp usage (surges more or less have a smaller impact). Medium heat(50%) on a 1500w stove would be roughly 75ah draw. To avoid battery damage over prolonged use, your bank should be as close to 1500ah(1500/20=75) as possible. Obviously this will not be in use for 20 hours at a time, but depending on the batteries they may not even allow a surge like that without sufficient total capacity.

......cut.....
Trojan and other battery manufacturers often rate deep-cycle batteries at 5, 10, 20 and 100 hour discharge rates. Additionally, Golf Cart deep cycle often list 25 and 75 Amp discharge rates, expressed in minutes they can hold that current (Reserve Capacity).

In the case of the very popular Trojan T-105 Deep Cycle flooded battery, the listed 75-Amp capacity is 115 minutes, or just under 2 hours. If limiting to just under 50% SOC, that equals to 1 hour at 75 Amps. Not saying that鈥檚 ideal, but 20 hours isn鈥檛 a real limit either. Normal golf carts could not operate for 20 hours straight on a single charge.

While in high school I worked on a ranch one summer where an electric feed cart ran batteries down in 2 to 3 hours twice a day (morning and evening) and they lasted a long time.

Trojan rating for T-105 Deep Cycle flooded golf cart battery below:
1905429E-A7C6-4EEC-8B81-21BCC01C41DF.jpeg
 

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I thought you had relatively minor electrical usage KOV? It doesn't actually draw 2kw unless that's the draw on it. The full 2000w would take roughly 200ah draw (c/1 in your setup) and completely drain your recommended usable capacity (50% DoD) in half an hour under max load. A short surge would likely bear less impact on quality batteries, but that's not sustainable for prolonged used
 

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This size is extreme and fairly unachievable in a mobile environment. I've cautioned against electric heating prior, and as an electrician the 12v 2000w+ inverters scare me in availability. The wire size to safely power these is massive, the amp draw is extreme, and I would highly recommend changing over to 24v, 36v, or 48v for such contraptions (as is common in non-mobile off grid applications)
I don't cook, but you probably would not like my 3000 watt (VA really) 12 V inverter. The wires are indeed massive! And I used to work as an electrician and have a degree in electrical engineering so its safe.
Truth be known I've never drawn more than about 1000 watts off it at a time (microwave), I've actually had more power running the other way when I was charging on shore power (120 amps continuous for several hours!)

As long as you have the right wiring and battery bank size I don't think its a problem. I also don't think the battery bank has to only draw the 20 hour rate to be happy. Quite a lot of AGM and lead acid batteries (and of course Lithium of various chemistries) are used in applications where the short term draw is quite high, such as golf carts (which use a higher voltage for the reasons you describe, but they generate very high currents even at these higher voltages when accelerating).

I think more people would consider higher voltages, it just creates more complications as so many vehicle and vehicle accessories are designed around 12 volts ( and some on 24 volts). But try finding a 48 volt phone charger or laptop charger! I know there are converters of course, but it adds even more cost. I think most people are well served sticking to a 12 volt system.
 

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Batteries can easily operate 20+hrs continuously, if not drained in those 20+hrs. I don't understand this thought if you'd like to explain further.

Discharge can occur at higher rates than the 20 hour, but if you notice the numbers on that battery reduce total capacity for faster discharge. 225 @ 20hr, 40ah is "lost" for the 5hr rate @ 185 (92.5 usable). The 75amp @ 115 mins would run it dry and ends up being only ~145ah. Voltage also drops during as the batteries drain, which will throw off back of the envelope calculation and can damage electronics
 

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I absolutely do not like your 3kw 12v inverter. I'm glad you sized wires correctly and don't actually utilize the 3kw. Our definition of "safe" must differ though. The 120v side of your inverter is safer to the human body than the 12v. Current will do more damage than voltage

Edit for clarification: this refers to a short circuit. The resistance of the body will "feel" a higher voltage whereas 12v will not "shock" under normal circumstances. I would much prefer shorting a 15a 120v circuit than 150a at 12v despite them being relatively similar power levels. Both will go "boom"
 

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Batteries can easily operate 20+hrs continuously, if not drained in those 20+hrs. I don't understand this thought if you'd like to explain further.

Discharge can occur at higher rates than the 20 hour, but if you notice the numbers on that battery reduce total capacity for faster discharge. 225 @ 20hr, 40ah is "lost" for the 5hr rate @ 185 (92.5 usable). The 75amp @ 115 mins would run it dry and ends up being only ~145ah. Voltage also drops during as the batteries drain, which will throw off back of the envelope calculation and can damage electronics
It鈥檚 simply about economics and limiting battery bank size and weight. You can add batteries so they can last 20 hours, but at what cost?
 

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1x 50ah battery could continuously power a LED bulb or computer fan with under .5ah draw for days. That same Trojan battery is rated for 100hr discharge. Limiting draw and upsizing batteries are roughly the same effect. Batteries don't have a natural limitation on how long (timewise) they can operate. It's based on capacity
 

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I've calculated our energy usage at ~229 amp hours per day . . .

The two main draws will be a NovaKool fridge/freezer and an induction cooktop. The induction cooktop will be our only (planned) use of an inverter . . .

Which brings me to my first question: When estimating power needs, do you actually assign a value to the inverter? Or do you figure some amount of loss from the DC -> AC conversion?
Wow - - 229 AHs . . . you're a man after our heart! Everyone on this Forum prides themselves on how few amp-hours they use . . . it's a game, like golf, the fewest 'strokes/number-of-AHs', wins. And in keeping with our 'golfing' analogy (and with the additional bit of information that the last time we kept our golf score, we scored a phenomenal 129 strokes), our goal would appear to be 'consume as many amp-hours' as possible. We commonly use between 200 - 350 AHs (at 13 volts)/day.

We, too, have a NovaCool frig and an induction cooktop. We also use a hot-pot for many of our 'hot water' needs (it is true that the cooktop boils water very well, but then we'd have to get a pan out). But these loads are all intermittent and, in the case of the stove and hotpot, of comparatively short duration. We doubt you'd ever use 229AHs for these appliances alone. But, you will discover that your needs will continue to rise over time as you add one little gadget after another. Consumption never goes down. So, our advice, 鈥渙ver-spec鈥 your needs. Retain that 229AH target.

A comment on inverters. There are actually two forms of inefficiency. The first is the one already mentioned in this Thread relating to the efficiency of converting 12 volt DC power to 120 volt AC power. The number suggested - - 85% - - is good.

But there鈥檚 a second efficiency which most, on this Forum, don鈥檛 worry about. That is the residual 鈥渋dling power鈥 consumed by an inverter, while on, with no loads on it. This efficiency is 0% - - all the energy consumed by the inverter while 鈥渙n鈥 but not supplying AC power to any loads is lost. It鈥檚 been awhile since we鈥檝e measured this number, but it will be several amps meaning several amp-hours/hour. Most, here, don鈥檛 worry about it because they religiously turn-off their inverters when not in use. We leave our 鈥榦n鈥 24/7.
 
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