Converting a heavy-duty bus/coach/truck into a motorhome (page 51 of 161)

What you're saying is true for 24V—less line loss and thinner cables. As for converting 24V to 12V, it's possible using a kind of transformer that's actually a switching power supply. Depending on the power rating of this "transformer," you can power 12V devices. However, to recharge a 200Ah battery at a reasonable speed, you’ll need at least 20A available, which is about 10% of the battery’s capacity. At that point, it’s better to install a 12V alternator, though 24V-to-12V voltage droppers do exist for this power level (around 150 €). In any case, **avoid at all costs** your idea of using a series resistor to drop the voltage. At this power level, your resistor basically becomes an electric heater. Sure, the system works—it was used for potentiometers back in the day because we didn’t know how to handle high currents like we do now with switching (like with living room halogen lamps). The problem is that you’re wasting the excess voltage by dissipating energy as heat. So you’re already losing half your production capacity, and on top of that, if you put the resistor in the living space, you’ll heat up the area. Not great for summer...

Thanks so much for your replies! 🙂 I’ll try to contact the DIRECCTE and Veritas to see what I can do, but if I can’t drill into the body or the floor of the 0303 (since it’s a lattice frame), that’ll be the end of it! I’ll have to choose another one. Such a shame, I really liked it😕

Hi there, and thanks for the info! I’ve reached out to Pandrée and am waiting for their response. As for the measurements of my FR1, here they are: From floor to ceiling: 200 cm From step to ceiling: 183 cm From step to under the storage compartments: 155 cm

I don’t know the exact model of the FR1—it’s one that was used to transport athlete delegations during the Albertville Olympics. Back then, it had a rear lounge area, but it’s since been converted. It’s from 1985, and the serial number is SFR 1106.2 Series VF6SFR11000000210.

See you soon!

jl Corouge

okay, I'm starting to get confused again!!!! I spent the afternoon on the phone with the DRIRE, Ivobus, Veritas, and AFNOR about drilling the chassis (what a great way to spend my vacation week!). The DRIRE tells me I just need the manufacturer's approval, so I call Ivobus, who says they only want a quick sketch of my layout to give their approval. That works perfectly for me, but I don’t want any nasty surprises during vehicle inspections. Anyway, here’s my question: DOES ALL THIS SOUND NORMAL TO YOU? How’s the manufacturer supposed to know how many holes I’ll drill and what size they’ll be with just a quick sketch? I’m still planning to pick up my 2,500 € Mercedes 0303 on Monday, but I’m hesitating—what do you think?

Okay, don’t hold it against me—I’m not picking on you, but I can’t leave folks in the dark. 😉

You’re reasoning wrong because short-term, sure, half the consumption but twice the batteries upfront—okay, but not in use. I don’t agree: half the discharge, longer lifespan, but for a camper van (CC), that’s not the real question. The REAL question is: AUTONOMY when parked. 🤪

Quick applied physics refresher (10 years since I left all that—gonna do me good, ah, nostalgia 😇)

Yep, electricity was my school training—BEP, CAP, vocational baccalaureate—and then my job, including 5 years in schools. Ah, the carefree days of tinkering, explosive experiments, and a steady paycheck at month’s end 😎—my youth... WHOA, I’m rambling, rambling—back to the topic! 😮

Grab a sheet of paper and a pencil, take notes: (couldn’t resist 😏)

For a pure resistor (incandescent lamp, absorption fridge, electric heater, basic coffee maker...), here’s the formula:

W (power in watts) = A (current in amps) × V (voltage in volts) → so far, so good. Industry also calls it volt-amps (VA).

If W = 100W V = 24V A = 4.17A (100/24) → still with me?

If W = 100W V = 12V A = 8.33A (100/12) → getting tedious, but still on board?

SO, TWICE the consumption! I stand by what I’ve written before—sorry about that.

If 1 12V battery at 200Ah: at 8.33A consumption, 24 hours of autonomy (200 / 8.33).

If 2 12V batteries in series (24V) but STILL 200Ah (in series, voltages add, currents stay the same—opposite in parallel), at 4.17A consumption, 47h58min of autonomy (47.96h).

So, nearly TWICE the autonomy (give or take 2 minutes). WARNING: Math time → twice the capacity with the same starting point means (no symbol, but here it is) → almost HALF the consumption.

Q.E.D. Thanks, thanks, my dear Watson—whew! Alright, everyone else: 4 hours, and you’ll copy this 10 times.

Just to hammer it home since this is the heavy-duty vehicle post: For 100W at 40,000V, you get 0.0025A (2.5mA—top notch!).

Oh, and here’s a BONUS: If you switch from 12V or 24V to 220V, do it ONLY for the bare essentials—there’s significant loss with inverters, and you’ll drain the batteries faster.

There you go, there you go—I’m giving advice, but I’m on 12V because I don’t need much power. Still, I don’t recommend it: I’ve already "fried" the bus’s two starter batteries because charging pulls from just one battery (I bought an expensive 24V/12V coupler/separator, but it’s actually just a basic 12V/12V one). So you’re drawing from one battery, the regulator/alternator charges at 24V between the two terminals (27V exactly), but since one battery is more discharged (because the coupler pulls from it, and weirdly, over time, the voltages don’t balance well???), you end up with one battery at 11.5V instead of 12.7V and the other at 13.9V instead of 12V—premature wear, why? How? 😕 Anyway, I’ve got two new ones now, so it’ll be better.

Sorry for the long theoretical lecture 🤪 GX47

hi, I thought the 0303 was the evolution of the 0302?

The 0302 has a chassis, a real 30 cm high one! I saw it up close, it's not a ... oh sorry.

So if it looks the same, try an 0302.

Anyway, as Patrick26 already mentioned, it's better not to cut a lattice frame.

To simplify a bit, the DRIRE (French industrial vehicle authority) accepts all modifications as long as you have the manufacturer's authorization. Before giving their approval, the manufacturer wants to know what you plan to do beforehand, which seems reasonable to me. I’d be very surprised if the manufacturer allowed you to cut into their lattice chassis, but you can probably make holes and openings in the sheet metal without touching the main structure. For example, in my case, SETRA allows me to lower the floor. For them, the part where you walk in the bus doesn’t contribute to its rigidity or strength, so I can lower the floor. Every manufacturer is different. Negotiate with them and, most importantly, provide them with a fairly precise plan—not just a rough draft. You’ll need to put together a dossier that inspires confidence if you want their approval.

Evening and thanks for this heated debate on the electric topic. 😛

I’m starting to see things more clearly. Logically, I’ll probably go with 24V. Is the power loss in 220V really that significant? Because I’ll definitely need 220V... Is it possible to calculate this loss? Thanks again for your replies.

Normally yes, but it's a real headache—you need to know the impedance, resonance, how the inverter is built, what components it uses... in short, a total pain! Back in my vocational school days, I was top of the class on this stuff, but now I'm completely lost, not even a clue, because I haven’t practiced or kept up (and I hate math and integrals 😡).

Don’t hesitate to set up 220V—it’s always useful. Normally, you can easily calculate the loss by subtracting (I’m not sure about the spelling) the delivered power from the consumption (the manufacturer should provide all that info).

Be careful not to run 220V through the same conduit as 24V (risk of impedance in the DC circuit (24V), residual current, and most importantly, different insulation). To avoid risks, only buy U1000 or U500 cable or wire (designed for 220V).

For the cross-section: 10A per mm². But the standards require 1.5mm² for 10A; 2.5mm² for 16A; 4mm² for 20A; 6mm² for 32A; and I’m blanking on 16 or 25 for 63A—ouch, I don’t remember 😕. Ugh, I feel useless 😅. I’m embarrassed now.

Anyway, 6mm² is already decent in a bus

No offense, but I think françois57 and you are right. I haven’t always been a police officer—I’m also a trained electrician.

Regarding current intensity, it’s true that even without your demonstration, it’s obvious we use half the current at 24 V compared to 12 V. However, when it comes to energy consumption, aside from minor savings on line losses or efficiency at 24 V versus 12 V, I think it’s the same. You halve the current but double the voltage, so for most camper van appliances with a power factor of 1, for 100 W: at 12 V: 8.33(A) x 12(V) = 100(W); at 24 V: 4.17(A) x 24(V) = 100(W).

Still, you’re right that at 24 V, you double the capacity—it’s true that switching to 24 V doubles the autonomy. The amp-hour (Ah) rating stays the same with two 12 V batteries in series, but since the current draw is halved, you effectively have twice the stored energy—even more due to reduced line losses and the battery discharge coefficient (C10, C20, C100). The less current you draw at once, the more the battery delivers.

Battery capacity varies depending on the discharge current. A key concept! Battery capacity is rated based on the discharge current. For example, a BSG68 is a battery whose 68 Ah capacity is measured by fully discharging it (which is strongly discouraged for its lifespan!) with a current equal to 1/100 of its capacity (0.68 A). This means, as clearly stated in the document, that the same battery discharged at 1/20 of its capacity (2.75 A) will only have a capacity of 55 Ah, and at C/10 (capacity over 10 hours), 50 Ah—so 5 A for ten hours. It’s obvious that with a current higher than 5 A, the capacity (in Ah) will be even lower! Similarly, you could imagine a discharge at C/500 (0.16 A), which would give a capacity around 80 or 85 Ah at C/500. That’s a very practical but also "very flexible" concept to keep in mind. No offense, but I think this little explanation complements yours.

You can easily find converters with 94% efficiency. I’ll post the documentation online if I manage to get it done for reference.

Hi there,

I’m new to posting here, but I’ve been reading this forum for several months now. I’ve been observing up until now and have taken in all the advice from everyone (though there’s some nonsense too ;)). Thanks, Patrick, for creating this forum.

If there’s a 2007 gathering, I’ll be there. I live in the north (59) between Douai and Valenciennes.

As for the FR1 windows, I didn’t touch them—I just degreased them with a strong solvent and painted them from the inside, then installed the partitions. So far, nothing’s moved. Maybe in a few years, I’ll have to redo it, and if so, I’ll do it from the outside. As for the aluminum rails on the side, I’d advise you not to remove them. I used them to secure the furniture, partitions, etc. If you want to know more about the FR1, you can call me at 06.80.43.49.96. You can also check out the state of mine here: http://fr15966.skyblog.com/

See you soon

SOME GREAT WORK!

I don’t have much time right now, but I’ll get back in touch with you!

Bravo!

PATRICK26

Hi and thanks for your message! I checked out your blog and found lots of interesting stuff. My first question is: has your bus been approved by the DRIRE?

Secondly, regarding the aluminum rails along the bottom of the windows—I think they carry hot air. From the photos, it looks like you’ve placed furniture in front of them. How did you handle that issue? There’s also mechanical ventilation at the top, which must now be inside your furniture. And at the top of the windows, there’s natural ventilation—probably to prevent condensation, right?

The fresh water tank you bought on eBay—is it partitioned?

Last question for this morning: what did you do with the overhead storage compartments, and do you think they’re standard? I’m thinking of looking for some myself.

See you soon, and thanks again! jl Corouge

When I see what you’ve done with your FR1 😉 you’re gonna make some people jealous and envious—the enthusiasts who just read the forum without signing up are gonna regret it. Getting known and sharing a passion, what could be better? Well done again and welcome among the crazy bunch.

Great job fr159 for the high-quality work, that lapse in taste aside. Such a nice fr1! By the way Patrick, when are you posting the weekend photos on the forum? See you soon.

For the weekend photos, I need to explain...

Caught up in the organization, I forgot my camera! So I asked the forum members who were there to send me the photos they took so I could compile them and post them online... and so far, I’ve only received ggdbdb65’s!

I’m waiting for the others and I’ll post them! Promise!

Anyway, I have some news:

Sébastien, my friend, my buddy, my partner in crime—those who were at the weekend met him, and others have been in touch through these plans—is joining this forum under the username "junior"!

His background in industrial design with a focus on space planning should interest many of you!

His strong point:

Analyzing needs and value (a fancy term I’ll explain simply)

When we were thinking about our needs for the camper van kitchen, I had a discussion with him. Should I get a 3- or 4-burner stove? An oven? A microwave? What size fridge? Freezer? etc...

And he, very pragmatic, answered: we need to do an analysis! Me: "How?" Him: "Forget all the material aspects and write down what you’ll eat in your camper van. Don’t think about how you’ll cook, keep things cold, reheat, etc. List breakfasts, lunches, snacks, and dinners for 3 weeks of vacation. Tell me if the meals are eaten in the camper van or outside (e.g., at a restaurant)."

Well, my wife and I made the list!

And together with "junior," we were able to determine what equipment was needed!

That’s what he calls "constructive constraints"! And by applying these methods, which improve the products and tools in our daily lives, he manages to determine the level of need coverage without excess, but most importantly, without gaps!

It works for seating space, bathroom size, storage volume, or the amount of water to carry!

He’ll be able to tell you the comfort dimensions for your benches, doors, work surfaces, etc...

Building a camper bus isn’t in his plans, but mine and yours amuse him! (Isn’t that right, famillede8, who spent 2 hours with him and left with his digital plans under your arm!)

Give him a warm welcome (he’s a bit shy😊...), and don’t hesitate to ask him questions. He won’t tell you what type of battery (or how many amps) to get, but he can help you study your daily needs, for example.

And now, a contributor live on the forum!

PATRICK26

We still haven’t gotten the photos yet (too bad)🙁, nor much info on how the days went. How many buses actually showed up, an estimate of visitors, the pros, the most impressive builds, the techniques, technologies—everything! Come on, PATRICK, we’re counting on you and anyone with info and photos.😉 fab

Okay, Patrick started introducing me (except "junior" is already taken)... So I’m jumping into your discussion, even though I’ve been following it for a while (since the first post). To balance things out, I’ll introduce myself...

I’m Patrick’s buddy and former business partner, so I know his project inside out since I was part of it (I still tend to refer to his bus as "our" bus). Some of you know me from meeting me during the weekend in Chabeuil, others because I’ve spoken to you on the phone. Your fit-out projects are awesome, and I’m tempted to join the adventure, but the only catch for me is that it’s the means, not the end goal, that excites me. In other words, for now, I don’t see myself living or going on vacation in a motorhome (but if I did, it’d be in a heavy-duty one). I’m an industrial designer by training (after a mechanical engineering DUT). To put it simply, forget that design means "pretty"... Design is about giving meaning and form, and above all, it’s about meeting a set of requirements. In other words, I apply creative thinking methodologies (sounds complicated, but it’s not) to address needs. For many of you, the challenges you face are seen as restrictive constraints. For me, constraints are sources of inspiration and the only real basis for decision-making. For those who want to live in their motorhome year-round, the real question is how you’ll live (what activities, how much time, how many people will share this activity...) and the answers you come up with will necessarily differ from someone who wants to go on a family vacation. So your fit-out and equipment solutions will be different. Similarly, it’s great to draw inspiration from solutions you’ve seen in other heavy-duty motorhomes or campers, but don’t forget that most are designed to meet the needs of the masses (mass production, rental) or needs that aren’t yours! Regarding Patrick’s bus, we went through about ten different layout plans, and like all of you, since it’s a prototype, it’s likely to be modified. These aren’t fabrication plans, by the way (for the purists, I did the plans in Adobe Illustrator, not in a technical software like AutoCAD).

That’s my first post—now you know I’m here, so if I can help... Good luck with your project, and don’t give up!

Hi Sébastien, and welcome to the club of crazy internet users.

I just want to say thanks again to you and Patrick26 for the amazing weekend you gave us.

See you soon, Patrick nahotchan...... and your wife.