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Overland truck electrics - 24V or 12V?
Hi all,
I am currently kitting out my MAN/VW 8.136 and completely redesigning the electrics. I want to keep the original truck circuits (24V) and add a separate installation for all other applications. I am considering using a separate 12V alternator to charge a bank of 12V batteries to power all ancilliaries (interior lights, fridges, heaters, chargers, multimedia, camping equipment, etc.) What are the pros and cons of using 12V rather than 24V for these applications? |
electrics
HI Roman
so most people who have a truck normally do extended trips so the 24v system for the front is good and the 12v for the back is also a good idea. but what sort of overlander are you, do you drive everyday and charge your batteries or sit in one place for a couple of weeks. solar panels for all electrics is better than a alternator, you will be surprised how many amps you can use. most rated amp kit tends to use more than the manufacturer says:nono: and sitting on a beach for 2 weeks starting your engine and having to charge your aux bats can take upto 6 hours. we have two sets of batterys in the back of our truck 24v charged off the engine for our invertor 12v solar for all other electrics fridge etc as we live in our truck the 24v comes in handy for a back up source of electric they say 24v is more efficient than 12v |
Hi Roman,
I'm not an expert on all the pro's and con's I'm afraid, but I do run a 24v aux battery bank in the back of my 24v Landcruiser. The ability to jump start myself if needed was my main logic, for this reason I use normal starter batteries for the aux bank, I'm too tight to splash out on super do-it-all gell ones and I never get to the point of drastically discharging them (don't run a fridge though). I do also believe that 24v is more efficient. The idea of using a second alternator is, in IMO, an excellent one. Combined with solar top up would be great too if you plan on staying in one spot for long. The only thing I've found with 24v is that some things have been expensive or hard to come by, where as a 12v version would have been easy/cheaper. It's all doable though. Another thought, if you are mounting a second alternator, it may be good to know it was a direct swap for your original one if you ever needed it in a remote spot. This factor along with the jump start ability would swing it for me, but some aux kit maybe a bit more expensive. Sorry that all got a bit rambly! Happy travels & enjoy the MAN Sam |
voltage drop is a fixed equation dependant on the cross sectional area of the cable used so a 24 volt system will suffer less relative volatge drop over a run of a given length and cable size compared to 12v. this doesn't matter in cars but can be significant in the relatively long cable runs trucks can have.
setting up your solar to charge a 24v rather than 12v is relatively simple. If you connect your panels in series then the voltages will be added together while the amps remains the same. so, if for example you had 2 panels each producing 12v and 50amps then you connected them in series that would give 24v and 50amps, or 1200w. If on the other hand you connected them in parallel that would produce 12v and 100amps, also 1200w. the difference would be that on a long run the 12v installation would lose a higher proportion voltage so dropping the effective power. as an aside, amps are affected by shade, volts aren't. if part of your panel is shade you will drop the amperage of the WHOLE installation. connecting several panels in parallel reduces the tendancy to drop the whole output down to the value of the poorest performing panel. the other way round this is to make sure your panels have bypass diodes fitted. bit wordy but I hope that helps!! |
Thanks, guys, for your replies.
I am aware of the electrical properties of 12V vs 24V installations. What I was courious to find out was how the two compare in real life situations, particularly in terms of reliability and vis a vis different types of equipment used in different envoronments. What if something breaks down? Can it be easily replaced knowing that 24V goodies are not popular outside the trucking market, which in 3W countries is not quite like in Europe? Certainly, a 24V setup with a 12V step down converter is an option, but will it be less wasteful than a long cable run using a 12V wiring? I am aiming at a decent solar power supply for prolonged use when stationary. Now, considering reliability would I be better off using solar panels connected in series and feeding a bank of leisure batteries (also conected in series for 24V output) or a parallel 12V installation? As Moggy said, the series setup is as good as the poorest performing panel/battery. What is the typical current consumption you have experienced using standard motorhome devices and operating lights, heaters, fridges, pumps, electronics, recharging laptops, etc? I.e. how much amp/hour capacity should I have and what will be the solar panel output to match? |
sorry Roman, wasn't trying to teach you to suck eggs, I know your extensive background from your other posts but not everyone reading is in the same position.
if you have a voltage dropper close to where your 12v demand starts then you will minimise the effects of voltage drop. I believe they are quite expensive but you could probably get one from a landcruiser. my H60 has one for the towing electrics which is behind the panels in the side of the boot space, I think on the right hand side, but don't quote me on that, or maybe it's the left:(. I believe there is a second one for the radio. otherwise I would imagine truck parts shops do them so truckers can fit standard stereos. I would imagine truck accessories in 24v would be more durable than their 12v equivalents simply because they are built for a commercial environment. this may not apply to marine quality 12v stuff such as lights etc. Even in the 3rd world the lorries will be 24v so availability of basic parts (bulbs etc) shouldn't be a problem. I am sure many of the big commercial motor homes and boats are 24v with 12v accessories and I would guess there's a good reason. It may be nothing more than a wider choice of accessories. reading that back you may think I am undecided which is best. thats because I am! it's a good point for discussion as it's far from black and white |
Voltage droppers are expensive if you require a high ampage.
I have bought a 20amp dropper for my truck, made by durite (ie good quality)......got it on ebay for 10pounds. Brand new they can go for ABOUT 70 Pounds. Suggest look for one on Ebay, there are lots available. I use mine to run the stereo and a 3 way charge point so 20amps is a bit excessive for just this, but it was a bargain. |
Go thru what you are going to run
24 volt laptop supplies - not sure , often preferred to using invertors Fridges - most of the decent fridges work on 12 or 24 volts Diesel heaters (ebers etc) are actually cheaper in 24 volt versions 2nd hand Lighting - should be doable in 24 Volt Pumps for water etc - sureflo is available in 24 volts So maybe better to keep 24 volt system through all the system then you can se the batteries in an emergency as a starting system |
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I bought some LEDs from here
http://www.bedazzled.uk.com/Download...n_for_LEDs.pdf The first two I bought from a UK supplier on Ebay both blew, one straight away! At £10 a pop roughly thats not too good. I wouldn't have more than a couple of general illumination LEDs though, with halogens for "work lighting". Both lots I bought are something like 10-30 volts. The Vitrifrigo compressor fridge, which has a danfoss compressor, draws about 3 amps at 24v and runs about a third of the time. It will also run on 12v. Sterling do battery to battery and alternator to battery chargers, which will all charge more quickly (and I think more fully) than an alternator. Sterling Power Products: Alternator to Battery Charger If that helps. Jason :) |
another place for info as a few people run 24 volt trucks is the self build motor caravan club (sbmcc.co.uk), very helpfull folk
I'd keep away from halogen for internal fittings and go led - halogens use far too much power, i've swapped all my internal lighting for led and it now uses less power than 1 of the halogen bulbs that were there previously. |
Just a note on the 24 - 12v droppers......
They (or mine at least) draw current even when there is no load on them/it. I've had to fit a correctly rated switch to the 24v input on mine to stop it trashing the batteries if I leave the truck laid up for a while. I haven't measured it and I don't suppost it draws massive amounts, but something to be aware of (or maybe mine's just crap??). The only thing i've had trouble with in 24v has been the stereo, everything else i use goes direct 24v (interior lights, diesel transfer pump, water pump, laptop charger, gps, inverter etc etc.) The only thing I've ever needed an inverter for has been charging AA batteries (if anyoine knows a 24v answer to this, please let me know) |
^ Agreed with the constant draw a dropper takes from the batteries.
But if my truck is laid up for anything more than 3 days, I have a battery master switch/isolater that breaks the main negative, so nothing works. You can get decent ones capable of high ampage for around 15quid. Also good for when you're doing electrical work generally, and as an extra element of security (though a really determined thief will quickly figure it out) |
not sure the 'cruiser has a problem with that. the batteries do go flat eventually, but it takes a few weeks.
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Quote:
As inverters are quite pricey, I did the following for charging AA batteries. The exisiting 24v cigarette/charge point....I ran the exisiting 24v fused wire into a 10 amp voltage dropper (24v to 12v), then the output 12v from the dropper to the cigarette charge point. Then got a 3 way charge point that plugs into the exisiting cigarette/charge point (about 4 quid on ebay) I have run a GPS, recharged AA batteries, and charged an mp3 player all off this via the 10 amp dropper at the same time, no worries........but only with the engine running...I never charge when engine is off as before now, I never had a split battery system, everything was off the cranking batteries. I am changing that now to a split system. Doing it this way takes a while longer to charge than via an inverter, but a cheaper alternative to inverters. |
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