benr8440667 Posted February 28, 2018 Share Posted February 28, 2018 Good afternoon gents... I would appreciate any comments on my wiring plans as there are some things that i cant work out and generally would like some input into weather my plans are viable. Forgive me if this goes on for a while!... I have wired up a large inverter (2000w but i wont be using a load over 1kw- i bought a larger inverter for startup surge and futureproofing) to my habitation battery bank (2x100ah) All seemed well and it seems to work fine. However it has been brought to my attention by some expertise on this forum (Allan of aandncaravan) that its not a good idea to wire it up in this way as if i run the engine whilst drawing large inverter loads then the alternator will try and supply the inverter massive amps through wiring and pcbs in the motorhome that arent up to it and probably melt stuff. My plan was to run the engine whilst using large ac appliances much like having a generator, but it seems i cant do this. The advice seems to be to wire the inverter to the engine start battery instead. My problem with doing this is that I need to run small ac loads from the inverter constantly whilst off EHU (extra fridge/ extra freezer/etc- got three kids under 4!) And I will end up flattening the engine battery in no time. When i found out that i couldnt do this after all my initial instinct was to add a couple more batteries to my habitation battery bank. However. Having read through Allans website guidance section it seems that I will have another situation where I will melt bits of the motorhome due to the amount of current required to charge the increased battery bank. Mmmmmm tricky.... So now my plan is as follows: I would like to run additional cables from the inverter to the engine battery with a 200a relay on the positive which will open when the engine starts via ignition live to supply the inverter when the alternator (120a) is spinning. At the same time I will use another relay switched by ignition live to disconnect the positive wire on the cables between the habitation batteries and the inverter whilst the alternator is spinning to prevent the afore mentioned dangerously large draw through the vehicles factory wiring. I think that this should give me the best of both setups. i.e. i can use the engine and inverter like a generator for large ac appliances. And with the engine off use my habitation batteries to supply the inverter for constant small ac loads without flattening my engine start battery. In conjunction with this i was thinking i could use a seperate relay to disconnect the alternator from charging the habitation batteries whilst the engine is running to supply the inverter, in order to allow maximum alternator amps for the inverter and avoid overstressing the alternator. I was thinking i could do this with a relay switched by the ac out supply from the inverter. However no matter how much i google it, i cant find a relay that can switch 12vdc with a 230vac supply. Any ideas on this anyone?? I can see that a stand alone generator seems a far easier sollution to all of this (or staying at home!) but even ‘silent’ gennies are just too noisy for us. Does all of this sound like it will work or am i missing some important factors?? Thanks for bearing with me and any comments or ideas will be gratefully received. Hope everyone is enjoying the snow! Kind regards, Ben. Link to comment Share on other sites More sharing options...
Tracker Posted February 28, 2018 Share Posted February 28, 2018 My problem with doing this is that I need to run small ac loads from the inverter constantly whilst off EHU (extra fridge/ extra freezer/etc- got three kids under 4!) And I will end up flattening the engine battery in no time. Assuming leaving the kids behind is not an option, what is wrong with running the fridge and freezer on gas which is what it should be designed to do? We never had freezers in any van, other than a tiny compartment in the fridge, so we got used to shopping regularly as part of the holiday and I guess with kids you will never be that far from shops? Link to comment Share on other sites More sharing options...
benr8440667 Posted February 28, 2018 Author Share Posted February 28, 2018 Hi Rich, thanks for reading my post. I’m all for leaving the kids at home but the wife just wont go for it! We have the built in 3-way fridge freezer but find that we need an additional fridge and an additional freezer in a compartment underneath (big motorhome/portacabin!) i bought domestic under-counter versions of these as 12v or gas versions were out of my league price wise. We like to go off the beaten track a bit away from shops, and dont really eat out so we carry a load of fresh and frozen food. It would be easier with tinned stuff and the gas hob i know. Thats just how we operate and so thats why i have embarked on this route. Its also quick and easy to boil the kettle and microwave food whilst travelling. Shame affordable gennies are so loud... Link to comment Share on other sites More sharing options...
Tracker Posted February 28, 2018 Share Posted February 28, 2018 Fair enough, I didn't appreciate the add on refrigeration was mains only. Ain't the simple things in life complicated these days! Link to comment Share on other sites More sharing options...
tonyg3nwl Posted February 28, 2018 Share Posted February 28, 2018 Hi, firstly , engine or not, what is the alternator rating, max current output. Even when engine is not driving vehicle, it sound to me as if the alternator rating might not be man enough to drive a fully loaded inverter. 1 kw from 12 volts is a heck of a lot of current. 1000/12 amps which is close to 100 amps. That amount of current requires some very hefty cable size to avoid cable resistance losses. A resistance of 1 ohm, passing that much current, dissipates lots of watts. Ie heat. I squared x resistance . that sounds like electric fire.and that is before any invertor losses in stepping the voltage up to mains voltage for fridge etc. my arithmetic may be faulty, but my advice is that you are mad to consider it., let alone the complexity of relays to switch things around. if you insist on having a requirement for mains power, then my only suggestion is buy a decent generator. DONT MESS WITH ELECTRICS, IT COULD QUITE EASILY CAUSE A MAJOR DISASTER, FIRE, OR KILL YOU. Tonyg3nwl Link to comment Share on other sites More sharing options...
Keithl Posted February 28, 2018 Share Posted February 28, 2018 Sorry Ben but I have to agree with Tony, far far tooooo complicated and the risk of things going wrong doesn't bear thinking about! For example, relays don't open or close instantly, they have an inherent delay. So as one failure mode you could possibly end up drawing starter motor current from your leisure batteries if it doesn't work as you expected. Secondly don't bother with 12 volts for heating. As Tony has said 1 kW will take well over 100 Amps allowing for inefficiencies. That's why most MH's have gas on board. Ditch the leccy kettle and get a good one to go on the gas hob. If you really are adamant to go ahead with inverter's then the only possible solution I can suggest is to get a smaller inverter wired to your leisure batteries to run your fridge/freezer, etc. and then wire your 2,000 Watt jobbie direct to your starter battery and possibly double up your starter battery to cope with the load. Basically run two entirely separate inverter systems. A possibility but one I personally would never venture to try!!! Keith. PS And you will have to add an isolator switch to the 12 volt feed to the inverter or its quiescent draw will flatten your battery(ies) pretty quickly! Link to comment Share on other sites More sharing options...
Tracker Posted February 28, 2018 Share Posted February 28, 2018 Weldted's solution seems to work well? http://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Technical-Alternator-or-Inverter-charging-/48365/31/#M556701 Link to comment Share on other sites More sharing options...
aandncaravan Posted February 28, 2018 Share Posted February 28, 2018 Ben, I think you need to step back a little as I think you might be a bit to optimistic about, "the small continuous AC loads", because they are actually significant loads. A small Motorhome Absorbtion Fridge running on 12v will draw about 10 amps pretty much continually. That will discharge a 100AH battery in just 5 hours, assuming you follow normal advice not to drop a battery to greater than 50% DOD. That is why Motorhomes run Fridges on Gas when no 230v is available. If you also have a Freezer of the same size (you seem to be talking about 2 separate additional items?) it would probably use the same sort of current, giving your two 100Ah batteries a life of 5 hours, before you even start to take lights and TV consumption into account. I know your 'extra Fridge and Freezer' are domestic 'under the counter' compressor versions and will use less current, but they still use a sizeable amount from the habitation batteries/Inverter. In your case you must also factor in a minimum 20% additional loss as no Inverter is 100% efficient. Some can be as poor as 70%. Add in the power taken by lights, TV, iPad, computer, phone charging, water pump, etc and that is big amps being drawn every hour. Add on a Microwaves 100amps for 15 minutes and you have serious battery drain issues. That will grow to be Mega issues if cooking for 6 takes 30 minutes of the microwaves time? 700watt Micros tend to be slow 'cookers', requiring longer running times. I have no idea what your total daily draw is, but as an example drawing an average 10 amps/12v for 24 hours is obviously 240AH a day requiring a 580 - 600Ah battery bank at the recommended 50% DOD. You need to work out exactly what your load will be and size the battery bank accordingly. Suggest you also need to work out if you can put all that energy back each day? Recharging a battery bank to put back 240Ah a day is one heck of a challenge without 230v mains EHU. Remember that when calculating recharging current required that no battery is 100% efficient, so you might need to put in 120Ah to get out 100Ah. Therefore if you are recharging the batteries from Solar, allow 20% more Solar harvesting than you are using each day in mid Summer and that in Winter a 100w Solar Panel will average just 4Ah a day. Suggest you also check you can live with the noise of a domestic compressor Fridge and Freezer, as some can sound like a Diesel engine in the quietness of the night? Link to comment Share on other sites More sharing options...
benr8440667 Posted February 28, 2018 Author Share Posted February 28, 2018 Many thanks to you guys for giving me some feedback. Its very interesting to get some different perspectives on my ideas. I am no electrician (obviously) and so its great to get constructive critiscism on my plans before i proceed and waste time and money and potentially cause myself more problems. I take all of your points on board. I agree with Tonys point about a generator being a better sollution but we listened to various silent suitcase versions running (inc hondas) and they are still to noisy to use in some environments. Whereas running my motorhome engine is relativley quiet in comparison. I agree with you all that my idea does seem too complicated. And Keith, thanks for your idea to use a smaller inverter from my habitation batteries to power my extra fridge and freezer. And then wire my big inverter to the engine battery, mabe adding another engine battery too. That does seem a far more simple sollution than my ideas to use relays, etc. And as you say, I am not really aware of all the various pitfalls potential priblems i may have. Your new idea is better and I may well go down that route instead. Tony, My inverter is rated at 120amps by the way. And I am aware of the massive cables involved. I wired my inverter to my hab battery using 50mm2 cables, and the longer run to my engine battery will require 70mm2 cables (Going by the inverter installation manual) Regards, Ben. Link to comment Share on other sites More sharing options...
benr8440667 Posted February 28, 2018 Author Share Posted February 28, 2018 Thanks for your input Allan. As you say, I need to take a step back l. l will take some time to absorb all that you have said and have a good think about my exact requirements and what is best now that i am armed with all this new advice and information. Regards, Ben. Link to comment Share on other sites More sharing options...
tonyg3nwl Posted March 1, 2018 Share Posted March 1, 2018 Hi again, I query what is the difference between running a "silent generator" and running the diesel engine on the van to drive the alternator, to power your intended system, . a decent generator will give you 240 volts ac mains equivalent which you can plug straight in to your normalmains hookup position, and know that your proper mains/battery on board system unmodified at great complication, will serve your purpose without excessive hazards and unknowns You can easily provide a noise reduction enclosure for the generator, and position it in a suitable position onsite that would cause minimal disturbance to your neighbours. Even if you go down your multi battery , complexity of wiring and control switching etc, what about the extra weight of multi batteries,. I guess more than weight of generator, and where do you fit extra batteries. furthermore, what about insurance..I would suspect that no insurance company would cover you when you declare all the mods to the electrics that you propose. And heaven forbid that you were to have a disastrous fire as a result of something as yet unforseen, .Failingto declare them would inevitably provoke a refusal to pay out by insurers. think again please..DONT MESS WITH ELECTRICS. TONYG3NWL Link to comment Share on other sites More sharing options...
benr8440667 Posted March 1, 2018 Author Share Posted March 1, 2018 Tony, thanks again for your input. Can I please give you my reasons for favouring an inverter setup vs a generator setup. Firstly I think that a well silenced and soundproofed generator, built into a motorhome and fully intergrated into the vehicles electrical system RV style would be great. However the amount of expense required to achieve this is too great for me (i.e. A Telair type model bolted underneath the chassis would be great but these cost thousands.) This type of generator setup is a completley different kettle of fish compared to a suitcase generator where you have to park up, get it out of your storage compartment, plug it in, start it up, and then put it all away again, etc. I know that my inverter setup needs altering in order to make it better and more sustainable for the non-EHU stop offs. But nonetheless, with my inverter setup I am able to simply flick a switch inside the motorhome and turn the microwave (or anything else) on at any time. This simplicity of operation i feel, is worth some effort to achieve. I dont have to carry petrol. Additionally inverters are silent when running off batteries and my motorhome engine is a lot quieter that a ‘silent’ suitcase generator. I have listened to a few, including a honda EU 2.0 and they are a lot noisier. i think its the higher pitch of the petrol note that cuts through. Vs a low pitched diesel note, clad in motorhome body. Building an enclosure to sit a generator in whilst onsite makes it hassle when you are moving around every day or two as we tend to do. Regarding using extra batteries and replacing the amps drawn by our usage, well this is something i need to get to the bottom of. space for batteries is no issue as we have a very big motorhome. Whatever happens, I will ensure that however i do it, My setup will be safe, this is the reason I am posting my ideas on the forum so that experienced people will hopefully point out to me better and safer ways of doing things. By the way, thanks for mentioning the insurance factor- i believe my insurance company will cover having an inverter on board but i will check with them tomorrow. And I obviously appreciate that they wouldnt be happy with a non-safe installation that caused a fire. Interestingly I have now found out that I could buy a 4 position manual battery change over/ isolator switch. This is specifically designed to safely switch between two battery banks. Albeit manually. I am going to look at weather this would be a good option for my purposes. Regards, Ben Link to comment Share on other sites More sharing options...
sshortcircuit Posted March 1, 2018 Share Posted March 1, 2018 I hope you have a set of jump leads as sometime I think you are going to need them. Link to comment Share on other sites More sharing options...
benr8440667 Posted March 1, 2018 Author Share Posted March 1, 2018 Mabe you are right. Actually we are planning on coming up your way this summer for a month long tour up to, and around Scotland. If my batteries end up flat somewhere near Fife then perhaps you would be kind enough to give me a jump start?! I’ll make sure I pack the jump leads! Link to comment Share on other sites More sharing options...
sshortcircuit Posted March 2, 2018 Share Posted March 2, 2018 Part of my rescue kit is a set of jump leads and only used once so far. Parked up in aires in Valladolid and German in adjacent MH had a dead battery and was unable to get a replacement as it was Easter. We both had leads so it was an easy start. I hope you enjoy your visit to Scotland and do not need a jump start. Will be heading to Spain for a few months shortly. Link to comment Share on other sites More sharing options...
benr8440667 Posted March 2, 2018 Author Share Posted March 2, 2018 I must say I’m impressed with how far reaching your touring holidays are- Proper adventures! Spain, that will be great to head somewhere that you know is goin to be warm and sunny! We havent been brave enough to take our motorhome abroad yet. Scotland seems exciting to us. Looking forward to the scottish wild camping laws! Actually I have a question for you about midges. Will it cause us a problem? My wife has been reading about them and is a bit concearned they may spoil our holiday... Regards, Ben Link to comment Share on other sites More sharing options...
sshortcircuit Posted March 2, 2018 Share Posted March 2, 2018 The west coast appears to have the midgy problems and you will find many witches brews to avoid. Not had the midgy problems on the east coast. You are so near you need to venture across into France at least where you will find so many opportunities for camping, you will also find the roads are very quiet and easy to drive. Enjoy your visit up north as again there are some really nice spots. Link to comment Share on other sites More sharing options...
benr8440667 Posted March 3, 2018 Author Share Posted March 3, 2018 Hello again gents. Forgetting for a moment the important factor of how to replace the consumed amps from my batteries. Does this setup sound like it will work?? This is a much simpler setup idea than my initial idea, Using a boat world derived manual battery isolator/changeover switch. I propose the following method of switching between inverter power sources(dual battery bank setup): A four position battery change-over switch. Position 1 habitation batteries/position 2 engine battery/off/both. ***both position will parallel all batteries and allow the built in inverter charger to charge all batteries simultaneously if required (on ehu) . This will also allow emergency engine starting from the habiation batteries. Position 2 will also allow the inverter charger to charge the engine battery if required(on ehu) Position 1 will also allow the alternator to charge the habitation batteries via hefty cable if required I will wire the habitation battery bank, engine battery and inverter dc negative terminals, all together. The battery bank to power the inverter will be selected by the battery selection switch. This will have inputs from each battery bank positive terminal and one output connected to the inverter positive dc terminal. I will need to use one 12vdc relay (normally closed) to stop the alternator charging the habitation batteries whilst the engine is on and the inverter is in use- primarily to stop any big current draw from alternator to inverter, via the ‘delicate’ motorhome factory wiring/charging system. I will wire the relay coil to the inverter feed on the changeover switch. The relay, will break the circuit between alternator and habitation batteries when the inverter is getting a dc supply. I will put circuit breakers/fuses in all positive lines added. I will use 70mm2 and 50mm2 cables for the inverter dc wiring, as specified in my inverter installation manual (depending on lengths) I would greatly appreciate any electrically minded peoples input as to weather my idea is flawed? Kind regards, Ben. Link to comment Share on other sites More sharing options...
aandncaravan Posted March 5, 2018 Share Posted March 5, 2018 I would just like to highlight the actual battery capacity will be less than the label capacity if you are drawing large currents for the microwave, etc. As an example if you draw 190A from a 95Ah battery and drain it to 100% DOD (obviously a battery is best kept above 50%) the battery will last 0.3 hours and delivery about 57Ah, not the 95Ah you might expect. However if the power draw is just 9 amps, then a 95Ah battery will last just over 10 hours, delivering almost the full 95Ah when discharged to 100% DOD. We therefore suggest that if you intend to draw large currents you may find that the battery bank is effectively 20% 'smaller' than it's apparent rating, so maybe expect it to go flat sooner than calculations predict? You will find more examples in a battery discharge chart for a Varta LA95 on the Inverter webpage : http://www.aandncaravanservices.co.uk/inverters.php Link to comment Share on other sites More sharing options...
benr8440667 Posted March 5, 2018 Author Share Posted March 5, 2018 Hi Allan. I appreciate you giving me lots of good information. I agree with you respect of all that you say. It deffinatley isnt going to be feasable to run a massive inverter from my batteries for long atall. I do however want to wire my inverter to my engine batteries only for very occasional use of the microwave and, for very short periods. I calculate my microwave will cause the inverter to draw 85 amps. this will be for a couple of minutes very occasionally and with the engine running. I have decided that I will only run one under counter ac freezer from the habitation batteries when off ehu. This is very quiet and efficient. Also it hardly ever runs once it is all frozen. We will probably be on a campsite with ehu every other day too. And try to mainly use gas for everything when off ehu. Would you please give me your opinion as to weather the above wiring scheme will work to run my inverter on a battery bank selector switch? Thanks again. Regards, Ben. Link to comment Share on other sites More sharing options...
benr8440667 Posted March 6, 2018 Author Share Posted March 6, 2018 ... I have some more specific information for my intended power consumption when off ehu: Whilst using the inverter on the habitation batteries (200ah): -freezer 50w, but im not sure if this factors in the compressor start surge? (4amps inverter draw) Also the compressor only runs occasionally (150kwh per annum) -evening use of tv and sky box. combined wattage 57w (5amp inverter draw) On engine battery inverter feed, the microwave wil get occational brief use. But I was slighly wrong about my 700w microwave- it is rated at 1150w input. this gives an inverter draw of 96 amps. My alternator is rated at 120amps. Im intending to only use it when there is no other load on the engine battery. I am hoping to avoid needng a fast idle throttle setting? Additionally I intend to put 300w of solar on the roof to help charge the habitation batteries. Thanks in advance for any input. Regards, Ben. Link to comment Share on other sites More sharing options...
aandncaravan Posted March 6, 2018 Share Posted March 6, 2018 I know your description is quite detailed, but it doesn't show how it will be physically wired, without which it is hard to see what you are trying to do. A wiring diagram beats a hundred words? I am guessing your Motorhome is from around 2004, so maybe it doesn't have the complex electronics installed on later vehicles? If so, it probably won't cause any issues to bypass the existing Split charging? I wonder if your best approach might be to wire the Inverter from the habitation batteries, but to prevent any wiring/controller overload issues, run a separate Split Charge system from the Alternator to the habitation battery using a 200amp relay and fat cables. Your new proposal to reduce 230/12v consumption is good but the 96amps estimate for the microwave is only the 230v equivalent draw, remember few Inverters will be 100% efficient. Suggest you allow at least a 30% extra in your 12v draw calculations. for Inverter losses and the 'lost battery capacity' due to larger current draws. 30% on your 96amp creates a very different almost 130amp load on the battery bank/Alternator. I can't imagine any Motorhome Alternator producing even 25% of it's output at idle? Even at a fast idle it probably won't get near 60amps? You can uprate the Alternator and also fit a smaller pulley, so that more electrical power is developed at lower revs, but not sure how successful that will be? A 300watt Solar setup has the potential of charging at about 18amps in mid June over a 15 hour Solar day that runs from about 05:00 to 20:00, so up to 250Ah daily potential. However, in December you are likely to get less than 16Ah a day from around 3amps an hour for the Solar day of 4 hours from 10:00 till 14:00? So while Solar is a way of putting back the power in June, the generation capability slowly drops off as you move towards Autumn/Winter. You can see that adding an Inverter, extra batteries, Split charging, Solar, etc is not only expensive and time consuming but it's only a partial solution if you want to get out and about in Autumn/Spring. Using a quiet Honda Eu10i (nearly 3 times quieter than a EU20i) with Rain hood is not only a complete all year round solution, but it's cheaper, simpler and goes with you to your next vehicle. Depreciation is low, whereas the depreciation on the planned investment will be nearer 100%. Hence why someone suggested a generator as a solution to a vehicle with high 230v loadings. A generator matched with a good 12v charger solution can bring 200Ah of batteries back to full charge in about 3 hours. That isn't a lot of running time so the running costs are usually less than the cost of regularly replacing the batteries degraded under the load of an Inverter. You can choose the time you want to run the generator for 3 hours a day, like when neighbours are away, it doesn't need to run 24/7. Three batteries replaced every 2 years at a cost of £300 buys an awful lot of Generator petrol. If you factor in the 130a load on the 120a Alternator and it's potential replacement cost every 5 years, then a generator is loads less money to run in every way. Link to comment Share on other sites More sharing options...
benr8440667 Posted March 6, 2018 Author Share Posted March 6, 2018 Hi Allan. Huge thanks once again, for giving such a detailed and well thought out post. Its extremley helpful to my decision making. It cannot be disputed that for my purposes, a generator seems the best option in many ways. The facts have totally been hammered home. How I will proceed is still unsure i suppose. Whatever I do it will be influenced by all of the good advice and information that I have recieved on this forum. I’m sure everyone will be relieved to hear that I wont bore you further with any more posts on this thread as I think Ive exhausted it! thanks to all for bearing with me. Regards, Ben. Link to comment Share on other sites More sharing options...
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