12v batteries series vs parallel circuits,nissan altima car battery dead,laptop battery drains when off - Review

04.03.2015
This is the second (and final) part of my introduction to basic electrical theory – for owners of motorhomes and caravans.  In this section we will look at watts (and we all know that solar panels are rated in watts) and also the connection of batteries in both series and parallel. Amp = unit of measurement of the rate of electrical current flow in a conductor (much like measuring the flow of water in a hose).
Ohm = unit of measurement of a conductors ability to resist current flow (like measuring the resistance that a partly closed tap excerpts on the flow of water in a hose). Think of it this way … Say you had that 10,000 litre tank filled with water and you had a wide open valve going to a fire hose and you decided to have some fun and point the hose at all your mates standing 2 metres in front of you. I really doubt you could knock ya mates over with the stream of water from a garden hose and after a few seconds of drenching them, you would be dropping that hose and running away from some wet and angry friends.
So horsepower is just another way of measuring work done – just as you can measure weight in either kilos or pounds. OK, so watts represents power (work over time) and to get lots of watts you need lots of volts AND lots of amps. This is an important concept to understand when it pertains to the performance of your electric fridge, pump, light or even your power tools.
In a commercial wattmeter, volts and amps are measured and simply multiplied automatically for you. The hour part of the amp hour rating is simply that, its how many amps a fully charged battery can provide for a solid one hour.
Well, that battery would supply 50 amps now for 2 hours since it is flowing out only half as much as before. Three similar batteries in parallel are triple and so on… Usually this is done for cost, availability, space or handling reasons (just try lifting a 1000ah battery). Now suppose you stacked one big water tank on top of the other and connected them together. In the case of motorhomes and caravans, batteries are connected in series to get the desired system voltage. It is also common (particularly in very large motorhomes) to use a combination of series and parallel to create banks of batteries that are then connected together to give a very large capacity.
Here is the full version of Ohms law in the format that I used when I was learning it as an apprentice electrician. I am 69 and have never ever understood electricity with its watts and amps and volts, I just know that I would not ever want to be without it for very long. I tend to agree with your thoughts on adding a full system rather than dealing with something that may or may not have been done right. The only issue may be that if the motorhome has not ever been used away from 240v – it is very likely to have appliances that are not well suited to being powered from solar.
If the reason for wanting solar in your motorhome is to allow for free camping – I suggest having a look at my article on setting up a motorhome for free camping. Hi Gavin thanks for your rapid response and thanks for pointing out the 24v system I read one of your articles that mentioned you where having trouble with your 12v lighting did you sort that out? The aircon currents you are quoting are at 240v – when brought down to 24v you have to multiply this current rating by 10 (or 20 if you decide to go with 12v).
To use 24v you either need to install panels in pairs OR use 24v panels (which tend to be a little cheaper than 12v ones).
3 way 180 L seperate fridge freezer, 900 w micro wave, an aray of 12v lighting, smallish 240 v LCD TV, a couple of laptops & mobile phones.
For a week now I have been scouring the internet to get some understanding on how the battery & solar panels equate. We are planning to head west, in the near future, & what to make the most of the solar power sytem. Look forward to reading your other blogs to gain a futher insite as how to best utalise & improve the quality of our travels.
Connecting a second set of regulated panels to the caravan is ok – but not the best solution. Assuming you have the capacity on the caravan regulator – The best option would be to bypass the inbuilt regulator on the portable panels and connect them via the caravan regulator. This could be done by having two connections on the portable panels – one that is regulated (for use in the vehicle) and the other that is unregulated for connecting to the caravan regulator (of course you would only use one connection at a time). WE are only 2 months into setting up our van for free camping when I stumbled across your site.


Just to let you know of a new way of escaping the high prices of DC refrigeration I have just installed a new Samsung 320 Ltre 240 volt Digital Compressor Fridge Freezer in our motorhome.
I have Plenty of Solar and storage so its ok for me to go this way but I’m thinking this may be the best way for most large Rigs. I was wondering, My Fiat van has a 12v system with too much electronics to even consider changing. As a rule of thumb, the closer an inverter is to its full load capacity, the higher its efficiency. Re 1 I was considering your reply to have a manual switch, or should I simply just use the abilities of the dual battery system?
In my setup the auxiliary batteries (weighing up to 240 kg) should be best fitted over the rear axle.
The only alternative option is to position the batteries behind the driver, a distance of around one metre, but this will mean putting lots of weight on one side of the vehicle and impacting the design somewhat. Cable sizes I am acquiring about is for 12V, say 4 to 5 metres vs around 1 metre for the current coming from the dual battery system via the alternator. Regarding the fuse, I would suggest a self-resetting circuit breaker of a value around 60% of the rating of the alternator if the alternator is not hot rated. Step 1: Part 1 - Gather partsThis instructible can be followed to the letter, or changed to suit your own needs if you wish to use other batteries etc.
Step 5: Wiring in the relayThis is the part that may become confusing, so I would REALY recommend watching the video as mis-wiring mains electricity would be dangerous. Step 6: Final connectionsOnce you have checked, double checked, and triple checked all of your connections, you are now ready to wire your output to your socket.
Step 10: CCTV softwareI am having real trouble finding some decent free CCTV software so this page will be updated when I do! When homes have an alarm system installed it usually contains a backup battery in case of power failure. Would like to know more about what you have as front motor and controller for front wheel.. I was confused by some parts of your diagram, such as where to tap the battery and the relay switch and the booster switch. Lots of volts (pressure) and amps (flow) with little ohms (resistance)means a lot of watts worth of power. If you draw 200 amps out of your 100 Ah battery then you would exhaust the battery at twice its rated capacity and it will be flat in just half an hour!
You can see why a 200 Ah battery will run your microwave for twice as long as a 100 ah battery. When you parallel two similar batteries (done by connecting plus to plus and minus to minus) they each help each other handle the load so that you now have double the capacity. For example, a caravan might have two large 6 volt batteries connected in series to give 12 volts. Once connected, these banks of batteries (electrically speaking) look like and act like, one huge battery. You will see from this that there is a lot more to consider that just the power side of things. I would recommend that if at all possible you convert the house electrical system to 24v instead of 12v.
You will need and DC-DC converter to convert the 24v to 12v for the few things that need 12v (phone changers etc).
I always knew electricity was like water (only it bites), but never understood the meanings or methods.
I do undertake private consultancy contracts for people altering or building motorhomes and caravans. I will read every word on your site given the time but let me thank you for explaining electrics in terms that make sense .I have written down all the formulas and will re-read these over and over again until they are lodged in my head. I am an electrician and though I have heard similar analogies you win by a country mile in articulating things to facilitate understanding. It would be more costly, and could be dangerous (if for example you accidentally got 24v on the 12v vehicle system – now that would be costly!).
The alternator only produces the energy that is required – if it is required to produce more, it will put more load on the engine and the fuel economy will go down.


The issue with installing an unnecessarily large inverter is that they are very inefficient when running at low load.
This can be increased to 100% of the rating of the alternator IF the alternator is hot rated. Connect the Positive (+) input for your inverter to your positive earth block, and the negaive (-) to your negative earth block.
These batteries need to be replaced every few years to ensure the system performs correctly.
We are fairly experienced with electronics and suggest that this project should only be undertaken if you have done all the appropriate research beforehand (also see safety disclaimer on step 2). Because of the way we will connect these extra panels (in parallel – more on this in just a moment), we will be leaving the voltage the same, using the extra watts to boost the current (flow of electrons into the battery) and charge our battery more quickly. A large motorhome might have two large 12 volt batteries connected in series to provide 24 volts (it is just as valid to connect four 6 volt batteries in series to give the same 24 volts).
A fridge running from solar needs to be a low-voltage compressor type (preferably a Danfoss compressor type). You are planning a fairly large system and this is very difficult to do successfully at 12v.
It always works out more cost effective to get it right the first time and to have an independent person view plans and diagrams BEFORE they implemented. Now, I’ll go to read all other articles from your page, because I hope to get my motorhome ok at the end of 2013.
What is the implications of using a dual battery system and either a seperate 12v solar charger or a 12v to 24 v converter to charge the 24 v batteries in combination with a solar system? The system I am planning is comparable to a friend’s bus system, but he has a 24v alternator. It is very hard to keep negatives away from the ground – some appliances even connect the negative to the chassis of the device (a Waeco fridge that I had a few years back did this). They are designed to replace the current used in starting the vehicle (so say 50 amps for about 10 minutes) then slowly reduce the output to meet the requirements of the (normally small) load of the vehicles systems.
After experimenting with test UPS systems using cheap inverters and old car batteries I decided to scale it up. With batteries in parallel we are not changing the voltage at all – we could add 100 batteries in parallel and still have just 12 volts . It is just like having two water storage tanks side by side and combining them to flow from a single tap. It also shows the maths to work out how much current the aircon system would use if connected to the inverter.
I always like to arrive at a camp spot will full batteries, so I make use of the vehicle alternator most of the time (Our bus has controls to allow me to manually control the amount of alternator current used to charge the house batteries). A 2400w inverter supplying the same 950w load is likely to be around 70% efficient and thus draw 113amps to do so. Running an alternator that is not hot rated at near full load for an extended time will result in the magic smoke being released. Are you using the internal controller for the Magic Pier or are you bypassing to an external controller?? I will be buying a used motor home (have sort of set my heart on a “Coaster”) and was wondering if rather than looking for one already with solar panels which I would have no idea about, would it be better to get a bus without and then get exactly the right system added?
If you wired them as 24v (in pairs) the current would be a more reasonable 41amps – a Plasmatronics PL40 or PL60 would manage this current well.
The self resetting MCB will prevent a large current being drawn from the crank battery when the house battery is relatively discharged (first thing in the morning for example) AND prevent overloading a the alternator. Bikemad posted a good pic on the effects of wiring batteries in parallel compared to series.BTW, I noticed you have a bunch of lights on your bike.



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