Dual Battery + Inverter + Solar Wiring Setup (Seeking Feedback)

Lost me with the last sentence.
That statement is something quoted by self taught handymen that believe what they read on FB. Fuses are to protect the entire circuit not just the wiring including devices.

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Actually, and with the greatest of respect to QC, the function of a fuse is not so much as "protecting" anything. It is to limit the circuit current in the event of overload, including a short circuit on the wiring or within connected devices. In this way it prevents over-currents from heating the cable or connected devices to the point where they may initiate a fire.
Now that may appear to be pedantic but in electrical engineering there is a real difference between "protection" and "current limitation". Recognising that difference permits good circuit design.
To say "A fuse is to protect wiring not the equipment" is somewhat trite and misleading.
Sorry and no offence intended Bigfish.

There is one thing it protects Allan,that's the person who designed the circuit.
I'd hate to be the diy would be engineer that refers to FB forums and online calculators of unknown origin that causes a fatal fire or accident.

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QC, on this forum there is NOTHING that will protect you. lol

Alan this seems to be one of your usual arguments just for the sake of an argument. Limiting the current is protecting the cable from overload.

A fuse can be used to protect the wiring or both the wiring and a the device connected. If multiple device are connected to the cable then the fuse in the fuse box is usually rated to protect the cable. A good example of this is your house wiring, the circuit breaker in the fuse box protects the cable as you have no idea what is going to be plugged into the power points etc. Any devices connected to the cable should be either protected by their own internal fuse or be able to withstand any internal overload long enough to trip the breaker.

Allan haha just a thick skin ;))

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Your'e right Nick. I will don it right now to protect me from Leigh's waffle. lol

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Leigh,
Thank you for the instructional about fuses but we were actually discussing the semantics of the word "protection". And my post was to endorse QC's criticism of the use of the phrase "A fuse is to protect wiring not the equipment" as being misleading. But keep up the good work Leigh and do try to address the subject, not the man.

I used the term "to protect the wiring, not the equipment" Why??? Because that is what the fuse is for. All of my pieces of equipment...dc/dc, 240v charger, fridge, fans..all have their own appropriately sized fuse..So should I get rid of my 5.7/20 amp fuses and just rely on the 60 amp fuse at the battery for the "circuit"? I don't think so!!! My fuses are close to ther battery to prevent a dangerous event, like a fire , within the cable. If the equipment were to blow...stiff...easily replacable..BUT..the smaller fuses/circuit breakers should prevent damage.

The statement is incorrect no matter what lean you put on it. Why does a UHF have a 3 amp fuse when the wiring can easily cope with 15? It's because it is protecting the equipment and is 50% of the two components protecting against RP connection.

"The statement is incorrect no matter what lean you put on it. Why does a UHF have a 3 amp fuse when the wiring can easily cope with 15?"..

.. No way would you just put a 60/80 amp fuse on for 6AWG cable and expect it to protect the equipment. I,m sure I stated this in my original answer. Did I not say that 3 amp for equipment.i.e..radio and then a 80 amp for my 6AWG cable.

Lets agree to disagree...f,n 12 volt posts....

QC most of the components in a UHF radio can not be protected by a fuse. A fuse does not act fast enough. Or to put it another way, if anything happens in a UHF radio that will cause a fuse to blow, the equipment will have destroyed itself.

As for the bit, "Lost me with the last sentence.
That statement is something quoted by self taught handymen that believe what they read on FB. Fuses are to protect the entire circuit not just the wiring including devices." that statement is also used by professionals.

Back in the days of steam radio (valves,) if a fuse was blown by the radio, it was something in the radio burnt out first. When we were learning about transistors a favourite saying amongst the lecturers was "you can't protect a transistor with a fuse, the only thing you can protect a transistor is with another, faster transistor." Also, our experience was that when something fused in a radio, it was very rare for the supply fuse to blow as well. Generally, when there was something in the radio that caused the supply fuse to blow, there was also a burn up in the radio, or in other words the supply fuse did not protect the radio. All it did was to stop the radio presenting a good short circuit that would damage the supply cable if there was no fuse in the supply line.

Peter,
The diode, usually the first component on the cct board after the power lead connections in every UHF CB and many other 2 way radios I have repaired, either a large schotty diode or a large zenner is there to draw enough current to pop the line fuse before more serious damage is done internally so that fuse is important to protect against RP and over voltage connections. To me that is a fuse designed to protect equipment.

The broad statement "fuses are to protect wiring and not devices" is incorrect. Switches, relays,speed control units and heaps of other things that can be in a cct are also protected in the event of a short cct anywhere downstream in the cct and forgive me if I am wrong, they would clasify as devices.

Maybe a variation of the statement like "in this case the fuse is to protect the wiring", not just tack the broader incorrect statement on the end in an attempt to demonstrate superior knowledge when in fact it is doing the exact opposite.

When someone is pretending to know something they can only fool people that do not know but are easily identified by people that do know what they are pretending to know, and there a hell of a lot of them on social media.

That is the ideal way but not a law.
If you have more capacity than you need then compromises can be made.

OK back on track.
Dilan, Nick is quite correct about giving constructive comments on how you could have done it better would be far easier with a diagram but fact is you have already done it, so give it a run and see how it goes.

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Dilan, to add an image when posting, click on the box titled "Images and Files" then "Add Photos and Files". Select your file which must be in the correct format (jpeg or PDF will be acceptable) and add a "Title" (required) and click "Save".
The image will then upload and appear in your post.

You can never have to much capacity. :)
Dave.

Pleas check

I wouldn't be running more than a 300 watt inverter off a single AGM. Have you checked the max continious discharge rating? They don't go as well as lithiums.

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Hi Dilan,
You supplied diagram does not show where the fuses are positioned. It is important that each battery has a fuse positioned on or very close to the battery terminal and that no other cables are connected directly to the battery terminal.
It is unusual to have kept the inverter and its battery separated from the rest of the circuit. What are you using the inverter for?

Question: given that the 2000 watt inverter might draw 150 + amps ?? under full load is the 2 AWG cable on its limit ?
And would a re setable circuit breaker be better in this situation & best location for fuse/ circuit breaker.
Just asking
Cheers nick

Hi Dillon,

I am a little confused by your circuit diagram. It shows three batteries, Main Battery, AGM Under Bonnet and AGM in rear. Am I to assume that the “Main Battery” is your vehicle cranking battery? If so, why is it wired through the 40 Amp DC/DC Charger, and not directly off the Alternator?

Macca.

I'm wondering if you could connect the two batteries directly together for a larger amp hour charge given that someone said that the 2000 watt inverter might be too much for the 100ah AGM battery . But I guess that depends on what the inverter is going to be used for that Dillon has not stated as yet for its potential use .

Macca is there a problem with connecting the DC charger from the battery and not the alternator ?

Nick,

Let me state that I am not an Auto. Elec. or a 12 volt expert, so perhaps I am reading the diagram incorrectly, but it appears to show the connection from the engine (I assume Alternator) going to the DC/DC Charger, and then from the DC/DC Charger going to the cranking battery. If this is actually how it is wired, I think you will have a problem with fully charging your cranking battery, as the DC/DC can only deliver 40 amps per hour.

If the DC/DC Charger is actually wired from the Cranking Battery, you probably need to show the connection differently in your diagram. Also it would be wise to to have a VSR between the cranking battery and the charger to prevent your cranking battery from being discharged too low.

Thanks Macca I didn't notice that before , bit weird or it might be working on the theory of charging the auxiliary battery first before the cranking battery ??

But more importantly for my point of view was your VSR comment . do you connect the battery through a VSR or straight to the positive cranking terminal .
I was told that connecting straight to the positive cranking terminal in conjunction with my victron 30 amp dc charger TR that the auxiliary system would not flatten my cranking battery . Even know I have an old redarc vsr installed I bypassed it thinking that it would be one less thing to go wrong .

You should not need a VSR in association with a dc-dc charger as the charger will turn off when the input falls below 12.7 volts which is taken as the cessation of the alternator supply (stopped motor). If the charger is a type that incorporates an 'ignition' input signal voltage then it will turn off with 'ignition off'.

There is a case with a car and caravan with a dc-dc charger in the van to use an ignition-controlled solenoid in the feed to the car tow plug. This ensures that the plug is not left 'alive' when the car is parked and prone to vandal interference. But that is another story.

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Leigh, for Godsake stop editing your post. My email inbox is overflowing.

If you aren't up to it Allan. It would also help if the editor didn't do strange things ie display it differenlty in the post to what it does in the editor.

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That's dreadful Leigh. What "editor" is that?

The default editor for the Forum!

OK, after having had the time to have a good look at your diagram I very much hope you haven't actually installed that mess.

Do a bit more research and start again.
There is no prize for using more Anderson plugs than they can produce in a year.

It is impractical to have 2 batteries so far apart in parallel in a high discharge application.

As mentioned earlier use a single lithium battery in the rear and a single charging system, it will be cheaper and far easier to install.

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Actually QC, there are no batteries in direct parallel. They are all separated by dc-dc chargers with the inverter being supplied by one auxiliary battery and all general consumers supplied from the other.
Also, the rear 20A charger may not engage to charge until it sees a sufficiently high enough (typically 12.9v) voltage at its input. Certainly, it is not a circuit that I would choose.
Why is it that people want to design 'different' schemes rather than adopt proven ones? You should see the variety of circuits that the Yanks come up with on the MB Sprinter forum. And with battery capacities of up to 1000Ah.

That Allan is one of the bits that doesn't make sense which you mentioned earlier. 2kw inverter on a single AGM? 3 AGMs in close parallel maybe but still pushing them.
For a new install why even consider AGMs these days, they are cheap now compared to good quality AGMs.

Dilan, have a good look at it and think how it could be made simpler, 1 battery, 1 charging system with from alternator and solar. Then your fusing requirements will be much simpler. KISS is best.

QC it might be that Dillon already had the equipment and it might not be a new install just an upgrade .
Or it could be that some people are still a little nervous about lithium

Anything is possible Nick but unlikley that would be an existing system, and if that's an upgrade I'd love to see from what.
Hopfully it is just in the planning stage and he has had the sense to ask for some constructive criticism.
It's a shame to see people spending money on un necessary components on a system that won't work.

Thanks for your feedback, not many bother.
Just a point of interest, if you don't already have the hardware your battery in the back could be lithium seeing it is on its own charging system and it could also have solar input into its dcdc charger. The cost difference for say a 70ah lifepo4 and 100 ah AGM would be minimal and weight and performance advantages well worth considering.
One last thing I would suggest is a means to feed power from the rear battery to the front circuit in the event the front battery fails or just runs flat until you have the means to charge or replace it, just to keep the fridge going.
Good luck and safe travels.

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Dilan, it still is not making much sense. Your system would work better and cost less if you put both batteries in parallel (or a single 200Ah lithium battery) in the rear of the vehicle with a single 40A dc-dc charger at the battery and supply both the inverter and all other accessories from that battery bank.
Apart from a simpler and more effective system you avoid putting an AGM battery in the hot engine bay.

It makes no sense to have one dc-dc charger obtaining its supply through another charger. I have never seen this done and cannot imagine why one would do so.

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Dilan, another point about your inverter draw from a 100Ah AGM battery.
Firstly, it is recommended to not regularly discharge AGM batteries below 50% of their rated capacity, so your usable capacity is only 50Ah. So you might expect to run the inverter for about 30 minutes. But not so, because….
Secondly, these capacity (Ah) ratings only apply when the load is low, typically like 5 or 10 amps over a period of 10 hours. The nature of AGM batteries is that the faster you discharge (more amps) then the efficiency falls and you get less Ah than you would expect. It's called Peukert's law.

The reality is that your 100Ah AGM battery will only be able to support your inverter for about 5 to 10 minutes when running at 500-1000W before the battery is exhausted. Furthermore, the lifetime of the battery will be severely reduced when operated at these high discharge rates.
You will likely be very disappointed if you proceed with your current plan.

On the other hand, lithium batteries can be discharged down to 20% or even 10% of their capacity so you can get as much as 90Ah from a rated 100Ah lithium battery. Furthermore, lithium can deliver at high current without loss of efficiency so you can obtain this 90Ah in full. This then would support your inverter for maybe 50-60 minutes.

So a single 100Ah lithium battery in the rear could effectively provide your needs. Your pair of AGM's will fail miserably. Think about it.

Hi Dillon,

Thanks for your comments regarding feedback. Your diagram still shows that you are charging the cranking battery via the DC/DC charger and not directly from the alternator, is this still correct?

Secondly, further to Allan’s comment regarding LiFePo4 vs AGM, in the back of my wagon, I replaced 120 AmpHr AGM with a 175 AmpHr LiFePo4 after I had installed a 2,000 Watt inverter. The Inverter is used to run a Coffee Pod machine that pulls 1,300 Watts. The inverter would trip out when the Coffee Pod machine was started. The replacement 175 AmpHr LiFePo4 battery has a continuous discharge rating of 250 amps, and runs the Coffee Pod machine with ease along with the 60 Ltr. Engel Fridge that is also connected directly to the battery (not via the inverter). The battery is a PowerPaul Australia 175 Amp Cub battery.

Macca.

Macca,
Maybe those cables are supplying the DCDC unit as the wire from the engine symbol is labled ACC so is likley representing the IGN feed to the DCDC.

Dilon .
I'm with Alan I don't see the sense in this design . Note : not that I'm qualified to make any auto electrical/ Engineering advice . The updated diagram is in my mind only cosmetic and not really addressing the design factors , aswell
BIGFISH brought up the that the diagram appears to show that the vehicles charging goes straight to the 1st DC charger and not the main battery ?? , If so , why ?

If it was me , I would be at least designing the system with correct size cable from the battery to the 2000 watt inverter , not relying on a fuse to limit the inverter to half it's capacity . I don't think anyone thinks that the 100 amp hour AGM is ever going to cut it ....

your most likely going to want to upgrade the battery in some way in the future &
I can't see any benefit in splitting the batteries system especially if you're not going to be using the inverter to any extent .

Nick,
There are times to run 2 seperate systems, such as medical equipment running of a devoted battery but charging through two DCDC units in series is normally only employed to limit overall load on the alternator when a second temporary system such as in a camper trailer is added now and then, in this case two 20 amp units would be more logical.
Ultimately there is only one logical configuration that can have minor variations to suit personal needs and everyone here can see this but Dilan seems intent on giving his design a go.

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Dilan, the DC charger should not be fed an ACC signal, it should be an IGN signal.
The purpose of the ACC signal it to activate the charger only when the engine is running and hence the alternator is active. The ACC (Accessory) signal becomes +12v when the key is set to provide accessory's with power without the engine running and this is NOT when the charger should be turned on.

Hi Allan, yes it’s ignition signal. My bad for choosing incorrect terminology ??

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Hi Dilan,
OK then. There is just one change I would now recommend to your scheme.
Do away with the 20A rear charger and simply connect the rear battery directly in parallel with the under-bonnet AGM battery using 4AWG cable as a minimum.
This will still limit the max load on the alternator at 40A, charge both batteries simultaneously and allow solar charging to the rear battery.
The most important benefit is that it will much better support the inverter by drawing from both paralleled batteries. The distance between the two AGM batteries is not ideal but is better than what you propose.
It would be even better to move the front AGM to the rear, close to the rear battery, which would get it out of the engine bay heat and save on cable cost whilst better contributing to the inverter demand.. But perhaps you cannot allocate space for it in the rear?

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Dilan, I would add that I operated a very similar circuit in my Troopy for many years. I had two 100AH AGM's in parallel in the rear of the vehicle charged by dc-dc charging. I did not however have the burden of an inverter.
Initially, I had only one AGM in the engine bay whose life was shortened by heat. Moving it to the rear and adding a second AGM solved the problem completely. The batteries were about 5 years old and still providing essentially full capacity when I sold the vehicle.

Hi Allan : would it be possible to have the two charges charging the under bonnet AGM together 'although different amperage ' ,
I have seen a install where they had two charges of the same amperage and also had a toggle switch that they could turn them off and turn them off individually as well ?

I also like your suggestion previous , I think Dilon would be wise to have a look at this at least . Unless he had a reason to split it , having not said what the purpose of the inverter would be used for .

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Hi Nick, if two power sources are joined in parallel to supply a load then the individual current contribution would depend on the characteristics of the individual sources and would likely differ.
In the case of these power supplies being dc-dc chargers whose control algorithms incorporate both voltage and current regulation then I could not predict their behaviour. One may dominate or they may play nicely together. Especially so if they are not of identical specifications. Why do you propose this as an option?
I also cannot imagine why someone would elect to have switches to turn their chargers on and off. I would expect a properly designed system to run satisfactorily in the background without intervention or supervision.

Thanks Allan :
Hypothetically thinking ...
If Dilon was to take you up on your suggestions above regarding doing away with the 20a rear charger and connect the two batteries together , so if it was possible to run the two DC charges together he could just use the 40 amp normally and then if needed at any stage to bump that charge to 60A he could switch the second charge on .
For instance if he had run the batteries down overnight and was only doing a short drive the next day ...

I can't remember why in the tutorial I watched the reason for two charges and a toggle switch..
I'll have another a look at that tutorial

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Ah, I see Nick. Paralleling the output of two chargers to sum their capacity.
Well, I have never tried it and I dunno, it may work, sort of. However in thinking about it I can see problem possibilities. You certainly can put two (or more) similar basic dc power supplies in parallel provided that they are of the same voltage and they will share the contribution based on their individual impedances. But dc-dc chargers are not simple dc power supplies…. they have control algorithms and functions that could raise problems. For instance, they typically pause their output regularly and briefly for two purposes…. a) to observe the battery terminal voltage without the effect of a charging current, and b) to observe the input voltage without current flow (and hence cable IR drop) to determine if the alternator voltage elevation is still present rather than just the voltage from the cranking battery.
If two chargers are in parallel there is no guarantee that this action will occur simultaneously and so the pausing charger will be misled by the effects of the other still operating charger and probably cause erroneous actions of the chargers behaviours. Such a parallel system may seem to work but may be acting the fool a bit without realisation. It may present as dinky but is not good engineering practice in my book.

Some time ago I did actually have reason to concoct a similar but practical scheme. The Troopy started out with a basic AGM auxiliary battery in the engine bay with a 20A dc-dc charger. Then I added a second AGM in the cabin charged by its own identical 20A charger and moved the original battery and charger from the engine bay also to the cabin. So each battery had its own dedicated 20A identical charger but were never charged in parallel. When the engine was off and no charging taking place, a relay joined the two batteries in parallel to share the house loads. I only did it this way because I had two 20A chargers on hand and recognised the peril of putting them in parallel.
It worked fine until I wanted to add solar whereupon I replaced the two 20A chargers with a single 40A charger that incorporated a solar input facility and put the batteries in permanent parallel.