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Post Info TOPIC: A poor man's battery charger


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A poor man's battery charger


From time-to-time most of us who rely upon solar panels and batteries for our energy will experience occasions when the sun doesn't shine for a few days and the batteries are depleting rapidly.

If, like me, you also carry a generator you have an option to put some additional charge into the batteries from the gen but as the 12V DC charger output on most gens is next to useless, and may damage batteries, you now need a battery charger and, to be useful, it's got to be a quality one putting out about 20A+ with multi stage charging and probably costing around $300?

But, hang on a mo', we already have a sophisticated battery charger but it's called a MPPT solar controller and if we disconnect the solar panels and apply a power supply to the solar input of the MPPT it will charge our batteries because it doesn't known the difference between a power supply and a solar panel.

I have a Victron 100V/30A MPPT controller and have recently purchased a quality 48V, 6.7A, 320W power supply from eBay and the system works very well:

Power supply

In order not to overload the power supply I restrict the MPPT to a 20A battery charge rate. Any power supply with an output voltage of about 20V and above but below the maximum input voltage of your MPPT controller will work.

Note: If your batteries are wired into your caravan/motorhome and charged by the on-board controller this system won't work for you.

Also note: this is all a little technical and requires you to understand a bit about electricity eg. Ohms Law, cable sizes, maybe making a 240V connection and such. However if it works for you it will save a few dollars, weigh and space.



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Deleted.

Sorry, I just realised that my system just receives the 12 v supply from the generator but is tricked up by the sparky to do what it is basically supposed to do and that is charge the batteries.

I dont know what he did but he did fit another component and a switch so that it can be turned on only when needed.

sorry if I confused anyone.



-- Edited by Clarky 1 on Saturday 4th of June 2022 12:02:28 PM

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Stu



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Hi Mike,

May be time to upgrade the solar system to LiFePO4 storage.

Don't have these power storage problems with Lithium and you can kiss goodbye the gennie.



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Cheers, Richard (Dick0)

"Home is where the Den is parked, Designer Orchid Special towed by Jeep Grand Cherokee Limited"

"4x250W solar panels, Epever 80A charger and 3x135Ah Voltax Prismatic LiFePO4 Batteries".



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Dick0 wrote:

May be time to upgrade the solar system to LiFePO4 storage.

Don't have these power storage problems with Lithium and you can kiss goodbye the gennie.


I don't think so.

Try camping in the forest in Victoria in winter.



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"I beseech you in the bowels of Christ think it possible you may be mistaken"

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Mike Harding wrote:
Dick0 wrote:

May be time to upgrade the solar system to LiFePO4 storage.

Don't have these power storage problems with Lithium and you can kiss goodbye the gennie.


I don't think so.

Try camping in the forest in Victoria in winter.


 Don't have battery storage problems so far this winter, rain hail or shine. And why would I want to camp in a shaded forest anyway...defeats the purpose of having solar. Find a little open area to let the light in because all you need is light and not only sunshine.



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Cheers, Richard (Dick0)

"Home is where the Den is parked, Designer Orchid Special towed by Jeep Grand Cherokee Limited"

"4x250W solar panels, Epever 80A charger and 3x135Ah Voltax Prismatic LiFePO4 Batteries".



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Dick0 wrote:
defeats the purpose of having solar. Find a little open area to let the light in because all you need is light and not only sunshine.

I understand this stuff pretty well Dick0 thank you, but I do not wish for my solar panels to dictate where I may camp.



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"I beseech you in the bowels of Christ think it possible you may be mistaken"

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I'm wondering what the firmware in the MPPT controller must be thinking. It is designed to expect a current source, but it is now connected to a constant voltage source. To determine the maximum power point, the controller would draw more current, see that the power is still increasing, and it would then draw even more current, generating even more power, and so on until it hits your maximum current limit setting. I suppose there is nothing wrong with that, but I wonder if the firmware can become "confused".

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dorian wrote:

I'm wondering what the firmware in the MPPT controller must be thinking. It is designed to expect a current source, but it is now connected to a constant voltage source.


Well observed Dorian and thanks for raising it, it's something I should have mentioned in my post. The MPPT controller behaves exactly as you suggest and may draw sufficient current to put the PSU into overload.

My Victron controller has a facility to limit battery charge current which I set to 20A for this 320W PSU, 20A equates to about 300W and keeps the PSU happy.

I have another cheap(ish) MPPT controller which does not offer a current limit but rather allows setting of absorb and float charge voltages which I initially set to minimum and gradually increase as the battery state of charge begins to govern the charging process.

As I mentioned originally; this is all a bit technical so if readers don't understand this discussion then it's probably better they buy a "proper" battery charger.



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"I beseech you in the bowels of Christ think it possible you may be mistaken"

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Mike Harding wrote:

..

But, hang on a mo', we already have a sophisticated battery charger ...

 


 What RV built in the last decade doesn't also have a 240V input battery charger?

Why would you use the low power 12V genny output when you can just plug the genny into the RVs 240V input and utilise that onboard 30+amp charger?



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>What RV built in the last decade doesn't also have a 240V input battery charger?

Indeed, and I covered that in my original post.

However all tents and many camping trailers do not have 240V charging facilities also it depends how one chooses to organise the electrics: I have left my caravan as original with its 100Ah battery, 120W solar panel and 240V charger and have organised my solar as a seperate portable system comprising panels, MPPT, inverter and batteries; a 240V cable is then used to connect the inverter to the van's 240V external connector. A major advantage of doing this is it gives me much greater flexibility in the placement of solar panels and as I usually camp in forests that is a real positive. I have put a time switch on the vans charger and it get two hours of 240V charging in the middle of the day which seems to be adequate without wasting power. There are advantages and disadvantages to doing it this way and it only really suits people who stay in one place for some time.



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"I beseech you in the bowels of Christ think it possible you may be mistaken"

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Mike Harding wrote:

>What RV built in the last decade doesn't also have a 240V input battery charger?

Indeed, and I covered that in my original post.

.


 Sorry, but I don't see anywhere in your posts the mention of the inbuilt 240V charger that most every van already has.

You mention now requiring a multistage 20+ amp charger for $300.

That is exactly what most every van and camper already has, inbuilt. We don't need to buy one.

I'm sorry I just don't see your point. Why would I want to run my genny through a solar controller, when the inbuilt 240V charger is more efficient.

If your original post mentioned your post was for tent users, then OK, but it didn't.



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Hylife wrote:
 Sorry, but I don't see anywhere in your posts the mention of the inbuilt 240V charger that most every van already has.

Then I can only suggest you reread it.

Similarly, if you consider my suggestion to be of no use then I can only suggest you don't use it.



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"I beseech you in the bowels of Christ think it possible you may be mistaken"

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In my case the multi charger / inverter only the inverter works the DC charger doesnt . Have found a few others much the same . It was easier and cheaper for me to buy a seperate battery charger . Makes a way better working system if your low on battery . A 10 - 20 min run on the geni or 240v power . Battery is charged to acceptable level ! Dont need to run geni for any length of time . If at all ?

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Upgrade to Lithium batteries and all your charging problems will disappear...rain, hail or shine.

And no need for a gennie anymore.



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Cheers, Richard (Dick0)

"Home is where the Den is parked, Designer Orchid Special towed by Jeep Grand Cherokee Limited"

"4x250W solar panels, Epever 80A charger and 3x135Ah Voltax Prismatic LiFePO4 Batteries".



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I hope your right . Just replaced AGMs with three 100AH Lithium !! Kept going into red on regulator


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Just for reference what make did you buy?



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Aus-Kiwi wrote:

I hope your right . Just replaced AGMs with three 100AH Lithium !! Kept going into red on regulator


 Post, when convenient, how the Lithium system is performing. Always good to know results of other Lithium systems.



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Cheers, Richard (Dick0)

"Home is where the Den is parked, Designer Orchid Special towed by Jeep Grand Cherokee Limited"

"4x250W solar panels, Epever 80A charger and 3x135Ah Voltax Prismatic LiFePO4 Batteries".



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Dick0 wrote:
Aus-Kiwi wrote:

I hope your right . Just replaced AGMs with three 100AH Lithium !! Kept going into red on regulator


 Post, when convenient, how the Lithium system is performing. Always good to know results of other Lithium systems.


 Agreed smile



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Up in Mackay I bought Fusion V-LFP-12-100.. They are working fine . 220l compressor fridge runs full time . I use inbuilt generator when boiling jug, cooking etc when camping . The 50 amp lithium charger keeps them charged when appropriate to use . Yet to sort out solar regulator . But it works fine !!

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Slightly off topic, if you have a flat car battery out in the bush, can you connect a portable solar panel to the car battery to charge it enough to start the car?  Has anyone done it?



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KevinJ wrote:

Slightly off topic, if you have a flat car battery out in the bush, can you connect a portable solar panel to the car battery to charge it enough to start the car?  Has anyone done it?


Yes, providing the panel is what is, nominally, described as a 12V panel ie. it has a no-load voltage around 20V. This would be OK with or without a regulator on the panel as a flat car battery will place sufficient load on the panel to keep its voltage down, however it would be wise to disconnect the positive terminal from the car in order that you are charging a stand-alone battery.



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Kevin j - you can hook up any voltage solar panel direct to the battery regardless of its nominal voltage because all that happens is the output voltage is clamped to the battery voltage and current flows gradually charging the battery HOWEVER you must monitor the battery voltage and disconnect the panel once the battery voltage gets to about 15 volts. If you can't do that then don't try it.

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Dick said "Upgrade to Lithium batteries and all your charging problems will disappear...rain, hail or shine.." Perhaps you could give us some info as to where we can buy these magic batteries you have, because otherwise your assertion is just plain nonsense

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Tony LEE wrote:

you must monitor the battery voltage and disconnect the panel once the battery voltage gets to about 15 volts. If you can't do that then don't try it.


 Obviously the only people who don't travel with a multimeter or better still a clamp meter are the ones who use a manual chainsaw!



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50L custom fuel rack 6x20W 100/20mppt 4x26Ah gel 28L super insulated fridge TPMS 3 ARB compressors heatsink fan cooled 4L tank aftercooler Air/water OCD cleaning 4 stage car acoustic insulation.



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My gel batteries have been brilliant. Can even supply 1040 amps for jump starting.



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Procrastination, mankind's greatest labour saving device!

50L custom fuel rack 6x20W 100/20mppt 4x26Ah gel 28L super insulated fridge TPMS 3 ARB compressors heatsink fan cooled 4L tank aftercooler Air/water OCD cleaning 4 stage car acoustic insulation.



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I carry both. biggrin



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Tony LEE wrote:

Dick said "Upgrade to Lithium batteries and all your charging problems will disappear...rain, hail or shine.." Perhaps you could give us some info as to where we can buy these magic batteries you have, because otherwise your assertion is just plain nonsense


Assume what you like and comment as you wish. I am stating my experience of my solar system, the details of which are stated at the bottom of every post.

I set up my solar system, so I do not need to rely upon direct sunlight only. My batteries fully charge to 90% in direct or indirect sunlight, overcast or inclement weather.

The difference is the daytime factor it takes to charge the batteries. There is nothing magic about the batteries. The magic is in the MPPT controller and the capacity of the panels.

Once you go Lithium with compatible charger and panels you never go back to flooded cells.

My system works for me with always an abundance of power storage. I no longer have a need for a gennie and run many 240V kitchen and other appliances day and night.

Taking into account that AGM batteries should not be depleted below 50%, then, I have approx. 800AH AGM equivalent usable capacity. 

That is my Lithium experience.

 



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Cheers, Richard (Dick0)

"Home is where the Den is parked, Designer Orchid Special towed by Jeep Grand Cherokee Limited"

"4x250W solar panels, Epever 80A charger and 3x135Ah Voltax Prismatic LiFePO4 Batteries".



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Dick0 wrote:
I am stating my experience of my solar system 

And I am sure you are truthful and correct.

However, the last I heard, you were near Longreach in Qld. - you will have a *very* different experience in Victoria and especially so in forest.

I have 800W of solar panel and Victron electronics: we recently had a few very overcast days and the best my kit could do was to collect about 300Wh on one day which is nowhere near covering the power budget of a fridge/freezer let alone the other stuff I use.

Come down to Victoria and live as I do for a year and you'll soon be buying a generator.



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Mike Harding wrote:
Dick0 wrote:
I am stating my experience of my solar system 

And I am sure you are truthful and correct.

However, the last I heard, you were near Longreach in Qld. - you will have a *very* different experience in Victoria and especially so in forest.

I have 800W of solar panel and Victron electronics: we recently had a few very overcast days and the best my kit could do was to collect about 300Wh on one day which is nowhere near covering the power budget of a fridge/freezer let alone the other stuff I use.

Come down to Victoria and live as I do for a year and you'll soon be buying a generator.


I am in Northern Victoria presently and still have no need, again, for a gennie. Even after the recent rains and general inclement weather. I have no issues with my system which fully charges daily. I have previously outlined my usage requirements which you have read no doubt, with great interest.

As I have stated before, my Lithium system works extremely well for me and I only express my experience. I do not make assumptions of anyone else's battery systems. Each his own.

I would like to hear from other Lithium system users and not those that assume they are experts in Lithium systems that they do not possess.

And yes, my Lithium system has been fully charging even in the recent inclement weather.

 



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Cheers, Richard (Dick0)

"Home is where the Den is parked, Designer Orchid Special towed by Jeep Grand Cherokee Limited"

"4x250W solar panels, Epever 80A charger and 3x135Ah Voltax Prismatic LiFePO4 Batteries".



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"I would like to hear from other Lithium system users and not those that assume they are experts in Lithium systems that they do not possess."

hi, I inherited a lithium system in my current rig , 6 years old, 4x70 ah batteries, each battery has a button that when pressed gives the voltage of each individual battery , these are available on Alibaba from China. Victron controller and monitor , Enerdrive 240 volt charger . Controller is blue tooth capable , monitor is not and very hard to read , need blue tooth version

In Coffs atm, unpowered site on day 17 , survived 3 rainy days Batteries dropped to 13.6. I run a Nova Cool 4.5 amh fridge , 12 v range hood , tv, lights , charge phone , laptop etc .
How ever the whole system died 9 pm the other nite after 1 rainy day ., batteries 11.1, turned off fridge which I had recently defrosted , next sunny day the individual batteries read 14.1 V , turned Fridge back on again at 4 pm, about 7 pm last nite back down to 13.2 .
Fridge not cycling off suspect faulty temp sensor, turned fridge off again , this morning reading 13.6 , and have wound back the fridge thermostat to 2 (was on 5) and now the Fridge is cycling again and not running continuously , a simple thing like adjusting the thermostat can save battery energy .
Currently at !0 .30 am, sunny morning Batteries reading 14.1 and are on absorbtion .Happy days .



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