It probably comes down to the temp setting on the EvaKool and location/mounting of your panels. I just spent 5 days on AGM/Solar, two day mixed alternator/AGM then another 2 days AGM/solar with my Evakool TMX75, 140ah AGM and 160 watt folding panel. All in mixed overcast mid 30s temps. Ran fridge just above freezing (for insulin storage) plus recharged a number of devices and lights. Battery never got lower than 12.1volts.

sarg wrote:

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I have a 70ltr 12v Evakool Fridge/freezer running 24/7 through a 130amp deep cycle battery. During this hot summer months in NW NSW the 200w solar panel charging the battery was only just keeping up the charge. Cause the hotter the temp. The less efficient the panel worked. So I went and put another 220w panel on. 

The question is ...Is 420w of solar too much for a 130amp battery.......through a 30amp regulator?? 

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 Hi sarg 

If you have a good regulator that has 3 stage control and goes into a suitable lower float voltage in the third stage of control there is no problem and it will keep the batteries in good condition.

If you have a cheap controller with a single fixed voltage then it will over charge them in the long run and you should get a better one.

Jaahn 

-- Edited by Jaahn on Monday 16th of April 2018 07:40:26 AM

Thank you all for your feedback. Cheers.

sarg wrote:

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The question is ...Is 420w of solar too much for a 130amp battery.......through a 30amp regulator?? 

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 420 W of solar equates to around 25 A of current if you are using a PWM controller. With the panel flat on the roof you will be pushing to get 80% of that - or 20 A on a good day. You should be OK with that on both counts (battery acceptance and controller rating.) If you are using an MPPT controller you will get a little more current available to charge the battery but not enough to stress a 30 A controller or your battery.

Peter_n_Margaret wrote:

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And on days of lousy sun, you will still get a reasonable charge.
Provided you have a decent regulator, you can't have too much solar.

Cheers,
Peter

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With lead acid batteries you can actually have too much solar unless you have a solar controller that is set up to measure the current flow before it drops into float mode rather than a timer based progression from absorption to float mode. The problem arises if the solar input current is higher than the battery acceptance rate. When this occurs the terminal voltage rises faster than it would if the charge current was lower than the acceptance rate. This increase voltage triggers the controller to switch from bulk charge to absorption charge mode. If the controller uses a time based absorption cycle to float cycle change the controller will drop into float mode before the battery is actually fully charged or even up to 90% charged if the solar output to battery acceptance ratio is very high.

So, you really can have too much solar on some occasions if you are charging lead acid batteries. Believe it or not, it can actually happen with lithium batteries as well, but we are now talking about very large solar arrays, generally greater than 2500w and a battery capacity of 600Ah or less. The problem there is cell voltage run away and a clever BMS switching the charging off until the cell voltage drops. The result is a constant over cell voltage charge cut (HVC) yet as soon as the charging is cut the cell voltage drops below what would be considered fully charged. The fix for this problem would work for lead acid batteries as well, some of the solar is switched to water heating duties and the problem goes away. We generally use a voltage on and lower voltage off or state of charge to drive this solar output shifting, for lead acid say 14v on and 13.6v off.

 

T1 Terry  

Terry, that is no different from plugging a 240V charger into a 2400W supply. The charger needs to control the charge rate. If it can't, chuck it in the bin and get a decent one.

Cheers,
Peter

Peter_n_Margaret wrote:

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Terry, that is no different from plugging a 240V charger into a 2400W supply. The charger needs to control the charge rate. If it can't, chuck it in the bin and get a decent one.

Cheers,
Peter

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Exactly, if you can't reduce the charge current from 50 amps down to 20 amps if you are only charging a 100Ah or smaller battery , the charger is simply not suitable for the job. Trying to charge too fast will result in the charger reducing the charge rate to maintain voltage and then dropping into the next lower voltage charging regime resulting in an even lower charge rate being applied by the control system to hold the voltage down to this lower rate.

Try charging a battery that is accepting the full current at 14.4v and drop the charging voltage to 13.8v, is the charging current still the same as it was at 14.4v?

 

T1 Terry

 

T1 Terry

swamp wrote:

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HI
Ritar up to 25% fast charge of Ah rating 120ah 30amps charge rate .
Personally 25 amp per batt is a little more on the safe side . Apparently its the heat build up that's the issue .
In saying that I run close to 400 watts with mppt so that equals max 28-29 amps . That's only if I flatten the batts greater than 25% discharged approx. I see that output
Many times I only use the 400W on 1x agm 120ah . The other is in the shed .. Charged up by smoko easily.

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 Not having a shot at you Swamp or anyone reading this, just trying to dispel any misunderstanding when it comes to lead acid battery charging.

At a 30 amp charge rate it would be well into absorption mode by smoko and possibly even dropped into float mode. It would be no where near fully charged unforunately because only lithium batteries can be charged at that rate until 98% SOC, lead acid is more likely to be at around 80% SOC at best at that charge rate over that time period. If the battery was genuinely fully charged before the 25% discharge the battery would still be at 75% SOC or 12.55v under a 6amp load and hold 12.8v under the same 6 amp load by smoko if it really was charged up. An easy test to prove me right or wrong, turn off the solar and put a headlight across the battery terminals, does it still read 12.8v after 5 mins while still under load?

 

T1 Terry

The best way to determine if the battery is really ready to switch to float mode is to push it back into boost mode voltage but at a low current and watch the charge rate. If it quickly drops back from say 5 amps to 1 or 2 amps, it really is ready to switch to float mode, but if the 5 amps remains constant and the voltage does not climb back up to the end of boost mode voltage, then the charger has prematurely switched to float mode.
The max charging amps is a heat generated issue as mentioned by another poster, not the optimum charging current to get a good balance between fast charging and getting the battery as close to fully charged before the charger drops into float mode.

To get an idea of what the manufacturer considers fully charged we need to look at their charging regime they use for cycle testing to determine battery life. Some manufacturers such as Fullriver say that fast charging should be limited to 0.25CA or 25 amps per 100Ah advertised capacity yet Fusion batteries say 0.15CA or 15 amps per 100Ah advertised capacity until 2.45v per cell is reached. Because most batteries these days don't have access to measure single cell voltages the 14.7v (6 x 2.45v) is used. The absorption cycle is then started holding the same voltage until the charge current drops to 0.012CA or 1.2 amps per 100Ah advertised capacity or a max of 8 hrs.
It is quite likely that some of the 6 cells will be higher than the 2.45v and some being lower than 2.45v and cell damage from under charging/over charging will result but there isn't a lot that can be done about that so often the absorption voltage is dropped to a slightly lower figure and the current at the end of absorption stage is also dropped slightly lower.
The charging cycle now moves to float charge at 2.275v per cell or 13.65v per 100Ah advertised capacity and is continued for a further 8 hrs, Fusion extend that to 24hrs.

So, it's clear to see it is impossible to fully charge a lead acid battery using solar and impossible to fully charge a lead acid battery while it is still being used so it will always be a compromise between cycle life and getting as much charge into the battery we can in the time we have available. Very few chargers are set up to suit the regime used by the manufacturer, but holding the solar charge rate to 14.4v will certainly get a lot more into the battery than if the charge rate drops to 13.8v early. This would of course require careful battery temp monitoring and lowing the charging voltage if the temp got too high, but good quality chargers have that ability.

As you can see, charging lead acid batteries is a real science and not something the average rv user will ever achieve, but getting the batteries to the 90% plus mark should be achievable using a quality charge controller.

T1 Terry

Peter_n_Margaret wrote:

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Terry, you seem to be saying that (for instance) a "dumb" 85A alternator should not be used to charge a 120Ah lead acid battery?
I have one that has been doing that to the same Fullriver AGM battery now for almost 8 1/2 years, and it seems to be working quite well thank you.

Cheers,
Peter

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You need to read further into the posts Peter, an 85 amp alternator may put a good current flow into a very deeply discharged battery for a short period, but adding up the current flow and multiplying it by the time that current flow is maintained you will see there was not a lot of capacity returned to the house battery. 85 amps for 20 mins is only 28Ah and a fraction of the capacity required to bring a deeply discharged 400Ah deep cycle battery pack back to a 100% SOC. The same alternator feeding a 40 amp DC to DC charger will put 40Ah into the same battery in 1 hr along with any solar charging available at the same time if a PWM controller is used but unfortunately not so if an MPPT controller is used. A 5 hr drive could replace 50% of the 400Ah battery capacity if it was deeply discharged before the drive started yet 40 amps into a 400Ah battery is only a 0.10CA charge rate so the battery could be charged at that rate till it was a lot closer to the 90% SOC than a faster charge rate could.

 

Really only of interest for those who plan to stick with lead acid batteries I guess, it is not applicable to lithium batteries but some form of charge current limiting would be required to stop the "dumb" 85 amp alternator going up in smoke due to over heating, they are not designed to run at a 100% output rate on a continuous basis. Special alternators are available that can actually put out a continuous high current but they are really designed for off shore cruising boats and not automotive use.

 

T1 Terry 

Peter_n_Margaret wrote:

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I think the vast majority of people are sticking with lead acid for their crank batteries Terry, even those who choose to use Li for the house. There are distinct advantages to have them all the same, as I do.

Cheers,
Peter

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I agree that cranking batteries mounted under the bonnet are the realm of flooded cell starting batteries, but these are not suitable for house batteries, never were and never will be. Many are now opting to do away with the cranking batteries and any batteries under the bonnet at all and going to the lithium house battery to do the lot. Makes far more sense to use one set of batteries that can do both jobs and make that bank big enough to do a lot more than separate starter batteries and house batteries can do and reduce weight at the same time.

There is no such thing as redundancy when it comes to lead acid batteries because you can't swap out a single cell and still carry on until a replacement cell is available and with modern battery management systems flat batteries are a thing of the past. A lithium battery that has had 100% of its advertised capacity used still has plenty left to crank over a large diesel engine so the idea of being able to link in the house battery to start battery to get over a flat battery situation is a thing of the past as well.

That 85 amp alternator belting in that 28 Ah before the lead acid battery voltage rises enough to cut the charging voltage back is also a thing of the past, alternator temp sensing allows a very fast recovery from a 100% discharge to bring the battery pack up enough to turn the engine off after 30 mins and let the solar do its thing and then maybe another 30 mins around 4pm if the solar hasn't been real good that day puts 80Ah plus back into the battery and that will run the fridge for 24hrs. You just can't do that with lead acid batteries no matter what you try.

 

T1 Terry

Yes Terry, there is only one way and it is your way.

Pity about the thousands of others doing it successfully some other way. They are all just batteries.

 

Cheers,

Peter

I could equally claim that our (and your) motorhome lifestyle is completely different and far superior to that of a caravanner, and that hundreds of other motorhomers agree with me (and they do).
Does that mean that all those caravanners are wrong?
If I was selling motorhomes, I would be tempted to say "YES, THEY ARE WRONG", but I don't sell motorhomes.

And, by the way, our chosen batteries do everything that we need them to do (and we do more than most, including many Li users) at a price that we can afford. When we need them to do something else, then we might consider a change to something else. They are only batteries. They don't make power, they just store it until it is wanted.

Cheers,

Peter

 

-- Edited by Peter_n_Margaret on Friday 25th of May 2018 05:06:17 PM

Your missing the point Terry we all hnow that lithium is superior ,but at a huge cost,people do not have to resort to that huge cost to achieve all the battery power they personally need for there circumstances,you will never understand this Terry because it does not suit your agenda,I mean no offence just expressing one mans view...