Parallel Question

[wildbill]

I already have a 65AH flooded deep cycle battery.....what are the problems....if any, with buying a new, say, 125AH Sealed AG deep cycle and adding it to the existing  battery????????

 

[Gypsy Freedom]

first, best practices suggest same same. so same chemistry same voltage and samme amperage.

that said, nothing is going to blow up. but you do have 2 dissimilarities going on there (actually three, i forgot to say same age/condition).

the difference in capacities is not a huge problem. technically when connected in parallel, the voltage stays the same and the capacity (amp hours) adds up. so yes, you would have what 190 amp hours then. the issue (just talking about mismatched amp hours) is that as you discharge one battery will "work harder" and you may wear out one or the other sooner.

the difference in age can be more of a problem depending on how long you have had the original and what condition it is in. an older battery can tend to drag down a new battery. worst case the new battery dies together when the old battery does and you lose the extra life you paid for from the new battery.

those to problems i frown on and certainly dont encourage. but i wouldnt slap your hand... lol

now the problem of mixing flooded lead acid with an AGM is the discrepancy in charge and float voltages. if you set your charging to what one battery needs, you WILL be hurting the other. either over charging one, or under charging the other. this will degrade one battery fairly quick. then you have the added problem of a degraded battery dragging down the other. again, nothing is going to blow up or catch fire by mixing these. and not like i am gona whack your hand with a ruler like sister bertha better than you. but if i came across something like that when helping i would realy encourage changing things up.

in the hypothetical case presented above. i would keep the 65 and add 2 more of the same, as long as the original is still in good condition

or i would ditch the 65, give it or trade it to someone and then get a 200 agm

or, depending on why you are upgrading, if just for more capacity, rather than the no off gassing of the agm. i would consider the best to ditch or pass on the 65 and get a pair of entry level FLA (flooded lead acid) 6v golf cart batteries. that will get you true deep cycle 200+ rated amp hours. with reasonable care and proper charging that would give you a solid battery bank

there are a lot of other variables, like how much capacity do you need?
how are you recharging?
do you have room for bigger batteries?
and more?

 

[MrNoodly]

I've read that we shouldn't even mix identical batteries of different ages, that the old ones will somehow drag down the new ones.

 

[wildbill]

Just for information, I am a newby, I bought a trailer that had this 65ah in it, and has a very small solar set up.....it's a Coleman 18 watt panel, the trailer has been rebuilt and shows no use at all, so I am doubting the battery has been used at all. I am stepping up the game with a 300 or 400 watt system.....probably a kit.....PMW.....I am pinching those pennies as much as possible.....trying to look ahead with the high wattage of panels while trying to keep it cheap cost wise. So, as long as no immediate crash and burn....so to speak and literal, maybe trying to just add a battery is worth it?

1972 Shasta Compact

 

[Trebor English]

You might start with figuring out how much electricity You are likel;y to need then design a system to provide that. It is not a minor upgrade from 18 watts to 400 watts. There is most likely nothing there that is useful with a 400 watt system.

A rough estimate, starting point, would be to consider a 400 amp hour battery bank as appropriate if your loads predict that you will want 400 watts of solar panel. Usually the battery bank size is determined then the solar array is determined to accommodate the needs of the battery considering your location.

You might reasonably keep the 18 watt 65 amp hour system and add an entire new system. That way you have some electricity if one of the systems fails.

 

[Gypsy Freedom]

with just doing a general up size with out build up for a specific load it is hard to say what is better. there are simple ways to add 300-400 watts with a good MPPT controller that are cheaper and much better that a cheap kit
a good MPPT system can get as much power from 300 watts of panels as a basic PWM sytem can from 400 watts of panels spending a little extra on a good charge controller can save you money in the end

if you could link the kit you are thinking of i might be able to help you get more bang for the same buck

do you have the model of the 65 amp hour battery? i am guessing it is likely not a real deep cycle.

depending on what sort of electrical use you anticipate spending money for a cheap battery up grade may be something you dont need or worse money spent that does not fulfill your needs. it might be better to use the battery you have and see how if fares after the added solar is added.

my recomendation is a similar scenario of a starter 300-400 watt system would be a pair of golf cart batteries. they can be had around $200 from local sources. and give you years of 200+ amp hours rated capacity.

 

[Gypsy Freedom]

A rough estimate, starting point, would be to consider a 400 amp hour battery bank as appropriate if your loads predict that you will want 400 watts of solar panel. 

this is NOT a good pairing for a general rule of thumb unless some specific need is in order. like having a large battery bank to go several days through a storm.

very simply if you need a 400 amp hour battery bank and deplete it to 50 on a regular basis the 400 watts of panels wont stand a chance of recharging the batteries each day. failure to reach full charge consistantly is the number 1 cause of early death of a battery bank.

also there is no "usual" way to determine ratio of panels to battery. if you have no info on what is needed then you just want to make sure you have the panel watts that are rnough in your local conditions to fully recharge the batteries regularly.

if you want to determine (instead of guess) what you need. then think of batteries as your power when the sun aint shinning. any power you need during those times need to come from the batteries. this could be just over night or it could be a few days while a storm blows through.

then to calculate the need for panel watts. first, if the calculated battery bank is going to be consistantly depleted each day then the solar gain needs to be enough to fully recharge the bank each day and this can easily take 125% of what was used. but if the bank only gets discharged deep in a occasional storm, then if it takes a couple days to recharge it aint so bad.

but secondly, aside from recharging the batteries from the over night, the panels also have to provide all the power to run everything through the day while still charging the batteries

if you have a large day time load with minimal night load like A/C during the day but just some led lights for a bit at night. you would need much larger panel watts with a small battery to get through the night. where as if you have large constant loads 24hrs like refrigeration and you also tend to watch a lot of tv at night with lights and running the fan on a heater. you are going to need a much large battery bank in relation to panel watts

figuring out what one needs is more than half the challenge in pick what panels/battery bank to get

 

[wildbill]

You might start with figuring out how much electricity You are likel;y to need then design a system to provide that.  It is not a minor upgrade from 18 watts to 400 watts.  There is most likely nothing there that is useful with a 400 watt system.  

A rough estimate, starting point, would be to consider a 400 amp hour battery bank as appropriate if your loads predict that you will want 400 watts of solar panel.  Usually the battery bank size is determined then the solar array is determined to accommodate the needs of the battery considering your location.  

You might reasonably keep the 18 watt 65 amp hour system and add an entire new system.  That way you have some electricity if one of the systems fails.


I was thinking that no matter what size battery bank I have, the 300 or 400 watt system would refill it quick. I have no idea what I will be using it for.....yet.....but I want a well rounded system such as solar, generator, and land power if available.....but probably need to be able to handle a fridge and laptop.....after hours.

 

[wildbill]

Fun fact.....I found out today that if I take my battery tender off of AC and plug it into the inverter …...it tells me where the battery percentage is.....it has a digital read-out. I know that I shouldn't leave it connected.....but for a quick read.

 

[Gypsy Freedom]

i run a sizeable fridge with separate freezer through an inverter with 435 watts solar flat mounted mppt controller (big help) and 100 amp hour battery. i also use my laptop considerably and charge from the same inverter my battery is useually floating by noon. today the sun didnt come out strong due to overcast till 2pm, still hit float shortly there after

i would stick with the existing battery till you find you need more

you fun fact intrigues me? what inverter is this and what battery tender? very curious. on the surface, it does not make sense

 

[wildbill]

i run a sizeable fridge with separate freezer through an inverter with 435 watts solar flat mounted mppt controller (big help) and 100 amp hour battery. i also use my laptop considerably and charge from the same inverter my battery is useually floating by noon. today the sun didnt come out strong due to overcast till 2pm, still hit float shortly there after

i would stick with the existing battery till you find you need more

you fun fact intrigues me? what inverter is this and what battery tender? very curious. on the surface, it does not make sense


Ok, it's a $59 dollar tender from Walmart.....I googled but didn't find it....didn't look very hard....lol.....and the inverter is an 800 watt modified sine wave …...el cheapo.....but if I plug the tender into the AC plug in on the inverter it shows me on the read-out at what percentage of charge the battery is.....I plug it in and push the analyze......and it comes back 75% or FULLY CHARGED....

 

[wildbill]

OK,,,,,,,the reason I am even saying to plug the tender into the inverter is so, when not having access to AC I can get a read-out

 

[geogentry]

@wildbill

A Tip or Two.

Try not to quote long messages. This uses up data for those on limited data plans.

But sometimes you need to quote. If you do then make sure you start typing AFTER the /quote inside of the [ ] or your answer may get cut off (like your last post did) and all of your answer won't show so we can read it.

Sent from my SM-J727V using Tapatalk

 

[Gypsy Freedom]

OK,,,,,,,the reason I am even saying to plug the tender into the inverter is so, when not having access to AC I can get a read-out

i see, it would do the same when plugged into regular AC or shore power right?

ya plugging it in to the inverter briefly to get the reading is just fine. the tender does not know or care where it gets the AC power from.

good on thinking outside the box

 

[Trebor English]

In post #8  wildbill said "I was thinking that no matter what size battery bank I have, the 300 or 400 watt system would refill it quick."  

That is a problem with lead acid batteries.  If you take out 50 amp hours you can't fully recharge it in an hour with a 50 amp charger.  Use lithium if you need good charging performance.  Lead acid batteries charge quickly from 50% discharged up to about 80% full then, while holding the absorption level, 14.4 volts or so, the current taken by the battery tapers slowly to zero.  

More solar panel will get the battery voltage up to the absorption voltage quicker.  The sulfur still must be moved from lead sulfate in the plates to sulfuric acid in the electrolyte.  That process is slow.  

A starter battery might run the starter motor for 2 seconds.  That's 0.00055 hours.  In that very short period of time the sulfur does not go very deeply into the plates.  Fifteen minutes of driving, 0.25 hours, is usually sufficient to recharge.

 

[Trebor English]

Your battery tender is not a battery monitor. Battery monitors are $150. They watch the amps going in, they watch the amps going out, they are programmed with the Peukert coefficient for your battery and they estimate the state of charge.

The battery tender looks at the battery voltage. If it does sense its output current it doesn't know how much is used by the fan and how much actually gets to the battery. Get a multimeter and measure the voltage at the battery. It is a poor indication of state of charge. The battery tender indication is worse because it sees the battery voltage through the same wires used to supply charging current.

If you really want to know the state of charge use a hydrometer to measure the density of the electrolyte. Less dense means the sulfur is in the plates as lead sulfate ions. More dense means the sulfur is in HSO4- ions in the sulfuric acid. This directly measures state of charge. A well maintained battery monitor can estimate the state of charge. A volt meter can give a guess about what's going on.

 

[wildbill]

i am sorry if i am eating up "data," but, when i hit reply to a comment it brings up the person's statement as well. Do i have to manually erase their message or what? Still trying to figure this out...….which, in my opinion, it should be easy, but it's not.

 

[wildbill]

@wildbill

A Tip or Two.

like this??? or down below this box???

Or down here???

 

[geogentry]

@wildbill

Hey, don't get me wrong. Was just trying to help you learn. [emoji16]

If you look at your post you will see the different effects of what you did. I think you have it though. [emoji106]

Yes it takes a bit to get the hang of things. No worries.

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