- Thread starter winchman
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RonA
specialist in repairing sealed for life equipment
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Both should just charge up to their relevant capacities.
I have a 125 W solar cell for my caravan when I’m stuck on a site without mains.
I’ve fitted a 1300 W inverter (mainly to allow the missus to use her hair dryer on a morning) problem I find is the battery fully charged is about 12.8 V but the inverter has an auto cut off at 11.8V so can’t pull a heavy load for long. Two batteries would help me too but stuck for somewhere to fit a second battery.
RonA
I have a 125 W solar cell for my caravan when I’m stuck on a site without mains.
I’ve fitted a 1300 W inverter (mainly to allow the missus to use her hair dryer on a morning) problem I find is the battery fully charged is about 12.8 V but the inverter has an auto cut off at 11.8V so can’t pull a heavy load for long. Two batteries would help me too but stuck for somewhere to fit a second battery.
RonA
CompoSimmonite
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Batteries should be same capacity if you want full charge in both otherwise they will just level out at the lower Ah.
RonA
specialist in repairing sealed for life equipment
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That’s what I thought as well
RonA
you can mix capacites of battery but not chemistry
personally i hate parralell battery systems i'm a belivere in say one big 200AH 12v battery rather than 2 x 100ah batterys or worse 4x50 ah. batterys seem to work much better in series means more volts and less current so things are more efficent ( but its not allways practical )
personally i hate parralell battery systems i'm a belivere in say one big 200AH 12v battery rather than 2 x 100ah batterys or worse 4x50 ah. batterys seem to work much better in series means more volts and less current so things are more efficent ( but its not allways practical )
winchman
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Never seen a 200AH? I can buy two 110AH quite cheaply
https://www.ebay.co.uk/itm/12V-110A...144312&hash=item3a8cb03bcb:g:T0MAAOSwt7pXMuqW
https://www.ebay.co.uk/itm/12V-110A...144312&hash=item3a8cb03bcb:g:T0MAAOSwt7pXMuqW
I've fitted plenty of 230Ah and bigger capacity batteries on boats, as far as mixing and matching them our advise is always NOT TO, ideally you want the same capacity, same chemistry, same make, same model, basically the same everything if you want them to last.
There is an old saying that is very true... Most batteries don't die a natural death, most batteries are murdered !
I hope you've got a monster battery as the amps you're gonna be trying to pull out of a single 12 volt battery with that kind of load are stupidly high, as an example we had one owner wanting to run his kettle off his battery bank, he was pulling around 240amps from his bank of 1380Ah... our advise was save your batteries and just boil a kettle on the gas hob instead.
RonA
specialist in repairing sealed for life equipment
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You’re absolutely right, the missus only gets about 10mins on low heat setting on her hairdryer but she seems to be happy with the arrgt. Solar cell manages to replenish the battery across the day ready for next morning. Switching to LED lights in the van has made a huge difference. Everything else runs on bottled gas, result the missus is happy ergo no ear bashying so I’m happy.
RonA
normspanners
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exactly .. as stated on another post re boats I designed a air powered water pump for central heating because a battery pump would kill batteries in a short order.
Totally agree Danny same as twin parallel battery set ups in vehicles they never REALLY work unless totally isolated from each other and charged separately and then combined when needed to power something ie starter then disconnected again.
I've been parraleling van batteries since I was a little kid and never had any problems at all
On a car/van/truck etc. The batteries get a good full charge every time you drive
A good full equalising charge is what majes the difference and jerps thrm healthy
On a car/van/truck etc. The batteries get a good full charge every time you drive
A good full equalising charge is what majes the difference and jerps thrm healthy
^ Can you post a diagram as to how you are wiring them up then, because there are many ways I've seen it done and most result in some batteries doing more work than others and/or some batteries getting overcharged whilst others sulphate from a lack of charge.
normspanners
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spot on wookie, that is why boat people spend thousands getting it right and it is not easy at all.
normspanners
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It will work as a bodge or temporary 'Fix' but one battery is allways lagging, And even series battery connections, which in theory is the best way, has its problems, batteries that are in theory exactly the same, are NEVER really exactly the same. the connectors, the wiring all has an influence, people that say it works, and I am sorry if it upsets people, do not know the intricacies of the problem If it is that easy WHY would engineers and technicians have spent millions trying to perfect it ? and failing.
you just wire them up in parallel, join the positive and negative terminals together... decent thick wire of course, same size or larger than wire to starter
charging from an alternator there's no way one should ever be under charged - alternators put out over 14v, which is more than enough to fully eq charge a battery
if the batteries are in parallel they'll both be at the same voltage so they'll both charge evenly (to the same voltage aka % of charge)
(as long as both batteries are decent to start with)
unless they're being run down too low there's no reason for any of them to die.... run them too low and you'll kill them all pretty quickly but one will die first (other won't be fr behind)
I re-wired a boat for a mate, two massive starter batteries, he had a disconnect switch between them because he thought he couldn't leave them connected together...
when I re-wired I permanently wired them in parallel and added an extra (sacrificial) battery which was connected to the pack via a big relay power on/off by the alternator output
that battery powered his float switch pump... so was the only thing with any load on it... that battery was knackered pretty quick.... but it doesn't matter, it's only powering the pump and it's good enough for that, it gets charged every time he runs the engine
the two big batteries are still perfect, that was a bit over 6 years ago - he's never had batteries last so long
(edit, to be fair, I say they're perfect... they haven't been tested, just start the engine every time like they're new)
charging from an alternator there's no way one should ever be under charged - alternators put out over 14v, which is more than enough to fully eq charge a battery
if the batteries are in parallel they'll both be at the same voltage so they'll both charge evenly (to the same voltage aka % of charge)
(as long as both batteries are decent to start with)
unless they're being run down too low there's no reason for any of them to die.... run them too low and you'll kill them all pretty quickly but one will die first (other won't be fr behind)
I re-wired a boat for a mate, two massive starter batteries, he had a disconnect switch between them because he thought he couldn't leave them connected together...
when I re-wired I permanently wired them in parallel and added an extra (sacrificial) battery which was connected to the pack via a big relay power on/off by the alternator output
that battery powered his float switch pump... so was the only thing with any load on it... that battery was knackered pretty quick.... but it doesn't matter, it's only powering the pump and it's good enough for that, it gets charged every time he runs the engine
the two big batteries are still perfect, that was a bit over 6 years ago - he's never had batteries last so long
(edit, to be fair, I say they're perfect... they haven't been tested, just start the engine every time like they're new)
normspanners
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The alternator is shut down by the higher battery voltage, the lagging battery is then not charged enough and will only attain a certain capacity and never go higher it is well known fact this happens. 'Sometimes' you can be lucky and the batteries are matched and receive and equal charge it is a well documented but it very rarely does. the lagging battery then 'pulls down' the good battery when connected together long term.
Why are these technologies a problem for auxiliary battery charging?
leisure batteries will usually suffer when connected parallel with a std battery.
Do whatever you feel like with your expensive batteries but please dont accept that it is as easy as a lot of people maintain, I have done it over the years when younger believing the same ideas and not listening to more experienced autosparks and it allways proved it is not a reliable system, it might work if you are 'lucky' but usually doesnt and any serious autosparks will confirm this fact.
That is a generalisation not all do, there is a vast difference between alternator voltages and smart charge alternators especially should never be connected to two batteries long term https://www.12voltplanet.co.uk/auxiliary-battery-charging-in-vehicles-with-smart-alternators.html
Why are these technologies a problem for auxiliary battery charging?
Whilst these new technologies are great news for the environment they cause problems when it comes to charging a second battery in an after-market application for the following reasons:
An auxiliary battery will not be charging for significant parts of a journey
During the periods when the smart alternator output is below the charging voltage threshold there will be no charging taking place. These periods can be significant when combined over the full length of a journey meaning that any connected auxiliary battery will not receive as much charge as it would if connected to a system with a traditional alternator.
leisure batteries will usually suffer when connected parallel with a std battery.
Do whatever you feel like with your expensive batteries but please dont accept that it is as easy as a lot of people maintain, I have done it over the years when younger believing the same ideas and not listening to more experienced autosparks and it allways proved it is not a reliable system, it might work if you are 'lucky' but usually doesnt and any serious autosparks will confirm this fact.
What you need is a split charge diode. These are common and cheap, and they enable two (or more) batteries to be charged from the same source, regardless of those batteries' differing capacity.
Sterling make one at around £40 which uses diodes with reduced voltage drop.
Sterling make one at around £40 which uses diodes with reduced voltage drop.
Kayos
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After wasting hours and hours reading up on split charge, joining batteries and the huge amount of different opinions I decided I’m fitting a second alternator and battery, with a method of temporarily joining to the main battery if needed
