batteries

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batteries

Postby zap » Wed Jun 20, 2018 2:33 pm

I am installing batteries into my bus for a solar system (1170 watts) and decided that 6 volt batteries would be best value per amp. Should I install four cells in series (24 volt @ 345 amp) or install two in series(12 volt @690 amp) and then another two in series (12 volt @ 690) paralleled to make 24 volts@ 690 amps.

It sounds more impressive to have more amps but i guess in the end it is all still going to make the same number of watt/hours. My thought is that as one bank of 24 they should charge more evenly.

any advise?
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Re: batteries

Postby Gordon-Loomberah » Wed Jun 20, 2018 2:45 pm

Whether you need 345 or 690AH really depends on what loads you have, their timing, how much charging you can get into them etc. One or 2 strings is ok, beyond that you may have some cell balance issues.

Another issue to consider is whether your 345AH battery can handle over 40A charging.
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Re: batteries

Postby zap » Wed Jun 20, 2018 3:00 pm

excellent point about charging I chose a 40 amp charger to handle the potential solar power but the victron inverter/charger may put more in than that. I will need to check that and from memory these can handle between 45 and 60 I will need to check that as well.

I do not need the higher amps as the system is currently running on 220amps @24 volt. but the person who did it set it up with the cranking batteries as the house batteries and I need to separate the two systems. It will mean not having any alternator charging but if the solar has a bad day or two I will need to top up.

Thank you
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Re: batteries

Postby Gordon-Loomberah » Wed Jun 20, 2018 5:54 pm

Just go with 345AH then. The cranking batteries are not designed for daily cycling type usage, so wont last as long as you might expect in that capacity- best to get them back to motor cranking duty only, ASAP.

You can get around any issue of too high a PV charging current for the battery by changing the arrangement of the panels, if that is feasible when parked. Face some to the east and others to the west to flatten out the midday peak. If they are all facing straight up, it may not even be an issue except on occasions in summer if you have cloud edge effect peaks in output with cool panels.
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Re: batteries

Postby zap » Wed Jun 20, 2018 6:02 pm

yep that is the plan regarding the cranking batteries.....stupid idea..............but regarding the east west I have that at home but on the bus just flat on the roof is the best option.

I was hoping to confirm that I would be correct in that I will get the same watt hours regardless of which configuration i used. and I have found some 435 amp cells for $700 each. should do the job.
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Re: batteries

Postby Gordon-Loomberah » Wed Jun 20, 2018 7:08 pm

The amount of storage in watt hours is found by multiplying the battery Ah by voltage.
345AH X 24V = 8280Wh = 8.28kWh
If you use the 435AH battery, then you'll have 10.44kWh of storage.

Of course you can't use all of it if you want the batteries to last a long time, and the actual amount of available energy is dependent on how fast you use it, due to the Peukert effect in Lead-acid batteries. The higher the discharge rate, the lower the effective capacity. At very high discharge rates the capacity might be only half of what it is at low rates. All reputable battery manufacturers list the AH rating for a range of discharge currents, usually expressed as a fraction of the battery capacity.
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Re: batteries

Postby Privatteer » Wed Jun 20, 2018 7:51 pm

zap wrote: @24 volt. It will mean not having any alternator charging


If the Bus and Solar system is the same voltage its still possible to keep alternator charging.
Basically you pick up a supply from the switched accessory fuse box and control a relay that only energized when bus is on.

Alternatively there are automatic battery isolators. They look at the voltage of the primary side and only energise when the volts are above a certain limit. Runs the vehicle battery down a little bit before disconnection but leaves plenty to start again.
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Re: batteries

Postby zap » Thu Jun 21, 2018 10:49 am

Thank you I can connect to the scary master relay. it is about the size of a big lunch box and the relay locks in with a really loud bang must have been intending to draw a lot of power when they built this thing. but as you say each startup I can connect the two systems for the drive time of cause batteries of this size will take a long time to charge but if the solar is not keeping up then at least it is putting something in.

I hate generators at any camp site. I am confident that I have enough power for sunny days and even though it is 40 foot long there is no more room for panels I will just have have to find ways to use less power. just need to find batteries to store the power. I really like the sound of the 435 amp they cost more but wow.
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Re: batteries

Postby Gordon-Loomberah » Thu Jun 21, 2018 10:54 am

You could always carry some extra panels in the bus to be set up at camp sites when extra power is required or in cloudy weather.
Of course, you could use Lithium batteries, which would allow greater depth of discharge, and are lighter weight. They are also more efficient, meaning you would have more energy available from your system under all conditions.
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Re: batteries

Postby zap » Thu Jun 21, 2018 11:15 am

Thank you Gordon I will look to see what is available. I have been looking at agms but because it is a coach I have a huge area under the bus for storage and could use the big 2 volt batteries but I don't like the idea of twelve of them not that weight is an issue. I have twelve at home and run my house on them quite ok. I could use any flooded batteries in the coach but Lithiums are also smaller. $$$
I will update this once i have found some batteries I could consider just getting some now and add more as I need them. If for example even with the best power management I still run out of power then get more. I am sure i have enough solar so storage is the only issue. and I prefer to have all panels on the roof active at all times rather than dragging them out at camp. That way they are working even while mobile and even while I am still lazy in bed the panels are already getting what little they can from the morning sun.
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