# Battery myth or fact ?



## spatz1 (May 19, 2011)

Theres a wealth of contradictive information surrounding batteries if you delve into a little research and being the one thing we all rely on, making a bit of sense to it all and sepperating myth from fact seemed a good start when it came to designing for my personal needs and manner of use of my motorhome....

Obviously i was blessed with the usual 4a charger / 20 a stable power supply most have and the "standard" 110ah battery but a 60w 12v solar panel came as standard too.... and its perfectly fine for the odd night off ecu ...

Six months ago, i paralleled a second 110 ah battery, but having read much i decided to purchase one of dubious nature in that it had been stood ages and only showed 9v but tested good and was rediculously cheap....Topped it up with distilled, a quick 4 stage recovery charge and it s proved to be "as new" in function thus dispelling the first myth that i came across in that a low voltage kills a battery..... 

content with my purchase these last months, i couldnt resist another that came up 3 weeks ago in a similar state and more rediculously cheap, the only possible draw back it was not of a similar capacity at 85ah.... No problem, research demonstrated the telecomunications industry have been mixing capacities for years as well as new and old so i promptly paralleled it in and decided to re wire the lot using 65a cable and laying that on to roof level having projected a large solar system to be fitted at some point in the near future.... (370w 44v via iva mppt regulator to maximise low level light performance)... I ve monitered the batteries as they charge and have seen no problems in this configuration and they seem to be functioning in the manner expected and dispelling another myth in that you cant mix differing capacities...

So i now have 305 Ah of battery capacity and obviously the van 4a charger isnt going to keep them healthy and there seems to be good reason to believe it would struggle to properly maintain 2 x 110 ah batteries judging by the premature battery failure evident on the forum... I fitted a 20a 3 stage charger the other week (also capable of compensating for hab use) and wired it via a spare 240v breaker and in use its proved to charge very quickly ( 7 hours is the longest its taken but the batteries were very low)...

I now have the choice of using the 20a rapid charger or the van charger, or both together obviously working in tandem with the solar during the day....thus dispelling a third myth that you cant add a boost charger while on hook up. ( think about it , those with solar have been charging with 2 systems for years when hooked up, so it was reasonable to expect my third method wasnt going to cause problems)

In practice with all three methods of charging simultaniously , when the batteries reach 14.8v charging drops to a float of 13.7v and 11 watts and stays like that indefinatly....( the 14.8v is enough to ensure the batteries are well maintained )

Granted its early days yet,(all monitered by a digital powermeter) but i ve had no problems thus far and am just waiting for the solar upgrade and have hopefully eliminated as much voltage drop as possible by laying the 65a cableing on....( it was cheaper to buy sets of jump leads as a source of cable than buy 30a cable  )

My costs will be £600 the majority of that 2x 185w quality solar panels and the quality mppt (which have a good resale value when done with) plus my labour :lol: :lol: 

My aim was to be self sufficient for 4 days in winter months and be able to recharge fully overnight on hook up if need be and not go down the route of skimping on power usage (especially led lighting that i found gives too white a light and is not "cosy")....

Daft as it sounds , off hook up i ve been using a neat 45w tube heater via the inverter and mounted it behind the curtains to keep the gap between them and the windscreen warm and condensation free and to prevent cold downdraft   

Hopefully, my research will have proved beneficial and my power solution will prove to be relliable despite pushing the boundaries a bit and i ll keep you informed if things dont perform as expected....


----------



## pete4x4 (Dec 20, 2006)

You may have a balancing issue as one of your batteries is lower capacity and will reach full charge earlier than the other 2 thus could potentially gas due to the higher than needed voltage being applied to it.
Keep an eye on the levels.


----------



## peedee (May 10, 2005)

spatz1 said:


> Six months ago, i paralleled a second 110 ah battery, but having read much i decided to purchase one of dubious nature in that it had been stood ages and only showed 9v but tested good and was rediculously cheap....Topped it up with distilled, a quick 4 stage recovery charge and it s proved to be "as new" in function thus dispelling the first myth that i came across in that a low voltage kills a battery.....


How did you test it to show it was good? Sure you can bring most back up but the damage already done would not be immediately apparent. You can only judge how good a buy it was by the life you get out of it.



spatz1 said:


> content with my purchase these last months, i couldnt resist another that came up 3 weeks ago in a similar state and more rediculously cheap, the only possible draw back it was not of a similar capacity at 85ah.... No problem, research demonstrated the telecomunications industry have been mixing capacities for years as well as new and old so i promptly paralleled it.


Well I worked in the telecoms industry for over 30 years and never came across batteries of different capacities connected in parallel. Even the battery banks I helped maintain were checked weekly and if any were suspect they were removed and replaced with one of identical capacity.

There was a very good basic program on the Caravan Channel recently about batteries which can be seen >here|<

peedee


----------



## spatz1 (May 19, 2011)

Both batteries were tested using the correct battery tester that displayed digital voltage and 3 lights , red fail, yellow weak pass and green pass....

There is a wealth of information on the net regarding the telecom industries practices and findings when it comes to battery banks...

As regards gassing, it can be clearly seen on my power meter that to a certain extent the "rogue" 85 ah battery is self regulating as it clearly reduces its watts intake within the system...and obviously never goes above 14.8v then drops to float as the others do. but i will keep a close eye on it...

Here s another thought.... if i conect a 400w inverter to the "cab" battery and feed the 20a rapid charger from it when driving.... i take it i will trick the alternator into feeding it and have a further means of rapid charge at 20a whilst on the move rather than just the paltry 3.5a the alternator soon drops to via the split charge relay ?? :wink: :wink:

In brief... would it not be better to purchase a rapid battery charger and inverter to supply it from the cab battery that serve a multitude of purposes, than buy the expensive gizzmo some use that tricks the alternator into providing 50a to the hab and does nothing else....

just questioning the boundaries we ve set ourselves :lol: :lol:


----------



## pieterv (Feb 3, 2009)

spatz1 said:


> Both batteries were tested using the correct battery tester that displayed digital voltage and 3 lights , red fail, yellow weak pass and green pass....


You can get most batteries back up to a normal voltage, that doesn't mean that their capacity hasn't been affected by having been left deeply discharged earlier.


----------



## spatz1 (May 19, 2011)

pieterv...

very true,
but i fully charged them and used the van 4 nights taking 160Ah out of them and the voltage was still a respectable 12.3 when stood some time after the usage(solar taken into account)... wasnt sure how else other than useage to test them....

Back to concerns of gassing , having been in the van last night i put it on fast charge at 4.15pm with the 60w solar having put in 5 ah today and raised the voltage to 13.6... by 6.30 the charger cut to trickle being fully charged and had delivered some 36ah and raised the voltage to 14.8....
whilst it was charging i did a visual inspection on the gassing of each battery and they all looked very much the same ...
finally i conected my 4 stage dogs danglies car charger to the batteries and it ran for 20 minutes at its very low amperage before cutting off and registering full just to confirm my suspicion that my20a charger was a quality item and charged to its standards...


----------



## spatz1 (May 19, 2011)

This is part of my research and demonstrates best why we have come to " believe" you cannot combine differing capacity batteries....

http://screencast.com/t/66JvY0sb6ag

The article its taken from explains in depth all about consequence of a cell failure in parallel and series systems etc and is just one of many i ve based my system on.....

in short the myth you cant use differing capacities in parallel would seem to have grown around the fact you cant with SERIES...


----------



## EdsMH (Apr 25, 2007)

Spatz

Very interesting and good of you to share what you are doing. Keep us informed on how the project performs over time.

I am just going through similar thoughts on investigating solar having got quite a robust level of battery support.

Off to search the forum for guidance and deals now panel prices are dropping so significantly. 

£1.17per watt best so far  

Ed


----------



## spatz1 (May 19, 2011)

i m now doing a battery capacity test using the inverter to supply a 100w bulb and a 240v clock .... the clock will stop when the inverter cuts off at 10.6v ..

i can then use simple maths to calculate how many ah capacity i have for "safe" use ... i can also re test at a later date to see if there is any deterioration in the batteries and also check to see if the figure is what i should expect from 305Ah capacity of batteries...

Or i can caculate accuratley simply by measuring how many amp hous to re charge to full...


----------



## HeatherChloe (Oct 18, 2009)

spatz1 said:


> My aim was to be self sufficient for 4 days in winter months and be able to recharge fully overnight on hook up if need be and not go down the route of skimping on power usage (especially led lighting that i found gives too white a light and is not "cosy")....


I agree - I can't charge with electricity at home, and I don't want to have to go to sites all the time.

My solution - a generator which runs off the calor gas.

Generally, this has worked really well - half and hour to an hour of charging and I have a full battery.

Combined with a bridge between two batteries, it is actually two full, large batteries.

Unless generator weirdly doesn't work, this solution means I am self sufficient constantly, not just for 4 days.

Worth a look, if you're keen on that kind of thing.

Especially in winter when you need the battery to run the hot air pump part of your central heating.


----------



## spatz1 (May 19, 2011)

spatz1 said:


> i m now doing a battery capacity test using the inverter to supply a 100w bulb and a 240v clock .... the clock will stop when the inverter cuts off at 10.6v ..
> 
> i can then use simple maths to calculate how many ah capacity i have for "safe" use ... i can also re test at a later date to see if there is any deterioration in the batteries and also check to see if the figure is what i should expect from 305Ah capacity of batteries...
> 
> Or i can caculate accuratley simply by measuring how many amp hous to re charge to full...


I ended up using 2x 60w bulbs and a 15% loss through the inverter gave a measured 11.66 amps that ran for 10.5 hours before low voltage cut off..... ( i was only able to charge the batteries to a full 14.8v)
11.66v x 10.5 hours gives a "useable" 122 ah....from 305 ah of batteries...and is ok for 4 days with no hookup and not accounting for solar input...

I conceed my batteries although testing ok may not the best but i d assume when manufactures quote 110ah for a battery it has been conditioned to give the best figure possible and probably had an equalising charge to 15.5 v minimum and i doubt you ll ever get that quoted performance from a battery in use ... thus i m not too disapointed with my results and they surfice my needs !!

job done :lol: :lol:


----------

