House batteries

Davianni · Member

House batteries

Whenarewethere · Guru

No quite sure what you are saying. Sounds like you have 2 batteries. If that is the case they are most likely connect in parallel. If you have a quality charger if will have a good algorithm & as the batteries get more charged it will reduce the amps & will go into float voltage eventually. If you have a "dumb" charger, replace it with a smart charger as you will shorten the life of the batteries.

Peter_n_Margaret · Guru

Davianni wrote:
..... if I am only supposed to run them down to 50%, .....

Urban myth....

Cheers,

Peter

bgt · Guru

Dumb question. Do batteries discharge in a linear fashion? ie with a constant load starting with a battery on say 12.7v, when I pull up , will the discharge rate slow as the battery looses volts. I have 1 210amph battery that quickly goes from 12.7 to 12.3 and then just sits there slowly going down to 12.2- 12.1 etc.

Peter_n_Margaret · Guru

Not exactly.... hmm

If the power draw is high, the voltage delivered by the battery will drop somewhat. The load is Watts, so to maintain the same Watts, the Amps will increase as the voltage drops.

If you maintain a heavy load, eventually the battery will not be able to maintain enough amps to sustain the load.

The power that the battery supplies comes from a chemical reaction inside the battery. If the chemical reaction can not keep up with the demand, then the battery can not maintain the load.

Think about cranking the car when it does not want to start. Eventually you can not turn the motor over. It is common belief that the battery is then flat, but in fact it probably is not, because if you wait a while, the chemical reaction catches up and you can crank the motor over again.

EDIT: I don't think I actually answered your question :( There is a chart somewhere that gives approximate SOC at various volts, but take great care with using it ços almost anything can give a false impression.

Cheers,

Peter

-- Edited by Peter_n_Margaret on Sunday 14th of June 2020 01:13:18 PM

bgt · Guru

Thanks Peter. We have always owned large motorhomes with large battery banks, solar and generators. Last motorhome fired up the invert or generator automatically. So never had to worry about managing batteries, it was done by some smart computer. Now we have a campervan with 1 x 210 battery and I get nervous and lost about power management. So far I'm impressed how our battery can cope with an electric only fridge, water pump and a few led lights. Mind you wife thinks I'm the power police! Battery drops to 12.2 and sits there for ages. I'm looking at a 200 solar panel just to top the battery up.

Peter_n_Margaret · Guru

More solar, more solar, more solar..... biggrin biggrin biggrin
Saves the worry and takes better care of the batteries.....

Cheers,

Peter

yobarr · Guru

bgt wrote:
Thanks Peter. We have always owned large motorhomes with large battery banks, solar and generators. Last motorhome fired up the invert or generator automatically. So never had to worry about managing batteries, it was done by some smart computer. Now we have a campervan with 1 x 210 battery and I get nervous and lost about power management. So far I'm impressed how our battery can cope with an electric only fridge, water pump and a few led lights. Mind you wife thinks I'm the power police! Battery drops to 12.2 and sits there for ages. I'm looking at a 200 solar panel just to top the battery up.

With a 210 battery you need minimum 300 watt Solar,I believe.Peter may elaborate? I have Solar that is over 3 times battery capacity.....1710 watts solar for 540ah Lithium.Cheers

Jaahn · Guru

Davianni wrote:
Gday all,
Finally off to our first trip even though its just down to Torquay! Quick question: I have 2 house batteries, now if I am only supposed to run them down to 50%, how will the charger know how to switch over From one to the other? Cheers for now

Hi Davianni smile

I do not think your actual question was answered well. The two batteries should be wired together "in parallel". That means they work as a pair sharing the load equally and sharing the charging equally. So just nothing for you to do there. aww

Jaahn

Davianni · Member

Thanks Jaahn, I think Ive grasped the idea.

Just come back from turning on the fridge and electrics ready for that HUGE trip to Torquay Tomorrow. I mean to note down the basics that newbies like me can understand. Cheers

Aus-Kiwi · Guru

Peter_n_Margaret wrote:
More solar, more solar, more solar.....
Saves the worry and takes better care of the batteries.....
Cheers,
Peter

So true .

Aus-Kiwi · Guru

A VSR fitted correctly can solve half your anxiety!! I have one fitted between motor battery . From Memory its a two way relay ? It isolates when under 12.5v so I can still start motor . Solar or alternator can charge both batteries!! It does its own switching . All I do is keep an eye on volt gauges . With 420 watt solar, over 300 amp hour weve only had to charge with generator 2 times in 4 years . 40 amp battery charger .

Peter_n_Margaret · Guru

yobarr wrote:
With a 210 battery you need minimum 300 watt Solar, I believe. Peter may elaborate?

I don't accept that relationship.

Charging capacity needs to comfortably exceed the power used, not the power stored. It is best practice to bring LA batteries to a proper full charge on a regular basis. They do not like being left partly charged for long periods.

Having excess storage capacity is a waste of money and excess weight, but it is not necessarily bad for the batteries if they are topped up regularly. Excess battery capacity also provides for occasional use of high current appliances like microwaves and the like that actually don't consume a lot of energy.

Having excess charge capacity (solar) is always good and having a back up charge option (like direct alternator or DC-DC charging) takes away the stress when the sun does not shine.

We have not carried a generator for 16 years of free camping for up to 8 months at a time. Expensive, noisy, polluting, dangerous fuel, heavy, anti social, and frighten away the local wild life. Not much going for them. furious Nor do we have 240V charger or a 240V power inlet of any type.

Cheers,

Peter

markf · Senior Member

Peter_n_Margaret wrote:
More solar, more solar, more solar.....
Saves the worry and takes better care of the batteries.....
Cheers,
Peter

Yep. Too much solar is like too much chocolate. There is no such thing... biggrin biggrin

bgt · Guru

Trying not to hijack the tread. Peter you mention the 50% is "urban myth". OK I have heard most theories. So my question to you is - if the 50% "myth" is in fact a "myth" then at what point are gel, agm and lithium batteries flat or lower than their safe/useful point? I've never taken our single 210amph battery below 11.9 volts but I haven't the means to tell what the actual amps are. I had a bus conversion with 1800+amph and never had an issues because the generator automatically start when they were low. But I forget what 'low' was.

Peter_n_Margaret · Guru

Lead acid battery manufacturers consider "flat" to be 10.5V, but some stuff will stop working before that and going below 10.5V probably is bad for the battery, so leaving some safety cushion is a good plan and somewhere around 11.5V is probably a sensible lowest point.
The myth of going under 50% has come about because the number of "cycles" for the life is clearly seen to decrease with regular discharges to low SOCs.
The first thing to understand is that "cycles" is not a sensible way to measure battery life at all.
Batteries tend to have a total life measured for their lifetime output in Watt Hours (or amp hours if that is how you think of the energy).

An example (made up numbers).
If we have a 100Ah (new) battery and use it down to 50% SOC each and every time and does that 500 "cycles" before being junk, then the battery delivered 500 x 50Ah = 2500Ah in its total life.
If we discharge the same (new) battery to 0% SOC each and every time and it did that for 250 "cycles" before being junk, then some would say it had half the life, but in fact it delivered 250 x 100Ah = 2500Ah in its total life, which is EXACTLY the same life as the first example.

In real life, deeper discharging does reduce the total life of a battery compared with shallower discharges, but the differences are relatively minor and not worth being too concerned about.
In fact there is a legitimate choice available. Buy 2 batteries at $300 each ($600) and replace them both every 8 years or buy one battery for $300 and replace it every 4 years (I made the numbers up, but you get the idea). There is some sense in replacing them more regularly - Less $s invested at any one time (but similar annual cost) and less weight to carry (but less battery back up time when the sun does not shine).

All of this information is typically contained in good battery manufacturer's data, but it is typically misinterpreted.
Cheers,
Peter

bgt · Guru

Thanks Peter. I have a deep mistrust of salesmen. We have owned 3 motorhomes. 35, 40 and 40 foot. 2 manufactured and 1 bus conversion. The 35ft was great for its day but predated inverters being common. (1996). 1 bus conversion with 1800+amph battery, solar and generator. All electric and never ran out of power. Then we owned a top end 40ft with more brains than space shuttle!!! Big everything, turned generators off and on and managed all the power. No solar. 2 slideouts etc etc etc. I'm getting to my point!! So after owning 3 large, smart motorhomes we decided we wanted the smallest and simplest motorhome we could get away with. An Horizon Fiat. Dc-dc, alternater charging, 210 amp but no solar. We wanted 2 nights or 44 hours without starting the engine either to drive or charge the battery. I didn't option up for solar. We are getting the 44 hours. But it's getting tight. So Horizon will install a 200 amp solar system. That we hope will get us a buffer. We have never even turned the tv on. Not even connected. No a/c, we're tough! So we aren't power crazy campers. So far the Horizon is a 9.5 out of 10. But I want the solar buffer. Hence the digging for info. I apologize to the OP for highjacking the thread.

Aus-Kiwi · Guru

I think you mean 200 watt ?

bgt · Guru

Thanks. Yup watts. Fat fingers or slow brain!!

Jaahn · Guru

Hi bgt smile

My comment would be put on twice as many watts and forget about the restricted power, might get lots of days instead of 44hrs. Just my thoughts wink

Jaahn

-- Edited by Jaahn on Wednesday 17th of June 2020 06:01:29 PM

bomurra · Veteran Member

Hi Davianni,

May I suggest that you check your batteries for the manufacturer's name and model number, it should be printed on the battery.

Once you have this information contact the local distributor or the manufacturer's website direct and obtain a copy of the Tech Data Sheet for your exact battery.

Once you have this, it will give you all of the information regarding battery life expectancy with differing depth of discharge rates etc. With some batteries constantly discharging them significantly below the 50% level will reduce their lifespan.

The TDS should also tell you the optimal charging voltages for your particular battery and the relationship between open cell voltage and state of charge of your battery. It is handy to remember that temperature has a role to play in battery performance as well, maybe not huge depending on where you are located, but should be born in mind.

I have attached a copy of the TDS for the Gel batteries Jayco use in their Silverline series, to better illustrate the above points.

You should also bear in mind that many Solar Controllers do not fully charge your batteries, so the state of charge of your batteries is usually not 100% if working from Solar exclusively, even if the controller may say so..

Jaahn · Guru

bomurra wrote:
Hi Davianni,
--------------
You should also bear in mind that many Solar Controllers do not fully charge your batteries, so the state of charge of your batteries is usually not 100% if working from Solar exclusively, even if the controller may say so..
_____________________________________________________________________________________________
Hi
My comment on bomurra statement above. There is no reason to say that solar chargers do not fully charge your batteries if you have a quality unit. But if you go to ebay or even some local outlets and buy a crap $20-50 unit then expect crap results. Probably includes most regulators fitted to portable panels also. You do not buy the cheapest rubbish for your tug servicing or phone so why not buy a good quality regulator. Use one with three stage charging and user adjustable settings to get the correct voltages for your battery.
However I might add that most people do not get their batteries fully charged regularly because they do not have enough solar panels IMHO. But there are lots of people who wander the country using solar panels only when stopped for a while and their batteries get fully charged and are working well.
jaahn

-- Edited by Jaahn on Friday 19th of June 2020 09:18:31 AM

Whenarewethere · Guru

Jaahn wrote:
You do not buy the cheapest rubbish for your tug servicing or phone so why not buy a good quality regulator.

One spends a fortune on a vehicle. Also complains if it is not serviced properly. On the other hand some fit it out with the cheapest crap possible.