Dual Battery systems and Solar

Submitted: Saturday, Jul 30, 2005 at 11:14

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Nick (QLD)

I've been reading alot of posts recently in regards to dual battery systems interfaced with solar systems and thought it was worth mentioning the following point. As far as I know, In these type of scenarios it is important to remember that one source will cut out the other. This wont happen immediately but after ten minutes or so. For instance if you had a parrallel DBS, ie: VSR's, redarcs etc. running in conjunction with a solar system installed on the roof, the alternator will cut off its charge pretty quick. The reason for this is as follows. The regulators on the alternator are a single voltage output, unless 3 stage reg fitted, and the solar regs are 3 stage or triple output. Which ever unit is outputting the lowest voltage, the alternator in parrallel DBS, will step back because its under the impression something else is charging the battery better than it can. In many cases this is true or true enough. However, if your second battery is down considerably it would be preferable to have the alternator charging instead because it has a larger current out put and can do the job quicker.The only thing to remember is that a parralel DBS will only ever get a DC battery to about 85% but it will get it there fast. Ie: you are better off driving three hours and have the alternator put in say 10-15 amps per hour rather having the solar put in only say 4-6 amps, for an 80 watter, for each hour and thats only if in total direct sunlight, which it would almost never be. This issue can be managed by doing the following. The first step is to mount an inline switch in the positive line coming from the solar to the reg. Never from reg to battery as the solar reg cant handle it. Basically, If you believe or know that your battery(s) is down considerably and are moving to another spot you should switch off the solar and allow the alternator to do its thing. If the battery is basically full than your best off leaving the solar online as it will charge better from 85% - 90%. Any thoughts, corrections would be appreciated. Nick

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Reply By: Grungle - Saturday, Jul 30, 2005 at 16:23

Saturday, Jul 30, 2005 at 16:23

Hi Nick,

3 stage chargers are not triple output, they are only single voltage out but charge batteries in three stages (first stage boost - constant current, second stage absorbtion - constant voltage, third stage float). I wouldn't charge the starter battery with multiple sources at once because as you say the alternators output depends on a voltage sense line which means another source can trick it into thinking that battery is a higher voltage than it actually is. Any other sources should be switched in via a relay which is activated by the ignition. ie when ignition on, alternator charging - solar regulator not charging. Ignition off, alternator not charging - solar regulator charging. I believe the reg can handle having the switch between the reg and batt - that is how many switch the reg from one battery bank to another if they do not have the option of multiple outputs on their regulator.

Regards
David

AnswerID: 122884

Follow Up By: V8troopie - Sunday, Jul 31, 2005 at 00:46

Sunday, Jul 31, 2005 at 00:46

I do not believe that the first stage of solar chargers is current regulated, eg. 'constant current', its more likely flat out, letting all the current the panel can supply flow to the battery.
At least this is how I observe my three stage solar regulator on an in line Ampmeter, dealing with the current from the solar panels feeding it.

Second stage sends a 'pulsing' current to the battery. The on/ off timing of the pulses changes as the battery gets full.

Third stage is voltage regulated, letting only a small trickle charge flow.

Perhaps you were describing a mains operated, big bench top three stage charger and not the usual 3 stage solar regulator.

Klaus

FollowupID: 378085

Follow Up By: Grungle - Sunday, Jul 31, 2005 at 08:52

Sunday, Jul 31, 2005 at 08:52

The reference to the 3 stages of battery charging is the standard description given out by manufacturers. I didn't go further into it in the interest of keeping it simple. However the definition 'Boost' is a description by the manufacturers to signify 'Constant Current'.

240V 3 stage chargers and 3 stage solar regulators do exactly the same job. The only difference between the 2 is that the regulator can only put out what the panel produces. I have used our solar regulator as a 240V charger buy connecting a bench power supply to it set to 18V / 20A.

I totally agree that with 3 stage solar regulators, they do suck as much as the panel can produce but during the boost profile, it is the voltage that varies while the current remains generally constant if it can. The focus on the Boost stage is current and putting as much as it can into the battery. If the conditions are all over the place then the regulator will take what it can but at the end of the day the definition of Boost remains the same. This changes when it gets to absorbtion when it holds the voltage constant and the current varies. All 3 stages are controled by PWM.

A really good explanation of 3 stage battery charging (actually this site states 4 with the inclusion of Equalisation) can be found at this page.

Regards
David

FollowupID: 378094

Reply By: Mainey (WA) - Saturday, Jul 30, 2005 at 17:35

Saturday, Jul 30, 2005 at 17:35

Nick,
you say "as far as I (you) know" which does not demonstrate affirmation

I’ve only been using solar power – continuously, since 1997....

I believe I’ve learnt by practical experience during those eight years and can claim I know something about solar systems and recharging 12v battery systems, maybe not everything, but enough to suggest regrettably, I don't agree with your opinion.
Maybe I’ve not read as many books as some, and need to update my data :-)

AnswerID: 122898

Follow Up By: Nick (QLD) - Monday, Aug 01, 2005 at 13:07

Monday, Aug 01, 2005 at 13:07

The purpose of "as far as I know" is purely to suggest to you that I dont know it all and would encourage 'useful' feedback. However, in this case I have set up over a dozen of these systems and they all operate as I described. What don't you agree with Mainey?

FollowupID: 378214

Follow Up By: Mainey (WA) - Tuesday, Aug 02, 2005 at 13:06

Tuesday, Aug 02, 2005 at 13:06

(QUOTE)What don't you agree with Mainey?(end quote)

Nick,
This as you posted is what I don’t agree with, it simply does NOT happen.... :-(

(QUOTE) For instance if you had a parrallel DBS, ie: VSR's, redarcs etc. running in conjunction with a solar system installed on the roof, the alternator will cut off its charge pretty quick (end quote)

What actually happens is the Aux battery/s stop receiving Amps from the Solar panel, the reason is; the “smart” Solar regulator will see the Aux battery/s as fully charged, within a few seconds of starting the engine and the Aux battery/s being connected to the alternator via the battery isolator, because the Aux battery/s is receiving the full initial charge from the alternator, yes it may only ‘surface charge’ at this time but the “smart” Solar regulator does not know this, it just senses the Aux battery/s voltage as fully charged, so it cuts back the Amps from the Solar panel to Nil.
The Solar panel will still be sending all the produced Amps to the “smart” Solar regulator but the “smart” Solar reg will not send it to the Aux battery/s.

Scenario;
It must be remembered the Solar panel is suppling Amps to the aux battery system all the time the sun is shining, when the fridge is running and when it is off.

Time is 8.40am, conditions overcast, the fridge has reached its preset temp (+1 degree) and recently turned off, Aux battery are 12.6v and the Solar panel is delivering 0.6a to them, the vehicle engine is started and within only seconds the cranker battery is receiving 14.4v, the Rotronics isolator connects the Aux batteries to the Alternator and now both battery systems receive 14.4v from the Alternator, the Steca Solar regulator cuts back the Amps going into the Aux batteries at the rate of 0.1 amp at a time, till it receives Nil Amps, this only takes about five seconds and you can watch it happening on the LCD screen of the Solar regulator.
Information based on knowledge and practical experience :-)

FollowupID: 378398

Follow Up By: Mainey (WA) - Sunday, Aug 07, 2005 at 19:17

Sunday, Aug 07, 2005 at 19:17

More information...
is only useless if not of interest, and I would suggest you would not be reading this thread if you were not interested anyway.

3.15 am, yes dark, in the early hours when the partygoers are getting home.
Have driven 12 klms in the dark with the lights on , 'cause is easier to see the road, have let the vehicle idle while I check the relevant numbers.

Steca Solar regulator LCD screen shows 14.4v at Aux battery at idle!
No amps because it is dark as in no sun shining here, yet.... :-(
14.4v also at Starter battery.

That afternoon, 4.55 pm, overcast conditions, sun almost on horizon, engine off.
Steca Solar regulator LCD screen showing 13.9v at Aux battery because the sun is still shining :-)
Solar panel putting out 0.2 Amp
0.1 Amp going to Aux battery as both camp lights are presently being charged.
Start engine, fast idle after warm-up, for ~3 mins to check charge at batteries.
Steca regulator shows Aux battery now at 14.4v, and that was when the engine was idling.
14.2v when at fast idle speed.
Steca regulator still showing 0.2 Amps being produced at Solar panel
NIL Amps is now going to Aux battery due to it receiving full charge from vehicle alternator (14.4 amps)

FollowupID: 379122

Reply By: Nick (QLD) - Wednesday, Aug 03, 2005 at 09:58

Wednesday, Aug 03, 2005 at 09:58

What car have you got mainey? Something new like a 100 series I'd say. Reason being 14.4v is only available from alternator on certain new vehicles and some 'tweeked' older systems.

Most vehicles will never put out that higher voltage off the alternator where as any solar regulator will put out 14.4v on a boost charge and even more on equalisation. For this reason, the alternator will cut out because its putting out a lower voltage. Both regulators monitor voltage not current and disperse current depending on the voltage readings. (Using algorithms) This wont happen if the solar reg is in float mode,(14.1) unless your alternator puts out even lower than that. In this case it will operate as you have described.

The main point im making is that basically you want your alternator to do your bulk charging. If the batteries low you dont need very high voltage to charge it.(low internal resistance) So, why not use the 80 or so amp capability of your alternator instead of the comparibly tiny outpout of your solar.

Because, in most cases, the alternator will cut out, if the battery capacity is under say 85% I'm suggesting an inline switch to isolate the solar to allow your alternator to do it quickly. If your system is above 85% then let your solar do the job because a single stage alternator will rarely get a deep cycle above that capacity anyway.

Are you picking up what I'm putting down mainey?

AnswerID: 123521

Follow Up By: Mainey (WA) - Wednesday, Aug 03, 2005 at 23:04

Wednesday, Aug 03, 2005 at 23:04

Nick,
“ Are you picking up what I'm putting down Mainey “ Nope!

I’m on record as having a "tweaked" external regulator, it gives as I’ve posted 14.4Volts, because I have two 80A/H paralleled Deep Cycle batteries plus starter, to charge and the original regulator was not doing the job for me. It only cost ~$30.

My Solar panel is attached to a roof rack permanently, however it takes only minutes to remove and place in the sun with a length of security chain and the extension lead when I camp in the shade.

The reason my post (378398) was not posted the same day as I read your's was I had to wait till the following morning to do the actual test as I have posted above.

Every number is accurate and yes I did watch the LCD screen as the Amps reduced as I have posted.

I will stand by my post as being perfectly true and accurate in every single detail :-)

FollowupID: 378703