connecting a smart charger to panel input on solar charge controller?

Submitted: Sunday, Apr 28, 2013 at 10:06
ThreadID: 101911 Views:3276 Replies:4 FollowUps:8
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Hi
I am camping with my brother who has a 80w solar panel charging van battery through a cmp solar regulator. He also has a ctec 15amp 8 stage smart charger. The regulator keeps a reading of the total cumulative charge to the battery and cumulative load on the battery. If he connects the charger straight to the battery, it will bypass the regulator and thus the cumulative charge readings will be incorrect. Is it possible to connect the smart charger using the solar input to the regulator. This would mean the readings for the cumulative charge would still be correct. My thoughts are that connecting the charger in normal mode may cause problems due to voltage readings, but wonder if connecting in power supply mode would be appropriate.

I would be interested to hear if someone is doing this, or if it is safe/appropriate to do so.

Thanks Kc
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Reply By: Member - John and Val - Sunday, Apr 28, 2013 at 14:36

Sunday, Apr 28, 2013 at 14:36
kc - Sorry, won't work. The controller won't accept the charger and the panels simultaneously. The charger won't like the higher panel voltage being applied to its output and may be damaged by it. With the panels disconnected, the controller is designed to manage the panel voltage and will not manage the lower charger voltage. So No - don't do it!

One other point - don't take too much notice of the cumulative charge readings. Batteries aren't 100% efficient so a simple calculation of input - output doesn't give a net charge figure. In fact the controllers assume a certain efficiency and calculate that in - BUT - effiiciency varies quite a bit with temperature, age of battery and the size of charge/discharge currents, so the net figure is pretty rough. A good indicator, but a poor measurement.

Cheers

John
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Follow Up By: Member - John and Val - Sunday, Apr 28, 2013 at 15:38

Sunday, Apr 28, 2013 at 15:38
Just to clarify - my wording above is horrible! - the solar controller is expecting to see solar panels capable of an output voltage up to 20+ volts. The charger won't deliver more than about 14.5 - 15V, so the solar controller won't know what to do with it.

The smart charger won't know what it's about either if it isn't connected directly to the battery. Overall, not a good idea!

Cheers

John
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Follow Up By: Member - graeme W (WA) - Sunday, Apr 28, 2013 at 22:35

Sunday, Apr 28, 2013 at 22:35
Hi John and Val. This may be slightly different and if you read the post i put up today on solar test you will see my setup. When we are camped in shade with not enough sun for the panels to work and when at exmouth every year insread of running my fridges on 240 volts i just leave my xantrax 40 amp smart charger hooked up to an anderson plug connectected to my back battery (used mainly to connect the van battery for charging when travelling) and either run the gennie or 240 if availible to keep the batteries charged to run the fridges. My solar regulator simply cuts out when it sees the high voltage from the xantrax thinking every thing is charged. Been doing this for 7 years now.
Cheers Graeme
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Follow Up By: Member - John and Val - Monday, Apr 29, 2013 at 08:30

Monday, Apr 29, 2013 at 08:30
Hi Graeme,

Yes - good way to go. Our own system relies entirely on 12V, maintained using a 240V charger if mains power is available when sunlight isn't. Keeping the solar charging and 240V charging independent from each other as you (and I) do is fine. The only interaction is, as you say, that the solar controller sees the charging voltage from the mains charger and concludes that the battery is now full. No problem.

However, the original poster was considering hooking his 240V charger into the SOLAR INPUT of his controller so that the controller could monitor net in/out current flow. Nice idea, but with insurmountable problems! Far better to simply connect the OUTPUTS of both charging sources directly to the battery and let them get on with the job!

Cheers

John
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Reply By: kcandco - Sunday, Apr 28, 2013 at 19:45

Sunday, Apr 28, 2013 at 19:45
Thanks John

Much appreciated. what a pity.

cheers

Kc
AnswerID: 509960

Reply By: kevmac....(WA) - Sunday, Apr 28, 2013 at 21:04

Sunday, Apr 28, 2013 at 21:04
Dont use Solar panels myself, but learnt the hard way when connecting a smart charger across battery when also running a high current drain fridge. It confused the hell out of the charger so much, that after a few trips i tossed the charger. I now only leave minimal & necessary items across the 12 volt system.
AnswerID: 509963

Follow Up By: oldtrack123 - Sunday, Apr 28, 2013 at 22:04

Sunday, Apr 28, 2013 at 22:04
Hi
Yes heavy loads can confuse any multi stage charger .
& can lead to possible overcharging of the battery!!!


PeterQ
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Follow Up By: Racey - Monday, Apr 29, 2013 at 09:10

Monday, Apr 29, 2013 at 09:10
Most smart chargers have "power supply" mode which delivers 13.8 volts. It's ideal for charging with a load connected; in fact my projecta charger recommends it to avoid over charging.
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Reply By: Jason – Perth - Sunday, Apr 28, 2013 at 23:07

Sunday, Apr 28, 2013 at 23:07
Hi KC,
John has correctly said that it won't work in the configuration you described, although I say the intent you seek is achievable. That is to say, you can have a mains powered supply connected to your brother's system with no negligible effects.
Connecting a smart charger across a battery in this way is pretty useless as you have found. There are power supplies available that emulate a solar panel very effectively (with MPPT regulators only) and when connected to the solar panel input, will recharge the battery at the maximum rate possible (determined by the max current of the supply).

Regards
Jason
AnswerID: 509971

Follow Up By: kcandco - Monday, Apr 29, 2013 at 20:25

Monday, Apr 29, 2013 at 20:25
Hi Jason
Can you please give more info re the power supply. What are MPPT regulators and what voltage should the power supply put out? 18v? Is something like this suitable? I hope link works.

30A power supply

Thanks Kc
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Follow Up By: Jason – Perth - Saturday, May 04, 2013 at 21:29

Saturday, May 04, 2013 at 21:29
Hi KC,
MPPT stands for Maximum Power Point Tracking. A Solar panel will change it's output of volts and current depending on angle of the sun, cloud cover and shadows covering the panel. An MPPT solar regulator will track the changes in the maximum power delivered by the panel.
I have a web site that explains this in more detail, but the site rules say I can't post it here :(

I would need to know what regulator you are picking to know if the power supply you found would work. Mine is a 24v supply but that is matched to my Redarc unit.
Cheers
Jason
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FollowupID: 788416

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