Dashboard Solar charger

Submitted: Tuesday, Apr 28, 2020 at 11:40
ThreadID: 139954 Views:6192 Replies:4 FollowUps:11
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One more query on the ‘black magic’ spectrum for my ongoing search of knowledge on how things 12 volt function.

I have a habit of making assumptions of how these things work but as usual I am stumped and don’t want to destroy any gear in my experiments and seek the wisdom of EO as usual.

I have been given a small ‘dashboard solar charging panel’ complete with packaging but lacking ‘specifications’. This can probably be imagined by the name of the gadget: SMART - Solar Battery Charger - the ‘Smart’ being the producer. Yes, made in China.

I have set it up and clipped it to a couple of 12 volt batteries and metered the charge directly to the battery around 17 & 18 volts, depending on the solar energy available. Not bad for a small unit which I estimate is around 4 watts compared with my Jaycar 80 watt panel. It too produces about the same voltage.

My concern is that I know I need a regulator on the 80 watt panel when connecting to batteries because of the high voltage. The dashboard charger is designed to hook into a cigarette lighter to power up a flat starter battery using the vehicle cig lighter. So my questions is, although this is quite small, would the unregulated 17/18 v charge fry any equipment in a vehicle?

As far as I can determine I don’t believe it has destroyed the Breakaway battery or the old starter battery I have used for trialing, but that is an assumption. My estimate of 4 watts is based on the size = 5% camparison with the 80w panel

I hope I never have to rely on this to get me out of a serious situation, but am curious to know how effective it might be and whether it is worthy of ‘chucking it in just in case’ .

We live in hope of relief of our present travel restrictions. We are in the largest state, but we are limited to our home ‘zones’.

I might add that I have been plagued in the past with batteries letting me down purely from lack of equipment to maintain them, but now have adequate resources I believe. 300+ w solar on the van with two 100+ ah batteries and BC/DC charger off the vehicle generator. And the Ute has a BC/DC charger to the 2nd battery in the rear of the ute, which I can top up with the 80w solar panel when parked for a while.

Bit long winded but better you know the full circumstances rather than wonder.

In Edit I am unable to post the pic I meant to include. The thread just freezes each time I try.

Can post if needed.

Cheers - Phil
Phil 'n Jill (WA)

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Reply By: qldcamper - Tuesday, Apr 28, 2020 at 12:28

Tuesday, Apr 28, 2020 at 12:28
They are almost useless.
If it maintained 17 volts while connected to a battery then the battery must be either open circuit or heavily sulphated.
4 watts shouldnt raise the voltage much at all so I wouldnt think it would need a regulator.

Another major design error is that most cars have accessory supplied ciggy lighters which means you need the key turned on to connect it to the battery and the car would be using more than it is charging.
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Follow Up By: Member - Phil 'n Jill (WA) - Tuesday, Apr 28, 2020 at 12:40

Tuesday, Apr 28, 2020 at 12:40
Thanks Qldcamper.

It just occured to me I could switch the 80 watt panel from the No. 2 battery in the rear to the main battery. It has a regulator and can be clipped directly to the battery.

I would like to think that would't interfere with any electrickery in the system ... Phil
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Reply By: RMD - Tuesday, Apr 28, 2020 at 16:26

Tuesday, Apr 28, 2020 at 16:26
G'day Phil
If relying on such a device to actually charge a flat battery then, yes it will but probably take around 3 weeks, so if you wake and need a battery refilled, it isn't going to do it. As QLD says, for that unit to get to the battery it has to be direct and not through the ciggy plug as that does require the KEY/IGN turned on and the normal power usage items then switched on by the Key will far exceed the output of the little panel so the battery WILL simply go flat despite the panel connection.
The little panel is only 4 watts on a good day with everything in it's favour, normally quite a bit less.

To get a realistic reading, place your multimeter on amp setting and attach the panel (in full sun) and read the amp flow or rather sub amp flow. Max may be around 300milliamps , a good day reading. Significantly less than your 80w panel which probably produces around 55 watts on a good day. Even an 80w panel through a regulator will take a while to top up a flat battery. Seeing you have plenty of solar on the van, why not have a link cable from the van batteries direct to the vehicle battery so you can stuff a few electrons into the start battery IF required. Much quicker.

Just use the 4 watter for direct maintenance charge if needed. Through a small reg it will never over charge even a small battery, but many regs use a standby current simply to operate their circuits, You don't want it to use the majority or all of the little panels output otherwise nothing is gained.
Don't be taken in by the voltage you measured. Any panel will produce 17 or more volts, so no surprise there. It is the current at that voltage which is the wattage, Volts X Amps = Watts.
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Follow Up By: Member - Phil 'n Jill (WA) - Tuesday, Apr 28, 2020 at 22:13

Tuesday, Apr 28, 2020 at 22:13
Thanks RMD I see the point made by yourself and Qldcamper about the cig lighter and would opt for the direct battery link.

The van and vehicle are rarely parked close enough for a jump start, but prbably a good habit to get into when free camped.

If I did use the 80 watt panel to tickle it up I could always remove the regulator if the full 17/18 volts is not a threat to the battery system.

Cheers - Phil
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Follow Up By: qldcamper - Wednesday, Apr 29, 2020 at 07:25

Wednesday, Apr 29, 2020 at 07:25
Dont run the 80 watt panel without a reg.

Just buy a cheap flexable panel and reg and use that as back up with alligator clips if you ever need it.
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Follow Up By: RMD - Wednesday, Apr 29, 2020 at 07:50

Wednesday, Apr 29, 2020 at 07:50
I use an Anderson plug on a long heavy twin cable. If your van batteries are connected to an Anderson plug the cable can go to the vehicle. No need to be directly at the hitch. Then the van solar will charge the vehicle far quicker than an 80 panel can achieve. Seeing the dcdc reg of the van is running off the solar, it will dedicate all available solar energy at an elevated , BOOST level, to the cable and vehicle battery. Win win to me.
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Follow Up By: Member - Phil 'n Jill (WA) - Wednesday, Apr 29, 2020 at 11:51

Wednesday, Apr 29, 2020 at 11:51
Since the BC/DC unit was added along with the solar panels, I have noticed the power at the Ccaravan anderson plug is not 'two way' - it appears to only receive current from the vehicle alternator.

It does not allow me to 'tap into it' to power up the Engel like I used to 'pre-solar upgrade'.

I suppose this is to prevent 'drainage' if left connected whilst parked. We had the reverse of that problem in early days when the van fridge drained the vehicle battery during stops - until an isolator was fitted.

All very confusing.

Thanks RMD - regards, Phil
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Follow Up By: RMD - Wednesday, Apr 29, 2020 at 12:05

Wednesday, Apr 29, 2020 at 12:05
Hello again Phil.
No, the Anderson on the A frame will most likely connect to the DC DC units input and seeing itis totally isolated from the batteries being a switchmode device. You would require an auxiliary Anderson connected to the van batteries to allow the van DCDC unit, I presume also runs from solar, to deliver a charging ability to that AUX Anderson. Then to cable and vehicle battery via an additional Anderson direct on it's battery. The reason you may not be able to use the rear vehicle Anderson is its power is possibly cut off when vehicle is not running. Again not sure exactly how your gear is wired. Just assuming some normal items are present, ie, VSR etc. If a direct from the van batteries via the cable to the vehicle batteries, it will not only charge for emergency purposes but the van solar power will also run your vehicle electrics while driving if need be. ie, alt stopped charging, but with that connection all can continue. Emergency of course.

I can make my system do that if required.
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Follow Up By: Member - Phil 'n Jill (WA) - Wednesday, Apr 29, 2020 at 12:41

Wednesday, Apr 29, 2020 at 12:41
Thanks again, I will get the original solar installers to review the set up now I have switched vehicles, I have found auto electricians loathe looking at someone else's works - either that or its - ' Oh that needs to come out and we will put this other system in - $$$'

No argument from me - I can only find my way around a spreadsheet. :O))

Cheers - Phil
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Reply By: Batt's - Friday, May 01, 2020 at 01:24

Friday, May 01, 2020 at 01:24
I'm no guru on the subject but I would think any solar panel should have a regulator so you don't put to many volts through the 12v system. The regulator should be set to suit the battery type so it stays within the maximium safe charging volts for the battery but it's your risk if you don't use one which could get expensive if or when something fries. It's not worth the risk for the sake of spending $20 on a regulator.
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Follow Up By: qldcamper - Friday, May 01, 2020 at 08:17

Friday, May 01, 2020 at 08:17
Theoretically your correct.
Practically though i very much doubt that a 4 watt panel would ever raise the voltage of an automotive starting battery to a critical level especially if there is anything supplied by it that could be damaged by it.
Also IF it was possible to achieve such a level with only 4 watts it would take many more hours than there is sunlight in a day.
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Follow Up By: Batt's - Friday, May 01, 2020 at 13:28

Friday, May 01, 2020 at 13:28
No worries. I just thought that 17-18v whether it comes from a 4w panel or a 300w panel it's still 17-18v and beyond a batteries specs and it might cause damage to it or other electrical components it would be like a power surge regardless of the length of time.
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Reply By: Member - Andrew - Friday, May 01, 2020 at 13:49

Friday, May 01, 2020 at 13:49
Those little dash mount type panels were never originally supplied as a proper battery charger as they could never provide enough input current.

They were meant as a maintenance system to balance the standing losses of lead acid batteries as might be needed for vehicles not used for long periods. They were popular with boaties and farmers who used their motors infrequntly.
I have no information on how well they assist with Lithium batteries although I believe they do not have the same standing discharge issues.

They seem to be effective where there is NO draw on the battery but there effectiveness is reduced dramatically by incorrect orientation.

Being out in the open unattended can result in dust hurting their efficiency and leaving them on a dashboard is a problem with many vehicles windscreens and side windows filtering the sunlight sufficiently to render them ineffective.

Hope this helps and some of the tech experts may be able to clarify the physics.


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Follow Up By: Frank P (NSW) - Friday, May 01, 2020 at 13:56

Friday, May 01, 2020 at 13:56
"I have no information on how well they assist with Lithium batteries although I believe they do not have the same standing discharge issues."

Lithium (ie, LiFePO4 as used in recreational vehicles) batteries do indeed have a much lower self-discharge rate than lead-acid.

Also, they prefer not to be trickle charged in storage. They are best stored at about 80% SOC (it may vary with brand) and disconnected from all loads. That includes parasitic loads like dc-dc chargers, solar regulators, battery monitoring systems, inverters that go into standby mode and inverter-chargers.

If you leave those connected their combined drains will pull batteries down over time. For long term storage it is best to disconnect the battery negative, either by removing the cable from the battery or by using a simple manual isolator.

Otherwise, check the battery every few months and charge if necessary.


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Follow Up By: Member - Phil 'n Jill (WA) - Saturday, May 02, 2020 at 11:11

Saturday, May 02, 2020 at 11:11
I expect Andrew is right - I can think of a few applications where something in storage could do with a small constant feed during the day.

I also am cynical enough to realised a smartie will grab that idea and package it up as something it really isn't capable of.

Cheers all - Phil
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