12V from 24V class panel - Page 1
Forum section: electronics / general

author: flywire
author_rank: Contributor
timestamp: November 27, 2020, 11:57:56 pm
content: Second-hand 24V panels from houses (egSTP190S-24/Ad+) are abundant and pretty cheap. What's the cheapest reasonable way of using them to maintain a small 12V camper battery system without hacking the panel?MPPT controllers cost much more than a second-hand panel and it's unreasonable to lose half the power with a 12V PWM controller.

author: Ian.M
author_rank: Super Contributor
timestamp: November 28, 2020, 12:25:36 am
content: Quote from: flywire on November 27, 2020, 11:57:56 pmIts only unreasonable if you've got limited area to mount panelsandorDIYing a controller will cost more than doubling the number of panels.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 28, 2020, 01:14:07 am
content: Build your own MPPT controller using a microcontroller.

author: flywire
author_rank: Contributor
timestamp: November 28, 2020, 01:32:16 am
content: Certainly panel space is limited and MPPT is not necessary. Halving the voltage, doubling the current and feeding through a PWM controller would probably be adequate.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: November 28, 2020, 02:17:55 am
content: Quote from: flywire on November 27, 2020, 11:57:56 pmwut?Are you lighting up a city?How many panels are we talking about? Can you devolve the size (W) of array, capacity of your battery and even your daily usage?

author: flywire
author_rank: Contributor
timestamp: November 28, 2020, 02:42:43 am
content: I linked a 190W panel and envisage 1 or 2 flat-mounted on a roof but some panels are over 400W now.Lighting is not the issue, it's heating and cooling. Hey, some people (Millennials ??) even like to run AC in their camper these days. lol

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: November 28, 2020, 03:46:13 am
content: Quote from: flywire on November 28, 2020, 02:42:43 amWell, I suppose the stereotypical millennial lounges around in air conditioned comfort with the temp setting up to +/- 20deg C away from outside ambient, so yeah, I suppose that would put a MPPT Solar controller out of anyone's price range.Can you provide more information on how much power the A/C uses?

author: flywire
author_rank: Contributor
timestamp: November 28, 2020, 04:54:45 am
content: 0W, I have no intention of running one. Now can we focus on using a 24V class panel like a 12V class panel?

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 28, 2020, 02:27:58 pm
content: You could build a buck converter with a fixed duty cycle and get close enough, but no reason to when you can do a proper MPPT.https://github.com/aplavins/Arduino-MPPT

author: flywire
author_rank: Contributor
timestamp: November 28, 2020, 08:56:14 pm
content: Hmm, that's where I'm at but that reference doesn't explicitly link the hardware, better to usehttps://microcontrolere.wordpress.com/2016/12/16/mppt-solar-charger/My question of using house panels is fairly common (eghttps://microcontrolere.wordpress.com/2016/12/16/mppt-solar-charger/comment-page-3/#comment-15327) and the standard response is it can be done, but the circuit needs to be reworked and calcs checked. That's beyond me.

author: flywire
author_rank: Contributor
timestamp: November 28, 2020, 11:37:20 pm
content: Seems theOSPControllergives MPPT on a house panel. It uses a DKP6012 buck converter interfaced with an ESP32." fails at cooling. The fan only turns on at 5A or above, and it can easily get toasty after hours at 2A. My solution is power the fan with a super cheap LM2596. It's a 3.0-40V to 1.5-35V voltage regulator that can also be used to power your ESP32." Realistically, the only optional thing in theBOMis probably the Power Meter.I'm not clear how it provides over-voltage protection from the solar array.

author: David Hess
author_rank: Super Contributor
timestamp: December 01, 2020, 05:32:56 pm
content: Quote from: flywire on November 27, 2020, 11:57:56 pmIf your 12 volt PWM controller has a buck inductor, then no power is lost beyond inefficiency.

author: flywire
author_rank: Contributor
timestamp: December 02, 2020, 07:13:37 pm
content: Quote from: David Hess on December 01, 2020, 05:32:56 pmI doubt any of those common cheap PWM controllers have a buck inductor.

author: tautech
author_rank: Super Contributor
timestamp: December 08, 2020, 02:10:37 pm
content: I'd advise you to treat such an installation with respect and invest in a decent controller.The pic below is of the capabilities of a single 320W panel charging a 12V system comprising of two 195AH SLA'a in parallel for a remote data link site.18A @ 14V is a good amount of power from 1.5m2 of silicon yet a moment before I snapped that screenshot the peak was 20A !

author: flywire
author_rank: Contributor
timestamp: December 10, 2020, 05:16:59 am
content: I'm not disputing the benefits of an MPPT controller that are clearly demonstrated by that report. Bear in mind the linked panel is 190W and your data on a 320W panel has about 70% more capacity but a portable system will most likely perform much worse. Now an essentially free panel with a controller costing over $100 is not such a good deal anymore.There's still a case for:* Open source controllers, egOpen Solar Project  Controllerwhich handles 12A using a buck converter and microcontroller for about $50* A  hacked panel converted to a 12V class with a PWM controller

author: Pineapple Dan
author_rank: Contributor
timestamp: January 28, 2021, 12:20:06 am
content: Quote from: NiHaoMike on November 28, 2020, 02:27:58 pmU have to be careful with those. That one has no reverse protection to stop current from battery to panel and he's driving two highside mosfets with the one IR2104 and no current sensorSee this thread I made a while back :https://www.eevblog.com/forum/projects/open-solar-mppt-charge-controller/msg1576591/#msg1576591That design has been around in various forms since the 2011 version by Tim Nolan. I made a couple of these that were no good because I made few changes to the design but the most recent one is working quite well. Still it isn't perfect as I still have some problems with ringing & lowside mosfet getting quite warm but should be out of the woods with next PCB.Tbh I had given up on ever getting a working DIY MPPT controller and tossed the project aside for years, not realising the design I was using was riddled with flaws. This would have been the deba15 one that's on hackadayThe microcontrolere.wordpress version would be based on the deba15, he got rid of the 3rd mosfet for reverse-blocking and put in a hefty schottky but probably wastes a few watts. Used a LTC4357 in my version and this works quite well but cost a couple € more.