[RE-wrenches] combining 24v and 12v systems

Thu Jan 2 15:37:24 EST 2020

I would like to add that you don’t need to get rid of the 12 v battery bank, but use it for the high amp draw buffer, like a large capacitor. Then use the DC to DC converter between the two battery banks. Done this for years on multiple off grid systems.  

Chris Worcester

Solar Wind Works

NABCEP PV Installation Professional

Office 530-582-4503

Cell 530-448-9692

www.solarwindworks.com

chris at solarwindworks.com

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Tom Duffy
Sent: Wednesday, January 01, 2020 8:55 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] combining 24v and 12v systems

Agree!  use a Victron DC to DC Converter

Kind regards

Tom Duffy

Senior Solar Design Engineer

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From: RE-wrenches <re-wrenches-bounces at lists.re-wrenches.org> On Behalf Of Allan Sindelar
Sent: Tuesday, December 31, 2019 6:51 PM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Subject: Re: [RE-wrenches] combining 24v and 12v systems

Agreed: no 12v tap. I’ll add (with modest experience, as this doesn’t come up as an upgrade very often any more) that Mean Well, despite the odd name, proved itself pretty reliable in some early Wattsun tracker drives and some other DC-DC applications. Available online; see https://www.meanwell-web.com/en-gb/dcdc-converters/

Allan

On Dec 31, 2019, at 10:46 AM, Dan Fink <danbob88 at gmail.com> wrote:

I second everyone. Center-tapping a 24 or 48v battery bank for 12v SEEMS like it should work just fine, especially for low load infrequent use like a 12v water pressure pump for a greenhouse, a weather station, etc.. Nope, I've been a loser every time, with that battery or pair always the first to go bad.

Samlex and Victron both make DC-DC converters I have had good luck with; they are thermally protected and you can stack multiple units for more amperage.

Dan Fink

Executive Director, Buckville Energy Consulting

NABCEP PV Associate

NABCEP Certified PV System Inspector

IREC Certified Instructor™ for: 

~ PV Installation Professional

~ Small Wind Installer

NABCEP Registered Continuing Education Providers

d <mailto:dan.fink at greendustrialtraining.com> anbob88 at gmail.com

970-672-4342

On Tue, Dec 31, 2019 at 10:57 AM Ray <ray at solarray.com> wrote:

Even with battery balancers, battery tapping is still a really bad idea.  I know, I did it on my own system in the 90s.  The DC/DC converters are the way to go, but be sure and over size it by a fair amount to handle the fridge starting surge.  Unfortunately my favorites are no longer available: made by Solar Converters in Canada. I've seen them last decades.  Iota should be good stuff, their chargers have long term reliability.  Samlex inverters have been around for quite a while too, but I don't have long term experience with their converters.  

Ray Walters
Remote Solar
303 505-8760

On 12/31/19 10:05 AM, Dave Angelini Offgrid Solar wrote:

Tapping a battery bank is not a good practice. it will unbalance the bank. Much better to add a 24V electronic converter for the 12V loads. Then replace the 12V loads when time permits. They will need a spare converter so buy 2. Amazon has tons of these converters. Your quote is great BTW. H N Y !

Dave Angelini Offgrid Solar
"we go where powerlines don't"
http://members.sti.net/offgridsolar/
e-mail  offgridsolar at sti.net
text 209 813 0060

On Tue, 31 Dec 2019 11:52:20 -0500, Chris Schaefer  <mailto:chris at solarandwindfx.com> <chris at solarandwindfx.com> wrote:

G'day and Happy New Year to All, 

Recently came across this offgrid OB FX system. The first part is a 12v battery system w/ 2 PV modules, 2 Trojan L16  batteries used to power a frig and freezer about 6 years old. The second is a 24v with 3kw of PV, 4 Trojan L16's, twin OB FX inverters installed by an HVAC contractor back in 2016. This was their first offgrid project. Oh boy, lol. The client would like to add more battery capacity to both. My thought here is since we are powering only a 12v frig and freezer why not simplify the system by creating a single battery bank and then tapping off of the 24v bank using proper fusing and creating a 12v buss? Admittedly I live in a 48v world so I'm asking our esteemed colleges as to options on how to address this. 

Oh yeah, the installer is unresponsive (no surprise there) and they are also having firmware issues with an old Mate 3 and would like me to install a new Mate 3s but that's another issue I'll tackle when I head out to site. 

Thanks All,

Christopher- 

Chris Schaefer's
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