I advise not to "center tap" the 24v battery, with a Voltmaster or any other "half to half" balancing unit. My own Voltmaster failed to maintain the two halves at a sufficiently close state of charge. It's hard enough to keep the cells working well as team without adding possible additional imbalance issues.<br>
<br>Wattage requirement for a DC SunFrost is small enough that a "not too expensive" DC-DC converter can be connected in series between battery and the lower voltage DC load. My $0.02 US.<br><br clear="all">Mick Abraham, Proprietor<br>
<a href="http://www.abrahamsolar.com">www.abrahamsolar.com</a><br><br>Voice: 970-731-4675<br>
<br><br><div class="gmail_quote">On Wed, Oct 7, 2009 at 8:11 AM, Bob-O Schultze <span dir="ltr"><<a href="mailto:bob-o@electronconnection.com">bob-o@electronconnection.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div style="word-wrap: break-word;">Allan,<div>First, depending on the age of that Sunfrost, it might be OK to use on either a 12V or 24V system directly. The older ones are 12V only, but I'm not sure when the changeover occurred. An email to Sunfrost should give you that data.<br>
<div>For over 15 years we've used a Vanner Voltmaster. Don't know if they are even available anymore and you need to have a battery system that you can tap at 12V into equal sections. Basically, they look at both halves and switch from one to the other based on a very small voltage imbalance. In the 98% efficient category. The Voltmaster will be way more money than your other choices and needs two CBs on it's input rather than one, but if max efficiency is more important than initial cost, they are hard to beat.</div>
<div>Bob-O</div><div><div></div><div class="h5"><div><br><div><div>On Oct 6, 2009, at 10:04 PM, Allan Sindelar wrote:</div><br><span style="border-collapse: separate; font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><div link="blue" vlink="purple" lang="EN-US">
<div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri,sans-serif;"><span style="font-size: 12pt; font-family: 'Times New Roman',serif;">Wrenches,</span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri,sans-serif;">
<span style="font-size: 12pt; font-family: 'Times New Roman',serif;">Simple question, I know: what has worked well as a 24V – 12V DC-DC step-down converter for a Sun Frost? I am doing a design to completely rebuild/replace an early-90s off-grid 12V system with a new system at 24V. The only DC load is a Sun Frost. I think it’s an RF16, so dual-compressor. I know of at least three converters: Solar Converters; BZ Products; ICT; and I’m sure there are many more. What has worked well, with minimal ghost load?</span></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri,sans-serif;"><span style="font-size: 12pt; font-family: 'Times New Roman',serif;"> </span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri,sans-serif;">
<span style="font-size: 12pt; font-family: 'Times New Roman',serif;">Thank you,</span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri,sans-serif;"><span style="font-size: 12pt; font-family: 'Times New Roman',serif;"> </span></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri,sans-serif;"><span style="font-family: 'Times New Roman',serif;">Allan Sindelar</span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri,sans-serif;">
<span style="font-size: 10pt; font-family: 'Times New Roman',serif;"><a href="mailto:Allan@positiveenergysolar.com" style="color: blue; text-decoration: underline;" target="_blank"><span style="color: blue;">Allan@positiveenergysolar.com</span></a></span><span style="font-family: 'Times New Roman',serif;"></span></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri,sans-serif;"><span style="font-size: 10pt; font-family: 'Times New Roman',serif;">NABCEP Certified Photovoltaic Installer</span><span style="font-family: 'Times New Roman',serif;"></span></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri,sans-serif;"><span style="font-size: 10pt; font-family: 'Times New Roman',serif;">EE98J Journeyman Electrician</span><span style="font-family: 'Times New Roman',serif;"></span></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri,sans-serif;"><b><span style="font-family: 'Times New Roman',serif;">Positive Energy, Inc.</span></b></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri,sans-serif;">
<span style="font-family: 'Times New Roman',serif;">3201 Calle Marie</span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri,sans-serif;"><span style="font-family: 'Times New Roman',serif;">Santa Fe, New Mexico 87507</span></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri,sans-serif;"><span style="font-family: 'Times New Roman',serif;">505 424-1112</span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri,sans-serif;">
<span style="font-size: 10pt; font-family: 'Times New Roman',serif;"><a href="http://www.positiveenergysolar.com/" style="color: blue; text-decoration: underline;" target="_blank"><span style="color: blue;">www.PositiveEnergySolar.com</span></a></span><span style="font-family: 'Times New Roman',serif;"></span></div>
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