<html><head></head><body><p dir="ltr">Then that is not a "ground". It is a DC power supply common / negative.</p>
<p dir="ltr">In automotive systems, these are at the same potential, because the battery negative is tied to the vehicle chassis. In marine systems, they must be isolated. The consequence of this is that the potential of both battery terminals can then float with respect to the safety ground - the potential difference is instantaneously indeterminate. This is referred to as "common-mode" voltage, as both positive and negative DC rails float at the same time, so that their difference is constant. Your installed equipment will likely have a common mode voltage rating (or if not a rating, it still has a physical limit) beyond which it cannot insulate between one of the power terminals and the safety ground, which is at earth potential. One possible solution to this is to tie the power supply common (battery negative) to the hull / earth ground as in an automotive system, but to do so through a very high resistance, such that the battery gains a reference potential, limiting the
common-mode drift, but will still not permit a short-circuit current to flow in the event of e.g. connecting your positive battery terminal to the hull. My preference is to maintain complete isolation, but if that corrects the problem it is diagnostically useful.</p>
<p dir="ltr">Assuming that there is no continuity between either supply terminal and your actual "ground" (the hull), I would check the polarity as you suggested, and also check the open circuit resistance of both devices at their power supply inputs.</p>
<p dir="ltr">Sean<br>
</p>
<br><br><div class="gmail_quote">On June 9, 2016 7:26:35 AM MDT, hank pronk via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<table cellspacing="0" cellpadding="0" border="0"><tbody><tr><td valign="top"><div>The compressor ground goes to negative on battery and compressor chassis is bolted to the hull.</div></td></tr></tbody></table> <div id="_origMsg_">
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Sean T. Stevenson via Personal_Submersibles <personal_submersibles@psubs.org>; <br />
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Personal Submersibles General Discussion <personal_submersibles@psubs.org>; <br />
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Re: [PSUBS-MAILIST] wiring problem <br />
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Thu, Jun 9, 2016 12:32:18 PM <br />
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<table cellspacing="0" cellpadding="0" border="0"><tbody><tr><td valign="top"><p dir="ltr">Just to confirm - when you say "compressor ground", you are referring to the chassis / safety earth (which should be connected to the hull) and not the power supply negative (which should not be)?</p>
<p dir="ltr">Sean</p>
<br clear="none" /><br clear="none" /><div class="yqt1290766698" id="yqtfd88240"><div class="gmail_quote">On June 9, 2016 6:18:35 AM MDT, hank pronk via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex;">
<div style="color:#000;background-color:#fff;font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:12px;"><div id="yui_3_16_0_ym19_1_1465473702416_4811"><span>Hi Alan</span></div><div id="yui_3_16_0_ym19_1_1465473702416_4810"><span>Yes that is how it is wired.</span></div><div id="yui_3_16_0_ym19_1_1465473702416_4810"><span><br clear="none" /></span></div><div id="yui_3_16_0_ym19_1_1465473702416_4810"><span>Hi Sean,</span></div><div dir="ltr" id="yui_3_16_0_ym19_1_1465473702416_4810">The radio works perfect, well I assume, I should say it turns on fine as long as the compressor ground is disconnected. When I turn the radio on with the compressor ground connected the radio breaker trips. The breakers in Gamma are an aviation style breaker, they look like what you have in you house breaker panel. If I remove the radio from the hull, I can turn it on just fine with the compressor ground connected. I am
wondering if my radi!
o is
shorting out so there is pos current in the cabinet and the compressor is providing a ground for it to short out.</div><div dir="ltr" id="yui_3_16_0_ym19_1_1465473702416_4810">I will instal the transducer and do some more testing, I can put the surface radio transducer on top of the sub transducer and test to be sure the radio is actually working still. </div><div dir="ltr" id="yui_3_16_0_ym19_1_1465473702416_4810">Hmm now I am wondering if I have the power reversed on the compressor and I am turning the sub into a positive ground, the compressor should still work with polarity reversed. </div><div dir="ltr" id="yui_3_16_0_ym19_1_1465473702416_4810">Thanks' guys.</div><div dir="ltr" id="yui_3_16_0_ym19_1_1465473702416_4810">Hank</div> <div class="qtdSeparateBR"><br clear="none" /><br clear="none" /></div><div class="yahoo_quoted" style="display:block;"> <div style="font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande,
sans-serif;font-size:12px;"> <div style="font-size:16px;"> <div dir="ltr"><font size="2" face="Arial"> On Wednesday, June 8, 2016 8:26 PM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<br clear="none" /></font></div> <br clear="none" /><br clear="none" /> <div class="y_msg_container"><div id="yiv0080695068"><div><div dir="ltr">Hank, do a continuity check between battery negative and the hull / chassis / safety ground. There should be no continuity from either battery terminal. If there is, the DC power supply common is tied down to chassis at one of the devices. Check the radio antenna as a possible culprit.</div>
<div dir="ltr">Next, check the potential of each power supply connection, not only between + and - at the device, but with respect to each other as well. (You mention tapping 24 V off a 36 V battery - any chance you're between +24 and "0" on one device and +36 and +12 on the other?)</div>
<div dir="ltr">What is the breaker type?</div>
<div dir="ltr">When you say it doesn't work with a ground wire connected - you are referring to a hull connection?</div>
<div dir="ltr">Sean<br clear="none" />
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<br clear="none" /><br clear="none" /><div class="yiv0080695068gmail_quote">On June 8, 2016 4:12:21 PM MDT, hank pronk via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="yiv0080695068gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex;">
<div class="yiv0080695068yqt0258577304" id="yiv0080695068yqt94241"><div style="color:#000;background-color:#fff;font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:12px;"><div dir="ltr" id="yiv0080695068yui_3_16_0_ym19_1_1465423436941_4229">Today I was doing some final wiring and discovered if my hp compressor has the ground wire on it, my acoustic radio trips the breaker. What the bleep is going on? Nothing is grounded to the hull anymore. I am taking 24V off a 36V bank for the compressor and the Radio is also taking 24V from the same source. </div><div dir="ltr" id="yiv0080695068yui_3_16_0_ym19_1_1465423436941_4229">Hank</div></div></div><div style="margin-top:2.5em;margin-bottom:1em;border-bottom:1px solid #000;"></div><pre class="yiv0080695068k9mail"></pre><hr /><br clear="none" />Personal_Submersibles mailing list<br clear="none" />Personal_Submersibles@psubs.org<br clear="none" /><a rel="nofollow" shape="rect"
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