davidtan Posted November 16, 2015 Share Posted November 16, 2015 Hi Guys, My coach battery went out and i found the relay that I changed when I first got the RV did not work ( actually, i think it still works , but the rivet that grounds it is loose). But now that I think about it, Is this the correct way that the battery isolator is installed? I called the RV shops and it seems that they actually sell an actual isolator (not sure what the difference is). I know that the one I replaced is more of a starter relay and maybe shouldn't stay on the entire ride time. Any ideas? Quote Link to comment Share on other sites More sharing options...
zero Posted November 16, 2015 Share Posted November 16, 2015 Relays work better the rectifier-based isolators. For something that stays on all the time when driving - you are supposed to use a "continuous duty" relay and not a starter solenoid that is only rated for intermittent duty. They can look just the same. It is all in the specs. A starter "relay" AKA "solenoid" can draw 4-6 amps all the time, whereas a continuous duty relay will only draw 1-2 amps. Quote Link to comment Share on other sites More sharing options...
zero Posted November 16, 2015 Share Posted November 16, 2015 Here's one a NAPA. Also the top two in the sales flier from Surplus Sales. Quote Link to comment Share on other sites More sharing options...
davidtan Posted November 16, 2015 Author Share Posted November 16, 2015 I tried this one , but the wires got really hot. Quote Link to comment Share on other sites More sharing options...
WME Posted November 16, 2015 Share Posted November 16, 2015 The relay in the first post is a 4 wire unit. The 2 smaller terminals are +12v and ground. The mount is NOT the ground. Quote Link to comment Share on other sites More sharing options...
jjrbus Posted November 16, 2015 Share Posted November 16, 2015 The ground wire may be pull riveted to the firewall? Quote Link to comment Share on other sites More sharing options...
kayakthecoast Posted November 16, 2015 Share Posted November 16, 2015 This might be a good time to upgrade to a better system? I added a blue seas marine grade magnetic dual battery relay in mine with a dash rocker switch to combine or isolate starter and house batteries. Works great. Quote Link to comment Share on other sites More sharing options...
zero Posted November 16, 2015 Share Posted November 16, 2015 The relay in the first post is a 4 wire unit. The 2 smaller terminals are +12v and ground. The mount is NOT the ground. How can you ascertain that just from the photo? Having those two small posts does not automatically mean it has no ground for negative current. Many of those solenoids like in the picture had two small terminals because #1 was for positive engagement power, and #2 was an ignition-resistor bypass. That sort - used the ground based to receive negative current. You could take two solenoids side-by-side, and there would be no way of know which type it was. Not unless those little terminals are marked. If a ground-base type, one small terminal should be marked "S" and the other "I" (for ignition bypass). Quote Link to comment Share on other sites More sharing options...
zero Posted November 16, 2015 Share Posted November 16, 2015 For an example, here are two for Ford cars and trucks that are four-terminal and use the metal mounting base for a ground. Note the "S" and "I" markings on the small posts. Quote Link to comment Share on other sites More sharing options...
WME Posted November 17, 2015 Share Posted November 17, 2015 So you use Ford auto solenoids in your RV? ALL the 4 pole continuous duty RV isolators that I've seen use one of the small terminals for ground. There are 3 pole units that use the mount as ground. A loose rivet there would be a PIA. Quote Link to comment Share on other sites More sharing options...
Maineah Posted November 17, 2015 Share Posted November 17, 2015 Usually the 4 wire one's small terminals were crank + and neutral/park ground. Not likely to be continuous duty Quote Link to comment Share on other sites More sharing options...
zero Posted November 17, 2015 Share Posted November 17, 2015 The guy who started this thread clearly stated the relay is a starter-motor relay and not an RV type isolation relay made for full-time use. So yes, it could very be a "Ford" relay. Chevy, Dodge, and GMC rarely used that type since Prestolite, Chrysler, and Delco starters usually have a built-on-starter relay. Ford and Jeeps were known for having the little stand-alone relays. Subsequently many people call any relay that looks like that black plastic-cased unit - a "Ford" relay. Quote Link to comment Share on other sites More sharing options...
Maineah Posted November 17, 2015 Share Posted November 17, 2015 I tried this one , but the wires got really hot. It's a 30 amp Bosch light duty relay not heavy enough. Quote Link to comment Share on other sites More sharing options...
zero Posted November 17, 2015 Share Posted November 17, 2015 Usually the 4 wire one's small terminals were crank + and neutral/park ground. Not likely to be continuous duty If you are talking about 4-wire relays in general - there is no "usually" here. Many 4-wire relays certainly are made for continuous duty. Even some of those little Bosch plastic 50 amp units. And many automotive relays used to engage starter-motors in Ford and Jeep cars/trucks with four wires use the two small poles for "start" and "ignition." Especially if with breaker-point ignition. There are hundreds if not thousands of varieties of 4-pole continuous duty relays in use (two small poles are neg and pos for engagement). Quote Link to comment Share on other sites More sharing options...
payaso del mar Posted December 9, 2015 Share Posted December 9, 2015 go to defender.com (marine supply). they have at least 4 isolators (not repurposed starter relays), starting with the Yandina 100 amp for about $60. I figure marine grade stuff should last in RV use..... Quote Link to comment Share on other sites More sharing options...
linda s Posted December 10, 2015 Share Posted December 10, 2015 I spent 17 bucks for a Tekonsha isolator identical to the 20 plus year old one I took out. It will probably last longer than me. Fancy doesn't necessarily mean better Linda S Quote Link to comment Share on other sites More sharing options...
payaso del mar Posted December 10, 2015 Share Posted December 10, 2015 point well taken. i guess i'm used to marine stuff and maybe forget that it's overkill for land applications....no need for epoxy potted solid state unit for RV. Quote Link to comment Share on other sites More sharing options...
zero Posted December 10, 2015 Share Posted December 10, 2015 point well taken. i guess i'm used to marine stuff and maybe forget that it's overkill for land applications....no need for epoxy potted solid state unit for RV. There are many marine-grade full-time relays in the $20 price-range. The prices get silly high when people put them in boxes and sell as specialty items . . or . . when they package with a voltage-sensing chip attached. The chip costs more then the relay. Quote Link to comment Share on other sites More sharing options...
Maineah Posted December 11, 2015 Share Posted December 11, 2015 If you are talking about 4-wire relays in general - there is no "usually" here. Many 4-wire relays certainly are made for continuous duty. Even some of those little Bosch plastic 50 amp units. And many automotive relays used to engage starter-motors in Ford and Jeep cars/trucks with four wires use the two small poles for "start" and "ignition." Especially if with breaker-point ignition. There are hundreds if not thousands of varieties of 4-pole continuous duty relays in use (two small poles are neg and pos for engagement). Yes and every one of them use an isolated ground. If some one has a relay in their hand with 4 terminals from an auto parts store it probably is a starter relay the point here is don't buy a starter relay and if you want to make it simple buy a continuous duty relay with one small terminal. because the case is grounded to save you from having to ground the 4th wire. Quote Link to comment Share on other sites More sharing options...
zero Posted December 11, 2015 Share Posted December 11, 2015 Yes and every one of them use an isolated ground. "Every one" of what? There is no correlation between relays with 3 terminal versus 4 terminal when it comes to a relay being rated continuous or not. They come in many configurations. When it comes to auto parts stores - it depends on what you actually ask for. Go to NAPA and ask for a continuous duty relay and that is what you get. Ask for a starter relay for a Ford or Jeep and again - that is what you get. If anyone thinks they can ID the rating or type of relay they are looking at by how many terminals it has on it - they are asking for trouble. There are many relays available in auto-parts stores with four terminals and rated for continuous duty. Quote Link to comment Share on other sites More sharing options...
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