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Charger/isolation	Reply
by WW5AA on September 12, 2008	Mail this to a friend!
I am replacing my APRS in the car with a full blown system. A laptop with WiFi, PK232, IC-V8000 running on a second battery. I will be installing a charging/isolation kit in order to run the system with the engine off. Doing a Google search brings up isolation kits for 60 amp alternators ranging from $20 to $300! I do not mind paying for what I need, but do not want to spend money on what I do not need. I will be using a 12 volt, 55 amp/hr sealed lead acid as the second battery. Any thoughts or recommendations? 73 de Lindy

RE: Charger/isolation	Reply
by K0BG on September 12, 2008	Mail this to a friend!
A couple of things. If you go to my web site and look under Alternators & Batteries, you'll find some information on isolators. The main problem with cheap isolators is the fact they're just diodes, so the voltage drop can be as much as 1.2 volts under load., and a minimum of .5 volts. The way around this is to use one with a built in FET switch like the Hellroaring unit has. The FET shorts out the diode, and has just .1 volt of drop across it. You can use relays, but that add a level of complexity, and about 4 times the headaches on the long run. As for the battery, if it is inside the vehicle, you should used an AGM, and not a sealed SLI battery. One last problem you're liable to encounter, and that's turning on the Check Engine light. Most late model vehicles read the voltage and current out of the alternator to adjust the injectors based on load, etc. If you suddenly connect a second battery that is at a charge level far removed from the SLI, the sudden change in alternator current will cause the ECC to turn on the Check Engine light. ' Alan, KØBG www.k0bg.com

RE: Charger/isolation	Reply
by KB1LKR on September 12, 2008	Mail this to a friend!
Use Shockey diodes in the isolator for lower voltage drops if you don't go with a commercial isolator?

RE: Charger/isolation	Reply
by K0BG on September 12, 2008	Mail this to a friend!
Schottky (note correct spelling) diodes do indeed have lower forward voltage drop in small signal applications. However, those used in high current applications have only slightly less FVD (.7v) than silicon diodes (1v or so), and they are much more expensive. Alan, KØBG www.k0bg.com

RE: Charger/isolation	Reply
by WW5AA on September 12, 2008	Mail this to a friend!
Thanks guys, I should have known you would have it on your site Alan! My forgetter is working better than my rememberer these days (:-) 73 de Lindy

RE: Charger/isolation	Reply
by KB1LKR on September 13, 2008	Mail this to a friend!
Thanks Alan. I'm always mixing [Walter] Schottky & [William] Shockley -- and the respectively named semiconductor devices -- up with each other!

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