Where is the gel battery located in relation to the vehicle=20 battery? If the two batteries are located close to each other, will=20 the vehicle charge temperature compensation that is already in place=20 for the vehicle battery also be accurate enough for the gel battery? Is your gel battery of the AGM style? If so, the charge=20 characteristics should closely match the vehicle battery. dwayne At 08:13 AM 6/13/2017, Van Horn, David wrote: >On the subject of batteries in vehicles, I'm nearing completion of=20 >the installation of my radio gear in my new vehicle, and I am=20 >looking for a commercially available device that would properly=20 >maintain a small gel battery. > >Conditions: >Keep the battery fully charged from the vehicle supply when the=20 >motor is running. This pretty much eliminates anything lacking a=20 >boost converter. >Don't draw current from the vehicle battery when the motor is not=20 >running. Sensing alternator ripple or just battery voltage is fine. >Disconnect secondary battery from the load when the secondary=20 >battery is exhausted. Adjustable threshold is a plus. >Manage charge for the secondary battery so as to maximize service life. > >Anticipated load is about 300W maximum, typically in bursts of 10 to=20 >60 seconds, with about 25W as the "constant" load. > >http://ki0bk.no-ip.com/~pwrgate/LLPG/Site/LLPG.html Does not say=20 >how they achieve battery charging. >http://www.westmountainradio.com/product_info.php?products_id=3Dpg40s=20 >Pretty much states that the secondary battery charging is done=20 >through a diode or FET from the vehicle battery without regulation >http://www.nfarl.org/kits/powerGate/Power_Gate_Assembly_Instructions_v2.pd= f=20 >Really low end implementation > >My objection here is that the charge voltage for the gel battery is=20 >not the same as the vehicle battery, and simply tying them with a=20 >resistor or similar will likely result in the gel battery failing prematur= ely. >Charge times will be protracted with the circuit in the last=20 >implementation, and it continuously loads the vehicle battery with=20 >the secondary battery and radio system. > >So have you guys seen something better out there? > >-- >David VanHorn >Lead Hardware Engineer > >Backcountry Access, Inc. >2820 Wilderness Pl, Unit H >Boulder, CO 80301 USA >phone: 303-417-1345 x110 >email:=20 >david.vanhorn@backcountryaccess.com > >-- >http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >View/change your membership options at >http://mailman.mit.edu/mailman/listinfo/piclist --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA 780-489-3199 voice 780-487-6397 fax 888-489-3199 Toll Free www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .