![]() ![]() With this in mind was thinking that I could use whats left above the knee voltage to drive a transistor into saturation and the current through that to in turn close the relay - something like the following diagram. then If I connect a 13V zener diode from the starter battery pos to one side of relay coil, the other side back to battery neg (via suitable resistor to limit coil current).Ĭonnected directly across the aux battery will be my inverter so it receives power whether the ignition is on or off.Īm I correct that once the alternator charges the starter battery past 13V and the zener reaches breakdown and connects the two batteries in parallel the ongoing output of the alternator should prevent the auxillary battery from dragging the starter battery down to it's discharge level?ĭoes this all sound plausible or am liable to end up with fried electricals or a flat starter?Įdit: apparently I was mistaken in my assumptions of zener behaviour and didn't account for the voltage drop across the zener at breakdown. In addition, Victron Energy products limit the initial surge current which assists in avoiding welding the relay contacts on the battery. Was thinking I could leave the starter battery as is, connect negative of aux battery directly to starter negative and connect both pos terminals using a normally open 150 amp relay. This combo is what I would buy were I going to do it again.I'm putting together a bare bones dual battery system for the car so I can run an inverter from the second battery while the car is off. ![]() A dual sense relay will allow solar or any other charge system connected to the house battery to charge the starting battery once the house battery is fully charged.Ĭan buy an ACR/VSR in combination with a marine battery switch so that you can force the two batteries to be paralleled or even switch the starting chores to the house battery if need be. to charge the 'house' battery last it will never turn on when the solar panel has charged the 'house' battery. With a single sense relay set up to allow the alt. Single sense relays only sense the voltage from one side. There are two versions of the ACR/VSR's, single sensing and dual sensing. Relays also disconnect when the charge voltage drops, be that because you turned the engine off or there was some large draw on the starting battery. to charge both at the same time, even when they are not at the same state of charge. to first bring the starting battery back up to full charge before connecting the 'house' battery to charge it. The Automatic Charge Relays and Voltage Sensing Relays (different names for essentially the same product) don't have any voltage drop and do something that the diodes can't. I prefer to use a robust marine battery switch for those needs. I don't buy the marketing for those semi-automatic relays that have a remote switch. The constant duty solenoids pre-date the diode isolators and are still a better option though the automatic relays are better still. There are constant duty solenoids (BIG relays) and there are automatic relays. Unless the alternator's voltage regulator monitors the voltage, ideally, at the battery, or not quite as ideally, downstream of the diode isolator the batteries will never see a full charge. so it kind of depends on what you want, if you want it just like a camper, and don't want to worry about switching or forgetting then Diode would be best for you.ĭiodes have a small voltage drop. I did this when I turned off the truck and built the suspension for a couple weeks, before realizing I left it on the WVO tank and just that little bit wasted the battery.īut always, the Simple turn switch under the hood is the simplest and least (basically no extra) wiring.Įdit: As well with a Diode you can't use the batt except for auxiliary stuff, won't help winch, start the truck ect. Does that make since? so always closed will more then likely be "off" on your cab switch so if you leave your cruiser for a week or two you don't drain your batt. Just make sure you wire the relay the way that is least likely to wear your batt down wile the switch is on. Either a big manual switch/ isolator (you can get like 400amp ones and HB for cheap) Or the relay route so you can control it in the cab. I am about to do my double battery on mine and I am going to do it the way it did it one my other vehicles. Diode = voltage drop, hard time fully charging specially with the cheaper ones. ![]()
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