{"title":"Voltage Sensitive Relays (VSR)","description":"\u003cp\u003eA voltage sensitive relay is a switch that watches voltage.\u003c\/p\u003e\u003cp\u003eThat is all it does, and for a lot of setups that is enough. When the starting battery rises above a set voltage, which in practice means the alternator is charging it, the relay closes and the auxiliary battery joins the circuit and takes a charge. When the engine stops and the voltage drops, the relay opens and the two batteries are separate again. The fridge runs the auxiliary flat and the starter is untouched.\u003c\/p\u003e\u003cp\u003eIt is the simplest way to run a second battery, and it is the cheapest. No charge profile, no display, no settings. It still needs cable sized to the current, protection at both battery ends and an installation that follows the relay's own instructions.\u003c\/p\u003e\u003cp\u003eThe limit is that it passes on whatever the alternator gives. On an older vehicle with a fixed-output alternator feeding an AGM, that is usually fine. On a modern vehicle with a smart alternator that drops its voltage to save fuel, the auxiliary never sees a full charge. And on a lithium battery, which wants a specific charge profile and a controlled current, a relay is the wrong tool.\u003c\/p\u003e\u003cp\u003eFor those, a DC to DC charger is the answer. For a straightforward AGM second battery on a vehicle that charges properly, a relay does the job for a fraction of the cost.\u003c\/p\u003e","products":[{"product_id":"hardkorr-50a-12v-dual-battery-voltage-sensitive-relay","title":"Hardkorr 50A 12V Dual Battery Voltage Sensitive Relay","description":"\u003cp class=\"p1\"\u003eSet up your dual battery system easily with Hardkorr's battery box and this Hardkorr Voltage-Sensitive Relay (VSR) Kit. The VSR acts as an isolator, allowing the auxiliary battery (which is inside the box) to charge directly from the crank battery while the alternator is producing at least 13.2V, i.e. when the engine is running. When you turn off the ignition and the battery voltage drops below 12.8V, the VSR automatically cuts the link between the auxiliary and crank battery to prevent it from being over discharged.\u003c\/p\u003e\n\u003cp class=\"p1\"\u003eNOTE: This product is not suitable for vehicles with a variable-voltage alternator OR lithium batteries. Please check with your vehicle manufacturer prior to purchase if you think your vehicle may be equipped with a variable voltage alternator.\u003c\/p\u003e\n\u003cp\u003e \u003c\/p\u003e","brand":"Hardkorr","offers":[{"title":"Default Title","offer_id":42628269146284,"sku":"HAR-HKPBATTVSR","price":38.0,"currency_code":"AUD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0598\/1129\/9500\/files\/hardkorr-50a-12v-dual-battery-vsr-voltage-sensitive-relay.webp?v=1710995194"}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0598\/1129\/9500\/collections\/hardkorr-50a-12v-dual-battery-vsr-voltage-sensitive-relay_4db652d9-4f23-4754-8871-2d8ff2a6ed64.webp?v=1741668394","url":"https:\/\/roamgear.com.au\/collections\/voltage-sensitive-relays-vsr.oembed","provider":"Roam Gear","version":"1.0","type":"link"}