Rather than use the term 'isolator' which is often confused with a diode-steered device, I use Automatic Charging Relay, Voltage Sensing Relay or Combiner/Separator. The benefits are:
- Its automatic and therefore convenient.
- It can protect your alternator from abruptly seeing an inordinate load.
The cons are:
- ACR & VSRs manifest in a number of wiring schemes according to the individual manufacturer. Many of these schemes are suitable for preserving the starting battery against drain while using instrumentation (chart plotter, fish finder, GPS, etc) that draws very little current. These schemes often contradict what is really needed for large audio system usage. You'll note that ACR/VSRs are not usually used in circuits applicable to trolling motors which closely parallels a large stereo at rest.
- Oftentimes, low voltage will keep the relay or solenoid from closing or staying closed which results in a lack of alternator charge and deeper cycling which reduces the stereo battery lifespan. An ACR/VSR makes an AC shore charger essential.
- None of the ACR/VSR manufacturers have a scheme to facilitate the use of an AC shore charger. They expect two battery banks to be charged via a single-bank charger or the ACR/VSR stays closed with high voltage thereby circumventing the individual battery bank profiles and charge program.
- ACR/VSR schemes must be flexible to fit the system size. There isn't a single prescription that fits all systems. As the stereo current draw increases, and as battery amp/hours increase and depending on the size of your alternator, your design should be altered to fit the situation.
- Many of the ACR/VSRs are dual-sensing rather than using a directional priority charge system. And this dominoes into additional complexities.
- In most cases you have to supplement an ACR/VSR with some form of switch or additional relay to provide a.) emergency bypass, b.) AC charging isolation and/or c.) elimination of small current draw while the boat is in storage. Again, it differs with each system.
In summary, my take is if you're doing it on the cheap or you don't have the tolerance for the added technical issues then just stick with a simple switch. Know when to connect the stereo bank to the alternator in order to strike a predetermined balance between preserving your alternator or extending your battery(s). Keep in mind I'm still a major advocate of an ACR/VSR if you're going to do it right.
I regularly talk to 'G' (Grant West). He has seriously changed his tune related to AC charging and no longer prescribes to using 'tenders'.
'Tenders' are fine for motorcylces, ATVs, UTVs, seldomly driven weekend cars, etc. They maintain starting batteries (not deep cycle) that are put into storage in a fully charged state. However, deep cycles that are seriously discharged are another story. Issues of desulphation are well cronicled everywhere. Check in with any boat dealer who sells tournement fishing boats. They don't use 'tenders' on trolling motor banks because the batteries don't last as long. Its not just about restoration speed.
David your right there, one should never hook any seriously discharged battery up to a tender and expect it to do the job regardless of what it's in. A tenders purpose is, as i said, is maintenance and not meant to restore any battery seriously drained. If one were to use a tender, like i do, i always make sure my batts are up to speed before connecting to the tender. And i do that by using the boat or i top them off with a higher amperage charger at home after. They're out of the boat off season and stay on a tender all winter out of the cold. Consequently i'm on year three with the same batts without issues with a personal best of four.
Originally Posted by EarmarkMarine
Now that being said i also do realize that some people load their boats up (just like cars, RV's, etc.) with all kinds of audio gear and goodies pushing the limits of the system and then have to make amends for doing so, like not paying attention to details like batteries but i also feel some of the stuff being added these days is just overkill too. Just my opinions, i learned years ago (dating myself) when batteries were nowhere near as good as now and AGM was a dream how to take care of them and make them last. Try running race cars and track trailers on deep cycles long term and see how long they last! ;)
12v 80amp relay hooked to the accessory position of the key switch is the way to go.
I second the relay but I would use the RV isolation relay for about $18 and wire it to the ignition with a disconnect switch. Keep the relay away from areas that may accumulate gas fumes. I don't think the hydrogen gas accumulation would be significant to prevent it from being mounted next to the batteries.