Double battery as a backup?
 

I have a Shabah 212Z with a single battery. Is it a good idea for next year to get another battery and a battery selector switch on board?

What type of battery or are they the same as car batteries.

J

Re: Double battery as a backup?
 

Here's a couple posts with good battery info.

One
Two

When I added my 2nd battery, I went with a Blue Sea ACR and would highly recommend it. Nice setup that you don't have to fiddle with switching back and forth.

Re: Double battery as a backup?
 

so if I use an ACR it looks like
each battery goes to the switch and the ACR and then a separate line to the motor and the last one goes to what? is that the CB panel?

Re: Double battery as a backup?
 

Our 1994 Davanti 205 is used by a variety of family members so when we decided to put a second battery in the primary objective was that no "operator knowledge" would be required. We installed a solenoid rather than an isolator and switch. This way both the deep cell house battery and the cranking battery are charged as needed with no action required from the operator .

This approach does require physical separation of the wiring however. We paid a local auto electric rebuild company about $250 to wire the Deep Cell to all the power outlets and components that are not part of the "engine" like radios, courtesy lights, anchor light and the like. The excellent design of the Mariah electrical system allowed this "re-wire" to be accomplished with very little modification to the original wire plan.

The cranking battery is now isolated from discharge by anything other than cranking the engine and it is charged automatically as needed. This is a more expensive approach but makes the entire electrical charging system automatic.

Re: Double battery as a backup?
 

The only problem with an ACR is this: Suppose you've been on the hook all day, enjoying the fun and the sun, and drained your house battery. (The "house" battery being the one that supplies everything but your starter system.) You start your engine (which is started off the starter battery). So far, so good. The ACR senses a high enough voltage on the starter battery and kicks-in to start charging your house battery. Guess what: Now your starter battery and house battery are connected. Since your house battery is drained, your starter battery will try to charge it. If, after a few minutes of this, your engine should die for some reason, you may find your starter battery has been drained by the house battery far enough to leave you dead in the water, anyway.

Admittedly an unlikely scenario, but it could happen. I understand some newer ACRs won't allow this to happen. I don't know which ones those would be.

A better option might be an echo-charging system, such as the one made by Xantrex. (Only problem with Xantrex is, from what I've been reading on the 'net, their customer service is absolutely terrible.)

Jim

Re: Double battery as a backup?
 

SEMIJim, not sure your description of the ACR (isolator) is accurate. By design it's diode configuration should only allow one way current flow. This prevents the problem you have envisioned. I am not an electrical engineer so may have my facts wrong; this is just my understanding of the diode type isolator. In my opinion the solenoid type separator is better than the diode type because the full voltage (no voltage loss from the diode's resistance) output of the alternator is transferred to the battery being charged.

Re: Double battery as a backup?
 

An ACR (Automatic Charge Relay) is not the same thing as an isolator. An ACR disconnects the house bank from the starting battery until, during charging, it detects a certain minimum voltage on the starting battery, then closes the relay, bringing the house bank on-line to the charging circuit.

Yes, that's how an ACR works.

However, it is my understanding that some ACRs are not prone to the potential failure mode I described earlier. (I'm not certain how.)

Jim

Re: Double battery as a backup?
 

The blue sea ACR won't join the batteries if they aren't within x volts of each other. I can't remember the low threshold but it seems like it was around 10v on the low battery. At that point, if you want to charge the low battery, you either have to put it on a charger or change to the combine mode on the switch, effectively bypassing the ACR.

I haven't seen or used the Xantrex so I can't vouch for it, but I can give the Blue Sea ACR a thumbs up :wink_thumbup:


10.8 volts is the low battery threshold. In 12v mode, if the low one is below 10.8, it won't combine them.
http://bluesea.com/files/resources/i.../990310020.pdf

Re: Double battery as a backup?
 

I installed a second battery and a switch. I use battery one for starting only, baterry 2 when on the beach for the stereo

Re: Double battery as a backup?
 

I just installed a twin installation with a BEP marine 'cluster' consisting of the intelligent split diode assembly, a master switch for each battery and an emergency parallel switch for both batteries. The cluster comes assembled and has got to be the easiest and safest ways to fit a second battery. Just follow the simple instructions and go. The intelligent unit ensures charging priority is given to the start battery, only when this iss fully charged does it begin the charge of the second battery. In practice, the unit will spend 90% of the time charging both. If you need to add a mains charger, just buy a twin output and attach to batteries downstream of isolation switches so that the system is isolated and your batteries can charge.