Question about installing Aux battery just for starting

[rouxel]

So, I was thinking about adding another battery solely for starting my l300 in the cold Edmonton winters as I drive it daily.

Right now I have 2 batteries under the passenger seat but I am still having trouble starting it.

My question:

Can I just add a third battery in a battery box just behind the seat and simply install directly to ONLY the starter and alternator? Also plan on putting battery blanket on it so it's warm at time of start.

I think I have a power drain somewhere right now as my van had lots of trouble starting the next morning. Batteries die quite quick.

I don't really want to do a isolator if I don't have to. I want this battery to have no connection to the others what so ever. I do lots of ice fishing and other winter adventures in remote areas where a boost may not be available as well as to work and back everyday (no plug in at work) so I'm looking for over kill. I'm fine with the third battery behind the seat.

Thanks

Travis

[Growlerbearnz]

I have a similar setup in my delica, except with only two batteries, and I use a voltage sensitive isolator relay (VSR). One battery is connected to the starter and glow plug relays, the other battery to everything else. When the voltage of both batteries drops below 12V the relay separates them, preserving the starter battery while allowing the "everything else" battery to go as dead as it wants.

One issue I found was that the computer that controls the glow plugs is powered from the "everything else" battery- meaning that if that battery died, I couldn't start anyway. To get around that I installed an emergency start relay which switches everything else to the starting battery, but a switch/button that operated the glow plug relay manually would achieve the same result.

Concerning your proposed setup:

You're still going to need an isolator. If your third battery is connected to the alternator, and the other two batteries are also connected to the alternator, then all your batteries are connected together. You can't use a basic diode isolator on our alternators either, because the sense wire is connected internally to the output wire and your alternator won't start charging without a battery connected directly. I'd suggest this one: http://www.amazon.com/Smart-Dual-Batter ... 00400IYTK/

I'd start by looking at why your L300 is difficult to start even with two batteries (Yes, I know, Edmonton, but still...) After any obvious power drains (you've checked for interior lights left on, a new stereo or alarm, haven't you) the most common fault with dual battery setups is mismatched batteries: one of the batteries being older than the other, or a different brand or size. A failing battery will drain the good battery until they're both flat.

If one fails you should replace both, but no-one ever does because it seems expensive- but it's a false economy. Try and get your replacement batteries from the same batch- check the serial numbers are close.

If your batteries are mismatched and you can't afford to replace both, then an voltage sensitive isolator is your next best bet. That way if one fails it won't drag the other one down with it, and you can still jump start from the good one.

[rouxel]

I really don't want to be the guy that takes shortcuts to save money and compromise safety but with my job relying heavily on oil and my gf being out of work right now I have to be as tight as possible.

Could I just put the battery on a switch? Manually isolate the battery and just beak the connection every night. I can get a switch from work for free.

Travis

[Growlerbearnz]

Sounds like a switch is the way to go. But check your existing dual battery setup too- it would be a shame to let one failing battery destroy a good battery. Maybe put the switch between the two batteries so one is protected- and keep your third battery charged in the trunk along with jump leads, just in case?

[Growlerbearnz]

Another thought- if you had *two* switches you could have 2 batteries isolated, with the third one running your radio overnight. Switch on the backup batteries in the morning and off you go.

We're talking about huge-ass switches here, right? 150A at 12V? The starter and glow plugs draw a LOT of current.

[rouxel]

How would I test to see if I have something draining my power? I just bought the van a few months back and don't know what the old owner may have wired in to draw power. I do know that he put in a glow plug override switch and a inverter but other then that I'm not too sure. Always started fine in the warmer weather.

Travis

[rouxel]

Another thought- if you had *two* switches you could have 2 batteries isolated, with the third one running your radio overnight. Switch on the backup batteries in the morning and off you go.

We're talking about huge-ass switches here, right? 150A at 12V? The starter and glow plugs draw a LOT of current.

That's what I originally wanted to do but I just not confident in my skill level to do that type of work. I'm not overly familiar with car electrical.

Anyone in Edmonton available to help a guy out on a Saturday? Haha. I have a huge heated shop.

[Growlerbearnz]

To check your resting current draw you need a multimeter set to Amps. Connect the multimeter between the + battery terminal and the battery clamp, so that all the power now runs through the meter (Red positive lead of meter to battery, Black negative lead of meter to battery clamp). DON'T turn on the ignition- the meter can't pass enough current to run the engine and will catch on fire.

Most cars draw less than 30mA (0.03A) of power at rest. If yours is drawing more, then start pulling fuses until you figure out which accessory is causing the excessive power draw.

I'd suspect the inverter, they can be power hogs. Is it powered on all the time? Even if you don't have a multimeter, try pulling its fuse tonight and see how you go. Anything else that has power when the ignition is off is a suspect too. Interior lights, radio, alarm, clock?

If you eliminate everything that's drawing current and the battery *still* goes flat, then it's probably one bad battery dragging the other one down.

[rouxel]

I had a clamp meter handy and set it to 40 amp dc. While there was no wires in the clamp it was reading 0.83 and after I put the group of wire off the positive terminal it was reading 1.11 amps.

[Growlerbearnz]

I'm not sure how accurate those clamp meters are at the low currents we're talking about here. Showing a reading when not attached to anything would make me suspicious. 1.1A is excessive, but it's about 12W- the same as, say, an interior light (10W) plus the "door ajar" lamp (1W) in the instrument cluster.

[Firesong]

Putting a third in is excessive. 2 proper batteries should be enough. You may be having a problem with the connections , one of the batteries or both or maybe your alternator.