Extending battery life

On 22 Jun 2006 06:39:40 -0700, "Griff" waffled on about something:

Hi Griff,

The first thing you need to do is to work out how much drain the "body electrics" are putting on the battery when the car is parked up.

A simple home multimeter should be able to measure this low current. Set the meter to amps/current Disconnect on side of the battery, and connect the meter between this lead and the battery terminal you just removed it from. (just don't try and start the car with the meter in line, or you'll melt it!). Sorry, but you'll have to reset the code on the radio after this. :-)

Once you have the standby current figure for the car, you can go about trying to find something to provide this current.

For example, if your meter says 1amp, and you have a 70AH (amp hour) battery, this means in a perfect world your battery should be able to last 70 hours. Although I wouldn't like to try and start the car by the 69th hour.

If the car take 2 amps, the battery will only last 35hours... Etc.

Most cheap solar panels I have seen that plug into the cigar lighter provide a pitiful current (in milliamps), which most modern car alarms would easily exceed, leaving you with a net drain on the battery.

Although having said that, there's nothing to stop you adding several panels together in parallel... Just remember, they'll have to provide all the current the car's going eat during 24 hours using the 8 hours of daylight in the winter time, so they need to provide 3 times the parked up drain current.

I suspect your 840 might start looking like one of those solar racing cars they race in Australia!

Simplest solution... Buy yourself a jump pack, which is basically a small 12 battery in handy carry case... You charge it up from the mains at home, and then put it in the boot. When you come back to a dead car, clip it onto the dead battery, start the car, disconnect the jump pack and remember the put it back on charge when you get home.

Something like this

Dodgy.

Don't feel bad -- I have a 7 series, and after 5 days of sitting; the battery is dead. I'd be happy for 10 days -- I disconnected the alarm / comfort locking and didn't gain much.

Personally - those two things don't bug me; at this point the radio code is second nature to me; and I think car alarms are mostly ignored by people; and a real car theif, or a smash & grabber doens't care about an alarm the later just grabs whatever and is gone; the former just disables the alarm quickly.

They could help; only one way to find out.

I use a battery-tender to maintain the battery when I put the bmw in the garage. It plugs into the cig lighter in the dash; I have it hanging from the ceiling; so I just open the door; grab it; plug it in; close the door -- not that hard, really.

The solar panel would help for "Not at home" storage, ala: airports, or hotel stays; but probably wouldn't keep it topped up indefinately.

I decided the radio code/car alarm issue was secondary to being "strandanded" (I often leave teh car where I can't use a charger for days) -- so I installed one of these, and was VERY pleased how nicely they work. Really amazing.

That said -- I think i'll be installing a solar panel (or two) on the back deck.

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No shit. Solar panels require SUNLIGHT. They're not powered by RAIN or DAMP so they're not much use in the UK.

In countries where it doesn't rain every 5 minutes the things are marginally usable but not real popular.

If parasitic load is killing two batteries in 8 days then that has to be the all time record parasitic load and does not sound remotely correct. A load that big can be measured.

Yeah I used to live there.

I carry one; becuase before I put hte pirority start gizmo in; that was what I was doing; but I've stopped carring it (it's still a lead acid battery that can leak.) since the gizmo has not left me stranded -- and jumping the bmw is a PITA and the electronics sometimes complains about it....

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"Richard Sexton" wrote

Just because it rains doesn't mean that there isn't sunlight. In fact, the parking meters in Seattle are solar powered; they power the printer and wireless (cell phone?) connection for credit card authorization.

FloydR

On Thu, 22 Jun 2006 15:13:32 +0000 (UTC), snipped-for-privacy@news.vrx.net (Richard Sexton) waffled on about something:

Yes Richard, we have no sunlight at all here in the UK. It just rains in the pitch darkness 24/7

:-p

Gawd knows who we stole this 70F sunny day from...

Dodgy.

Both batteries? You mean one at a time right? Neither of mine like bign left for a long time but often when I'm at the dealers I hear of people in 5-series whose batteries don't even last overnight - BMW solution: "leave the car unlocked overnight sir"

I dunno but they must have returned it as I can't see any blue in the sky from where I'm sitting.

Those work fine if they have enough output and if you park your car outside. You will want one with at least 1 sq ft of area, or two smaller ones. I've used these for a variety of vehicles that aren't used much, tractors to race cars. I love 'em. VW ships out every new car with a nice solar charger on the dash and connected so the cars arrive with a hot battery. Most dealers just pile these in the parts dept and sell them cheap. Ask your local dealer. I noticed Harbor Freight has a large solar charger now that puts out something like 5 amps for under $50. That is big enough to charge a dead battery in just a few minutes if you get stranded and are parked outdoors.

Get one that plugs into the cigar lighter. The jumper battery is also a good idea. They make some small ones that connect (and also charge) through the cigar lighter. Often all your battery needs is that little extra nudge to get your going, and you don't have to open the hood. If your car has a power outlet in the trunk, you can leave the jumper charging all the time.

OTOH you could try connecting the MM to the battery and lead with crocodile clips or similar, so the cars electrics are still being powered when the lead is taken off. Mike.

They're powered by light of any sort. Of course the greater the light the greater the output.

Contact BMW - in writing - and ask how long your model can be left safely without the battery going flat. I'd expect at least 14 days with a good battery in a good state of charge.

Dunno what happens on this model exactly, but many will take quite a high momentary discharge when the battery is re-connected and may take the fuse on the DVM. Best to disconnect one battery lead then connect with a jump lead etc with then connect the DVM in such a way as the jump lead can be removed leaving the DVM in circuit.

I have had this problem for a while now on my 5 series. Often I'll come back to the car in the morning and find the battery with not enough ooomph to kick it over. It bumps easy enough but that's hardly the point!

A jump pack sounds like a great idea but is that right.... leaving it unlocked reduces the drain?

Spain probably.

So I mover away and the sun comes out now? Figgers. Or maybe you're lying. I figure if I fly to London right now it'll be raining when I get there.

Besides I"m still trying to ge tmy head around Lucas solar cells. "they work ok but the die in the heat of the sun"

Unless not parked near an outlet I would try to use a auto charger like batteryminder of batterytender. They keep the battery full, and you don't have to bother with switching it off when full. They have quick connect terminals or you can use the cig lighter. Works great for my motorcycle. Haven't needed a new battery in years.

I agree, I use about 4 of them to keep my boat battery up, and a jet ski, and a couple of spare batteries.

On Fri, 23 Jun 2006 09:12:35 +0000 (UTC), snipped-for-privacy@news.vrx.net (Richard Sexton) waffled on about something:

Ah, a good old Lucas joke... It's the 1960's all over again! :-p

Gawd help us when you get to hear about Amstrad stereos from the 80s.

Dodgy