Car alarm & Solar panel

[c955]

As some may recall, I drive my car only occasionally. As a result of this, my car gets used about once every fortnight. To try and help the 6 month old battery stay tip top, especially with a passive immobiliser on the car, I hook up a small solar panel to trickle charge.

Unfortunately, 4 weeks standing was enough to kill the car battery so it wouldn't start today

I'm wondering if I need a bigger solar panel as the one I have only outputs 1.5W at 17.5V.

The alarm is an aftermarket one, fitted when the car was first purchased in 1994. Does anyone know what sort of power a car immobiliser/alarm thing is likely to consume? There are no product specifications in the alarm's handbbok

 

[Dieselman]

Well it must be that the consumers are drawing more than the panel is putting in so you must need a larger panel.
The rating of 1.5w is in full sunshine, I think you will be lucky to achieve 30% of this with a photovoltaic panel as once the sun intensity drops the panel just drops right off.

So lets say you're getting 10hrs a day at average 0.5wh and an average output voltage of 12v (although maybe not), that's 5wh per day.
If over a 24 hr period the alarm/immobiliser uses more than 5wh the battery will deplete.
5wh/12 = 0.017A over the 24hrs.

 

[miro]

Well it must be that the consumers are drawing more than the panel is putting in so you must need a larger panel.
The rating of 1.5w is in full sunshine, I think you will be lucky to achieve 30% of this with a photovoltaic panel as once the sun intensity drops the panel just drops right off.

So lets say you're getting 10hrs a day at average 0.5wh and an average output voltage of 12v (although maybe not), that's 5wh per day.
If over a 24 hr period the alarm/immobiliser uses more than 5wh the battery will deplete.
5wh/12 = 0.017A over the 24hrs.

If the car is drawing more than 300ma (0.3A) then the current draw is excessive. Given that the car is the traditional hard wired version there are no sneaky modules which may stay awake. Would be worthwhile getting a current draw reading and working on the suggested 4X factor.

 

[c955]

Thanks - this is exactly the sort of responses I was hoping for - I've temporarily disabled the immobiliser (irony heh ) till I figure out how to fix this problem and even though the car battery was flat yesterday, a 40 mile jaunt seems to have fully brought it back to life.

Newbie's question: how/what do I need for a 'current draw reading'?

 

[television]

One thing to remember with an MB is that the internal cigar lighter socket is a key 1 only so that cant be used with a solar panel.

All MBs have a higher quiescent current unlocked than locked.

Malcolm

 

[Dieselman]

One thing to remember with an MB is that the internal cigar lighter socket is a key 1 only so that cant be used with a solar panel.

Good point.

All MBs have a higher quiescent current unlocked than locked.

Malcolm

Even the ones with air locks?
I appreciate this may be to do with the locking relay holding on when unlocked but wondered if it had to stay armed to keep the car unlocked once the air pump has stopped..

 

[Dieselman]

Newbie's question: how/what do I need for a 'current draw reading'?

An ammeter. Buy a digital multi meter and connect it in series with the battery.
You can buy a cheap meter for under a tenner and is a useful workshop tool to have.
You could then also measure the output current and voltage from the solar panel as well. Don't be surprised if it's pretty low..they need full sun to work well.

 

[television]

An ammeter. Buy a digital multi meter and connect it in series with the battery.
You can buy a cheap meter for under a tenner and is a useful workshop tool to have.
You could then also measure the output current and voltage from the solar panel as well. Don't be surprised if it's pretty low..they need full sun to work well.

That is the way to go, one snag with a multi meter is that care must be taken not to break the ciucuit when joining the meter in, otherwise the frain could stop.

To do this I use double leads on one connection on the meter,one has a clamp, the other has a probe.
Join the single lead from the meter to the clamp on the battery, undo the clamp bolt then put the probe lead from the double pair of the meter into the center of the battery post, slide the battery clamp up the probe and connect the clamp on the double pair on the meter to the battery post.

I will pick up a clamp and put up a photo later.

Malcolm

 

[miro]

One thing to remember with an MB is that the internal cigar lighter socket is a key 1 only so that cant be used with a solar panel.

All MBs have a higher quiescent current unlocked than locked.

Malcolm

THe W211 and Maybach are both sold with solar panels so I would go with those wiring diagrams and dock the panel to a connector which runs to the relevant wiring scheme as in OEM.

That is assuming that the project is to resolve the problem in the best possible way. Otherwise it would be a matter of getting as much panel and as much current as possible and hoping for the best.

 

[l5foye]

I was interested to read about trickle charging the battery. We have a no of vintage tractors,some 6v and some 12 v. In the past we have trickled charged the batteries and have found that it seems to hasten their demise. The so-called battery conditioners (ie those which are supposed to monitor the condition of a bettery and charge as necessary) seem to have the same effect. What seems to work best is disconnecting the batteries and every so often turn the engines over. I would have thought that a battery in good condition should be able to start a car after 4 weeks provided the alarm is not drawing off more current than it should be. A bigger solar panel is not the answer,imho.

 

[c955]

Got a voltmeter ordered - should arrive in a few days. Can someone explain what I need to do with it to get useful info. about the state of my electric/charging system please?

I got in touch with the manufacturers of the alarm system and they reckon it consumes 18mAh. I presume this means it 'draws' 0.018 x 24 = 0.432 Amps per day?

Over 30 days, that would be 30 x 0.432 = 12.96 Amps. Ummm...what do I do with that bit of info.?

 

[BTB 500]

I got in touch with the manufacturers of the alarm system and they reckon it consumes 18mAh. I presume this means it 'draws' 0.018 x 24 = 0.432 Amps per day?

Current (consumption) is measured in mA, not mAh. If your car battery is 75 Ah capacity a current of 18 mA would take 75/.018 hours to discharge it ... that's nearly 6 months! A new lead/acid battery 'self discharges' (without any load) at about 3% per month, btw.