Parasitic Load?

[Benckj]

I have plenty of toys in my car including pumps, indicator lights, wideband, EBC, ECU, seat heater,etc, etc. Because of all these and car tends to sit for weeks without being run I installed a high capacity battery which is something like 730cca and 70ah capacity (Exide premium).

Recently the battery tends to die within a week so after charging overnight with a 3 stage smart charger I checked the parasitic load on my circuit off battery positive terminal to be 85ma. This seems high to me but not overly excessive given the toys which have a direct battery input. By my calcs at this load the battery should last 34days although may not have enough power to start engine.

After recently replacing an alternator in my 96NA I was surprised at the corrosion and broken terminals on the rectifier diodes. Although alternator checked out OK it wasn't going to survive much longer so I replaced.

My question; what is an acceptable parasitic load on an OEM circuit and can alternator internal faults contribute to this value?

[Gleshlich]

Following this post. I have a fluctuating drain in mine between 2 and 5 AMPs when off. I have a battery cutoff switch for the time being until I figure it out

[Benckj]

Probably wouldn't be a bad idea to install cut off switch in mine. Guess the only thing I'd lose is radio station memory which I hardly use and have the hassle of popping frunk before using car. It wouldn't be too bad if I could locate isolator in decent place. Where did you install?

[Gleshlich]

Have mine in the frunk. Bottom right corner. Make sure there's nothing rolling around in there as it could get interesting with a battery cutoff mid corner

[Benckj]

My frunk is getting rather cluttered with the installation of my WI system (pump, accumulator, pressure switch and gauge) plus I store spare tyre, tools, fuel can and blanket there. Will look at the possibility of installing an isolator switch up around the brake master cylinder so frunk items can stay put when switch is used. I'd rather find the problem but I think it will be a long and hard job of testing and isolating each circuit. Might even see if I can get battery replaced under warranty as its only approx. 1.5 years old. Need to punch up my details as I registered it on-line.

[Benckj]

Correction, battery is a XN50ZZMF Exide Extreme rated at 730cca and 85ahr rating and installed March 2015. Has a 3 year warranty but I might just confirm this as had to register it on-line to get extra year.

[Malcolm]

I'd defintely start by load testing the battery to make sure it is still in good condition.

Sounds like you have a lot of things receiving a supply from the battery that don't really need it. Perhaps you should consider moving them to ignition-switched supplies? Anyway if they're at least fused it is very easy to identify what is drawing current; just connect your ammeter and pull fuses one by one, watching the current draw to see if any trigger a significant drop. If you end up with an empty fusebox and the draw is still there, then the permanent supplies need to be looked at - which from memory should only really be the starter motor? IIRC even the alternator is connected to the battery via a (very large) fuse

[GDII]

I'd defintely start by load testing the battery to make sure it is still in good condition.

Sounds like you have a lot of things receiving a supply from the battery that don't really need it. Perhaps you should consider moving them to ignition-switched supplies? Anyway if they're at least fused it is very easy to identify what is drawing current; just connect your ammeter and pull fuses one by one, watching the current draw to see if any trigger a significant drop. If you end up with an empty fusebox and the draw is still there, then the permanent supplies need to be looked at - which from memory should only really be the starter motor? IIRC even the alternator is connected to the battery via a (very large) fuse

That would be my method too.

Like you said, the starter motor is the only thing connected directly to the motor that isn't fused. It doesn't even have a fusible link. The alternator is connected almost directly to the battery but it has a fusible link at the battery and the 120A ALT fuse. But to get that out you have to unbolt it from the fuse box. Almost everything else has a fuse that can be pulled out.

[Benckj]

All my circuits have fuses and generally switched supply via a relay. Several items do have a direct connection to battery but should not draw any power. The EBC, GPS tracker and turbo timer are examples.

I've load tested the battery using a decent 7 stage charger and it has passed. Next step is to bring into Exide dealer and let them test capacity. I think they run with a figure of 80% listed CCA to pass. Did find out the warranty is for 30 months so good thing I checked as if not registered on-line its only 24.

[Benckj]

The alternator is connected almost directly to the battery but it has a fusible link at the battery and the 120A ALT fuse.

Back to my orginal question; what is the normal OEM parasitic load on battery and can the alternator contribute to this if some diodes are shot?

[GDII]

The alternator is connected almost directly to the battery but it has a fusible link at the battery and the 120A ALT fuse.

Back to my orginal question; what is the normal OEM parasitic load on battery and can the alternator contribute to this if some diodes are shot?

I'll do a test on my car but watching a video it says 50mA is max. Not on the MR2 though.
My car only has the alarm and aftermarket stereo head unit so no really abnormal draws should come from mine. My battery will last months without being used so my system is probably a good one to test this.

This is a good video for people who aren't familiar with what to do as a reference. I know this doesn't apply to you Jim as you know electronics very well.

[Benckj]

I'd be interested to know what yours is Phil. I didn't find the 85ma exceptional which is why I'm surprised my battery is falling short every week. Granted this was only a spot check and could vary up and down based on battery voltage levels and ambient temperatures. I might just check my 96NA so I have something else to compare it with although there are many differences between the two vehicles including the remote key entry on my turbo which is stock.

I will leave in car until weekend and if its dead again it will be time to pull out and bring in for testing at Exide depot. Not much sense in re-conditioning if I can get a replacement under warranty. Looking at buying a new 130amp alternator Stateside to replace my stock 90amp one. Will cost approx. $260NZD delivered. Not a solution to the problem but its something I should have done when I dropped engine 2 years ago. Hope to do a decent road trip later this year.

[Gleshlich]

I suspect my drain is an alternator diode too. Easiest way to check would be to unplug the alternator and check the current draw with battery disconnected.

However, since your draw is quite low it may just be the battery. There are battery shops all over the country that do free health tests. You just have to drive in

[Benckj]

Took car for run into town last night and it started and ran fine. Starting to think my 85ma may be normal background load given all my electronic goodies. Would like to know if this load remains constant as sometimes battery seems to drain quicker than other times. I wonder why it would change and how can I monitor? A mounted amp gauge would certainly help but would have to be fairly course to cope with run time current (ie 100amps). Might look into what is available.

Something like this would work although I'd rather have a CT clip on for current measurement. This one is good for 0-100amps and has resolution to 0.01.

https://www.aliexpress.com/item/5pcs-Re ... 6fb3deddc8

[GDII]

Well that failed. My multimeter has a blown 10A fuse so I can't do the testing. I wonder what I did either this time or a previous time for it to blow...