Hot Positive Terminal Running Electric CR A/C

[tsuter]

Originally Posted by mysocal911

Sorry that it appears that way.

Yes, you can charge the upper 12V battery externally when the vehicle is not driven,
but it must be continually charged or you'll only have 12V & not 24V after a short drive for the compressor voltage.
Remember, when the A/C system is operating the upper 12V is being discharged too, i.e. the alternator will only charge the lower 12V battery.
The 24V compressor will discharge both 12V batteries, which need to be continually charged.

It's true that you could design a "battery management system" to continually charge the upper battery,
but it must be capable of supplying the compressor current too. Would be a total Mickey Mouse system!

The alternator equally charges all batteries in the array...same as it charges all cells in the battery.... when in series you connect to the furthest positive and the furthest opposite negative for charging. Same as on the battery (6 cells at 2V) for 12V lead acid opposite ends. LiOn is 3.2V per cell and four cells = one 12V battery. Charged at one Positive and one negative opposite ends. The batteries in an array should all be the same.

Two 12V Lion batteries I mentioned will easily fit in the lead acid battery space...at less weight...

[mysocal911]

Originally Posted by tsuter

The alternator equally charges all batteries in the array...same as it charges all cells in the battery.... when in series you connect to the furthest positive and the furthest opposite negative for charging. Same as on the battery (6 cells at 2V) for 12V lead acid opposite ends. LiOn is 3.2V per cell and four cells = one 12V battery. Charged at one Positive and one negative opposite ends. The batteries in an array should all be the same.

Two 12V Lion batteries I mentioned will easily fit in the lead acid battery space...at less weight...

Don't think so! Draw a complete diagram that includes the 12V alternator with two 12V batteries in series.
Remember, the two series 12V batteries MUST be charged simultaneously to supply 24V for the compressor.
It's unfortunate we've been sidetracked.

From Jonny's post;

Ok, so lets use the serial/parallel 4 battery 'trick'. Where are they going to live? its a tiny car. The wiring would be pretty messy. On a technical note, all the batteries need to be the same type and age. What happens when the system ages? If there were lithium ion (to save weight), you'd need a BMS (more complication and expense). The 12V alternator would not cover the charging of the whole pack so that would need topping up. So on a long journey, the voltage would sag, probably to the point where the compressor will switch off...

[Nditiz1]

Ok so back to what I said just leave the system as it is and as tsuter said a terminal of 130-140 also fine. My 5 year optima is still going with having system on it for now 3 years.

[MikeD930]

Guys...can you drop the subject about 24V battery system? Plus I would not want to depend on battery powered A/C anyway. In my case the hot positive terminal was not caused by an A/C running off the battery. As I mentioned earlier...I was able to relocate the hot positive terminal away from the battery using the battery terminal adapter cable so the battery stays cooler while using the A/C. I will either replace the battery terminal with clean connections or add a new 2 AWG or 0 AWG wires from the alternator/starter directly to the A/C compressor cable which is connected to a positive terminal.

Originally Posted by Nditiz1

Ok so back to what I said just leave the system as it is and as tsuter said a terminal of 130-140 also fine. My 5 year optima is still going with having system on it for now 3 years.

You can add battery terminal adapter cable to move the stock positive terminal away from the battery which was what I did (in case you missed my earlier post about this). This will reduce the heat at the battery (instead of 120-130F it would be 90F). As someone said earlier...doing this relocates the 'heat sink' which was my intent.

[Nditiz1]

Thanks Mike, I see the post about the adapter. Didn't know you had already implemented the fix. Guess we can close this one out, thanks!

[mysocal911]

Originally Posted by MikeD930

Guys...can you drop the subject about 24V battery system? Plus I would not want to depend on battery powered A/C anyway. In my case the hot positive terminal was not caused by an A/C running off the battery. As I mentioned earlier...I was able to relocate the hot positive terminal away from the battery using the battery terminal adapter cable so the battery stays cooler while using the A/C. I will either replace the battery terminal with clean connections or add a new 2 AWG or 0 AWG wires from the alternator/starter directly to the A/C compressor cable which is connected to a positive terminal.

You can add battery terminal adapter cable to move the stock positive terminal away from the battery which was what I did (in case you missed my earlier post about this). This will reduce the heat at the battery (instead of 120-130F it would be 90F). As someone said earlier...doing this relocates the 'heat sink' which was my intent.

The key point being made is that without actually measuring current of the battery cable and current of the alternator cable, at idle (1K RPM),
one really doesn't know if there's a potential problem. It's actually a very simple test, and why wouldn't you do it to better understand your 12V A/C system?
It's not good for the battery to have an excess high current drain at idle.

[MikeD930]

Originally Posted by mysocal911

The key point being made is that without actually measuring current of the battery cable and current of the alternator cable, at idle (1K RPM),
one really doesn't know if there's a potential problem. It's actually a very simple test, and why wouldn't you do it to better understand your 12V A/C system?
It's not good for the battery to have an excess high current drain at idle.

One of these days I'll buy a current meter mainly for checking the current on my home HVAC and secondly for my car as you suggested. You keep beating on a dead horse saying that CR A/C has a big draw on the battery at idle causing high temp at the battery terminal. This is not what has been happening in my case. The CR A/C compressor will not run full capacity for long when it senses lower power input such as at idle. I would bring the engine rpm up with the throttle if I'm sitting at a long traffic light.

Seems you ignored my findings when I added the battery terminal adapter...

Positive battery terminal on battery:




Negative battery terminal on battery:

[phelix]

Thanks for posting those temperature photos. Can you also take one of the earth point that the compressor is using? I’m guessing it might be warmer than the negative battery post.

[Nditiz1]

Not to hash anymore or keep this thread going since it's already been resolved, but to close the questions of pull at idle.

0 draw while car is off - makes sense, well except on the two connected wires for clock, trunk light, radio
17 amps with Car on. Nothing on big red wire to compressor
27 amps with fan on full blast. Next to nothing on big red wire .11
~69amps with AC on. ~45 amps on big red wire to compressor
All was being at idle. RPMs had dropped off AAR down to ~900.

So yeah the amps don't look like overkill AND I have my configuration set to pull max amps all the time because I'm greedy.

[Joesmallwood]

Originally Posted by Nditiz1

Not to hash anymore or keep this thread going since it's already been resolved, but to close the questions of pull at idle.

0 draw while car is off - makes sense, well except on the two connected wires for clock, trunk light, radio
17 amps with Car on. Nothing on big red wire to compressor
27 amps with fan on full blast. Next to nothing on big red wire .11
~69amps with AC on. ~45 amps on big red wire to compressor
All was being at idle. RPMs had dropped off AAR down to ~900.

So yeah the amps don't look like overkill AND I have my configuration set to pull max amps all the time because I'm greedy.

To add, may ECUs have a input for "AC Idle Up". I set this up using MS3X so my car will idle up to 1100 when the AC is on. I have had zero issues with voltage drop since adding this logic. When the AC is off, my idle settles back down to my target of 975.

[Nditiz1]

Damn Joe that's awesome. Lowtech euro CIS here, no ecu once the car is up to operating temps it runs at 1100 with the AC off and around 950-1000 with it on.

[Joesmallwood]

Originally Posted by Nditiz1

Damn Joe that's awesome. Lowtech euro CIS here, no ecu once the car is up to operating temps it runs at 1100 with the AC off and around 950-1000 with it on.

I think 1000 is still fine/good enough, but I do like the feature of raising the idle when it's on. I wonder if there is some circuit mod that could be made to open an air valve in a vacuum line somewhere that would serve as "idle up", if it ever became a problem?

Anyway, it works as-is for me. So, good to go!

[Jonny H]

Originally Posted by Joesmallwood

I wonder if there is some circuit mod that could be made to open an air valve in a vacuum line somewhere that would serve as "idle up"?

Anyway, it works as-is for me. So, good to go!

Yes but you don't need any more circuitry - our ECU will do it for you. We have done this when we installed a system on a Volvo P1800 with twin SU carburettors. The problem with SU's is they need a certain amount of air flow or the engine will stall.

We fitted a solenoid operated EGR valve (from a modern Toyota IIRC) which leaked some air into the brake booster hose to raise the idle. We machined a brass bung with a hole in to regulate the amount of air leak and so adjust the idle speed. Think it ended up being about a 1mm hole to get a 150 RPM rise. We used the contactor output (grey wire) of our our ECU to control it so it only activated when the AC was on - no extra circuitry needed.

[Nditiz1]

Jonny - Im willing to try
Can you send over the steps in an email? Thanks!

[Jonny H]

Originally Posted by Nditiz1

Jonny - Im willing to try
Can you send over the steps in an email? Thanks!

You shouldn't need to do this on your SC. Just lower the 12.6 battery moderate threshold slightly in the ECU - 'balance' this with the idle speed.

On my car, in 38 deg C / 100F ambient, the alternator is producing 70-75A at idle and the car (with AC on) is using 80-85A ( just ignition, no lights or wipers). The battery is sat around 12.5 so not charging in this condition but of course, being at idle is a small part of any journey (we hope!). As soon as you move off, you get a good whack of charging from alternator so all is well.

Before I even started the AC project I noted that my SC with lights, wipers, defogger, stereo etc fitted with the standard 75A alternator sat at 12.3 volts at idle so wasn't charging either! The 75A standard alternator is only 35-40A at idle.

[Nditiz1]

Thanks I'll make that configuration change