Better wiring, big difference

[markopolo-ClassB]

I recently added a new smart battery isolator ( http://www.classbforum.com/phpBB2/viewtopic.php?f=12&t=3576 ) using short runs of 4 gauge wire and for good measure I added an additional body ground ( http://www.classbforum.com/phpBB2/viewtopic.php?f=9&t=3573#p26314 ).

It warmed up to a bit above freezing today so decided to run the microwave oven in my van off the alternator to see if those two modifications gave any noticeable improvement in maintaining voltage etc.

A previous test ( http://www.classbforum.com/phpBB2/viewtopic.php?f=9&t=2668#p15768 ) a year and a half ago had these results:

The test was to run the microwave with the engine running at the three different idle speeds to see the affect on voltage. I combined the 2 house batteries, the 2 chassis batteries (4 batteries total) and the alternator for the test.

The voltage quickly dropped to 12.9 volts at each RPM setting. Each time I tested I ran the microwave for 20 seconds and I tested it 2 or 3 times at each RPM setting. The voltage recovered right away but was a little lower after each test. From 14.4v at the beginning down to 14v by the end.

I combined all battery banks using the old isolator, new smart isolator and manual marine type switch. The van was running at a cold idle around 800 rpm. Voltage displayed on the inverter was 14.7v. I ran the microwave oven on full power for 20 seconds and the voltage only dropped to 13.9v. So I did the test again with the same results but this time listening to the engine and I could hear the change in engine sound as soon as I started the microwave oven.

The third test was at 1,070 RPM and it produced the same results but with no change in engine sound. 13.9v, 910 watts at the inverter. 910W divided by 13.9V = 65 Amps. Immediate recovery of voltage to 14.7v as soon as the microwave oven stopped.

In the previous test a year and a half ago the voltage dropped to 12.9v. Booster predicted that there could be some wire size or isolator drop issues in my setup. This is with the stock CS144 124 amp alternator - probably 18 years old. I think the 1 volt gain is a big improvement.

Do you think the 14.7 volts is a problem or could it have been because the van and alternator were really cold - I didn't even warm it up for the test. All 4 batteries were fully charged - been plugged in all winter.

 

[booster]

That is good news. I wonder why your microwave pulls so many less amps than ours, which is at about 85 amps at 14ish volts?

I have limited experience with the GM alternators, but from what our stock DR244 (145 amp) did, I would say the voltage is just about what you would expect. We would always start at about 14.7 and then it would taper to 14.3/14.4v going down the road with low loads. If the loads were high so the alternator got hot, we would see as low as 13.9/14.0v. I think you are right where you need to be, but if you don't charge the coach through the diode isolator, you will be a bit high in voltage for the batteries on long drives. That is what got us started on putting in the manual disconnect, as we had the same voltage through a separator.

 

[markopolo-ClassB]

Thanks. That's good news re: the 14.7v being expected. I have an email in to Aopec to find out if I can disable the smart battery isolator when required.

The microwave oven in my van is only 600 cooking watts / 900 power consumption watts (both listed on the label).

 

[booster]

Ours is a 750 watt cooking power, so that makes perfect sense.

 

[mkguitar]

A microwave may be a variable load...I know that the panasonic unit in my home is...

if "testing" a more steady current draw could be a toaster or a space heater- once the heating elements get hot..about 30 seconds- they stay pretty steady

Mike

 

[markopolo-ClassB]

Just thought I'd update this topic also.

As Booster predicted, the voltage output of the alternator did drop as the alternator got hot from use. The 14.7 volts would drop to 14.2 volts from the alternator as things warmed up. I run my 3-way fridge off the inverter when driving and that would further drop the voltage down to 13.9 volts. That's a bit high for a "float" voltage on long drives if starting the journey with fully charged batteries but acceptable I think.

With the engine idling, I ran the microwave oven off the alternator while cooking meals and the voltage never dipped below 13.9v :thumbup:

 

[booster]

Just thought I'd update this topic also.

As Booster predicted, the voltage output of the alternator did drop as the alternator got hot from use. The 14.7 volts would drop to 14.2 volts from the alternator as things warmed up. I run my 3-way fridge off the inverter when driving and that would further drop the voltage down to 13.9 volts. That's a bit high for a "float" voltage on long drives if starting the journey with fully charged batteries but acceptable I think.

With the engine idling, I ran the microwave oven off the alternator while cooking meals and the voltage never dipped below 13.9v :thumbup:

Very nice, it is good to see the quite a few folks are getting good results with microwaves off of the inverter with the engine on. It is so much easier than the generator running, or knocking a lot of the batteries (assuming they are even big enough). That 13.9 volts is perfect with the micro on. 13.9 going down the road probably isn't a big deal, even if not ideal. You are still below the "gassing" voltage of wet cells, which is where most of the manufacturers start to worry most, even though it doesn't apply as much to AGMs. Most put the gassing voltage at about 14.1 volts.

Do you have any method of seeing if you are pulling anything from the batteries when the microwave is running? My guess from the voltage is that you aren't, but when we had the small alternator we would take about 10-20 amps of the power from the batteries. Ours is a 700 watt cooking power micro, maybe yours is a bit smaller, which would explain it, too.

 

[markopolo-ClassB]

Just updating this topic after completing some upgrades.

Before: 4 gauge to psw 1000w inverter
Now: 2 gauge to psw 1500w inverter

Before: 6 gauge on the A/B/Both/Off make-before-break switch for manually connecting the house & chassis batteries if needed.
Now: 4 gauge

Before: 6 gauge and 4 gauge to chassis ground (in addition to factory grounds)
Now: 1 gauge and 4 gauge (in addition to factory grounds)

Before: Inverter was not on the A/B/Both/Off make-before-break switch.
Now: All loads, including the inverter feed from the on the A/B/Both/Off make-before-break switch.

Now: 1 gauge wire to the Trimetric shunt.

Now: I shortened the 4 gauge wire on the automatic charge relay that connects house and chassis batteries when charging.

When the engine is running:
The original isolator is still in place. Maybe 6 gauge. The newer automatic relay is on 4 gauge. Only 3' or 4' because house and one chassis battery are near each other. I can turn the A/B/Both/Off make-before-break switch to Both and parallel another 4' run of 4 gauge. 1 gauge wire comes from the engine compartment to the second starting battery located behind the drivers seat. Basically I can have the equivalent of 1 gauge (maybe bit more) from the alternator to the house bank if/when needed.

Initial testing:

Fast idle on. 1,070 engine RPM, should be 4,012 alternator shaft RPM

Engine running
600W cooking / 900W power consumption microwave oven running.
Voltage
Trimetric: 14.2V
Samlex: 13.8V
Solar monitor: 14.1V
ScanGauge: 14.1V
0.6 amps flowing into the batteries.

Engine running
Heat gun on 1,000W setting
Voltage
Trimetric: 14.0V
Samlex: 13.5V
Solar monitor: 13.9V
ScanGauge: 13.9V
0.3 amps flowing into the batteries.

Engine running
Heat gun on 1,500W setting
Voltage
Trimetric: 13.6V
Samlex: 12.7V
Solar monitor: 13.3V
ScanGauge: 13.2V
9 amps and climbing flowing out of the batteries.

Also, after heating the interior of the van and the garage I have started the 5200 BTU air conditioner 4 times on inverter and battery power alone (engine not running). That seems to work fine. :clap:

After the initial testing I discovered a fuse was hot after running a 67 amp load trying to bring the volts down for a/c startup surge testing. It's a 175 amp ANL fuse between two short pieces of 00 gauge that leads to the A/B/Both/Off switch. I cleaned the lugs & used better fitting washers and that problem is solved. It doesn't even get warm now. :thumbup:

 

[booster]

Very nice results, Marko! Nice update and data.

 

[markopolo-ClassB]

I should note that is with the stock 124 amp alternator.

The not so good results prior to starting this topic made me think the alternator was old and maybe getting near replacement time. Turns out all I needed was the wiring upgrade.

I did get a new alternator back then but never installed it. Here's the performance curve chart for the alternator in the van and the new one on my work bench:



My guess is that with it being new and having a higher output I'd be able to get the full 1500 watts from the Samlex without drawing any amps from the batteries.

 

[booster]

I should note that is with the stock 124 amp alternator.

The not so good results prior to starting this topic made me think the alternator was old and maybe getting near replacement time. Turns out all I needed was the wiring upgrade.

I did get a new alternator back then but never installed it. Here's the performance curve chart for the alternator in the van and the new one on my work bench:

View attachment 3054

My guess is that with it being new and having a higher output I'd be able to get the full 1500 watts from the Samlex without drawing any amps from the batteries.

I would certainly agree with that assumption.

The 140 amp alternator must also be a somewhat different design type, also, as the amperage climbs much more quickly with rpm than the 124 amp one, which is really good for our kinds of use.

 

[markopolo-ClassB]

Should be over 100 amps available for battery charging if I install the new alternator.

With the latest wiring upgrade it looks like I've lost the ability to drop the voltage to 13.9V on long drives with already charged batteries by simply running the fridge on AC.

It's time to add a switch to interrupt the small gauge ground wire to the Aeopec relay. That should take it offline when desired. The old isolator is still in place so that should provide a more float like voltage in that circumstance.