Amperage Draw for Toyota MH

[Bodybagger]

I had a bad experiece bringing the TMH home on the maiden voyage. I left town at dusk and bam! The battery would not charge. I planned on stopping and using jumper cables to periodically recharge the Toy's battery by jumping off the escort vehicle's charging system. This didn't work very well and we limped to a motel.

Fast forward to today.

I was recharging the AC system with good old R-12 and tested the amperage draw of the AC compressor clutch as a routine check (too high and it will likely burn up soon). While I had my AC/DC clamp on meter out, I decided to check total current drain of the electrical system under various conditions (lights on, lights off, etc) to see what I was up against that fateful night.

Engine running ONLY=8 amps

(This is the combined load of fuel injection, fuel pump, ignition system, and engine control computer. Absolutely nothing else was on. This is the bare minimum to keep the motor going.)

Engine running + headlights and taillights=22 amps

Engine running + headlights, taillights, and running lights=30 amps

Engine running + headlights, taillights, running lights + AC on with fan on high=41 amps

This DOES NOT include charging current to either of the batteries.

So it seems that if you have a 60 amp alternator, and it's hot and dark out, you have only 19 amps available to charge both batteries and run the radio, electric fridge, reading lamps, etc. This may be enough, but it's cutting it close. Particularly if you are recharging large batteries.

So I suppose I am going to eat my words and say that if you want a heavy duty alternator with greater capacity, that probably is justified. Also, a good case could be made for LED running lights, brake lights, and taillights.

Also, if you have to beat it with a bad alternator, keep in mind you are going to get a LOT further before your engine dies using 8 amps than using 30.

[WME]

Most people sleep at night and drive to the new location in the daytime. So figure somewhere 8-20 amps need for the drive. That leaves you with 40 amps for battery charging. In a couple of hr of driving your fully charged. Using LED lighting and running light is good your battery has less drain on and will charge sooner even with a stock alternator

Remember even if you have a 160 amp alternator you can only safely charge a battery at about 13% of its rated capacity. On a 27 sized battery that's about 14 amps.

The only reason to have a 160 amp alternator is if you have a very heavy load, like an electric winch or your running some monster inverter to run your house A/C off your 12v system going down the road.

As usual your opinion may vary

[Tom W]

This is when a generator comes in handy, or if there's a full moon I did that for about 10 miles one night every time I turned on all the lights it would start to cut out, this was out in the country no traffic, anyway made it home.

[Gulfstream Greg]

I thought a clamp on amp meter only worked corectly with Alternating Current. If they work on Direct Current thats a new one for me! http://en.wikipedia.org/wiki/Current_clamp

[ChairmanMeow7]

I went back to a stock one. After reading this I am wondering if I should have hunted around for another HD one.

But , as far as the coach battery goes , I have been told that a marine battery is designed to discharge slowly , but also designed to charge slowly as well. It would not like a big high amperage current going to it , trying to charge it up quickly. And hopefully the 15-20 amps left over for charging (at night) will be sufficient to keep both batteries charged.

Has anyone had a problem with a stock alternator keeping their batteries charged ?

[Gulfstream Greg]

I went back to a stock one. After reading this I am wondering if I should have hunted around for another HD one.

But , as far as the coach battery goes , I have been told that a marine battery is designed to discharge slowly , but also designed to charge slowly as well. It would not like a big high amperage current going to it , trying to charge it up quickly. And hopefully the 15-20 amps left over for charging (at night) will be sufficient to keep both batteries charged.

Has anyone had a problem with a stock alternator keeping their batteries charged ?

If you are cranking out 160 amps you better have a big wire coming off that alternator. The load on the engine would be tremendous. A battery will only accept so many amps into it when its low so bigger is not always better. AGM batteries can accept a higher amperage charge though. Think of a wire as a pipe. The bigger the pipe the more amps you can get through it. So to get high amperage to your coach battery and converter fuse block you would need to run some really big wire from the alternator to the isolator then to the coach battery. Something like 00 gauge. Like the size that runs from your battery to your starter. I would stick with the stock alternator.

[Tom W]

I have a fluke 36 thats clamp on ac or dc, as one said bigger isn't always better with electrical everything has to be resized.

[Gulfstream Greg]

I have a fluke 36 thats clamp on ac or dc, as one said bigger isn't always better with electrical everything has to be resized.

I think I am going to have to get one of those! My Fluke only measures AC current through the jaws. Have you put it side by side with an ampmeter?

[Tom W]

I used the AC at work a lot it compared with others the DC I used on portable equipment I was close enough for what I was doing. Fluke also makes a AC/ DC clamp Mod 80i-410 on the can be used with a Multimeter the price is a little high as with everything with fluke. The models I mentioned I've had for a long time so they might have changed.

[Tom W]

I forgot to mention if you measuring something thats a very low amp reading, add a length of wire wrap it around one of the jaws I go about ten time's then divide the reading by 10, for instance checking a laptop 35-60 watts, we used to do this to check crankcase heaters to make sure they were working on refrigerant compressors.

[Bodybagger]

I thought a clamp on amp meter only worked corectly with Alternating Current. If they work on Direct Current thats a new one for me! http://en.wikipedia.org/wiki/Current_clamp

The DC ones use the Hall Effect.

The one I've got is http://www.sears.com/shc/s/p_10153_12605_0...%26+Accessories and the only problem I have with it is that it's not a true RMS meter. In fact, today I was soldering some stuff in in a gate controller on site and I was using my inverter to power the soldering iron and I measured the voltage at the inverter... this meter read low at 104VAC while my true rms meter read 114VAC. Oh well, for 50 bucks on sale, I suppose I will sacrifice accurate measurement of AC votlages with harmonics. Maybe one day I'll get a true rms AC/DC and sell my half dozen other meters.