Hey all,

I've been struggling since I bought my 07 Tundra back in March with its power system. I'm at my wits end and turning to you for help.

I've added 2 yellowtop optimas to a truckbox in the bed of my truck.

Cutting to the chase ... the 150A heavy duty alternator won't put out anything more than 13.8 volts, and most of the time it's more like 13.2. Charging additional batteries at 12.9-13.2 volts doesn't work unless I drive from here to Arizona every day. I really need 14.4 volts if I can get it.

1. I assume the Denso alternator has internal sensing. If the stock battery is low (12.2v without charging) or fully charged (12.7v) I still only see about 13.8 volts being output. Is this because it's tuned to only charge the stock battery?

2. I added an isolator from SurePower. This didn't work out since the alternator didn't sense the 1v drop and therefore the optimas never charged.

3. I removed the isolator and put in a battery separator from SurePower. It's a little better, but I still only have 13.2 - 13.6 volts to charge these optimas, and that's not enough for a high amperage charging.

4. I see a .2v - .3v drop from the front alternator to the back batteries, this is the 4 gauge wire. I am replace that with 0gauge wire tonight but that's still not going to get me more 14.4 volts.

Main Question: Why does the Denso alternator only like to output 13.2 - 13.8 ? Can I get 14.4? Can I remove the sense wire and give it voltage from the back batteries to help with it determining what to output? Can I put a resistor in the sense wire to drive up the voltage ?

The new 07 tundra is great, but I look stupid charging batteries in my driveway every day. Every other car on earth I've seen 14.4 volts coming from the alternator. If I remove my separator and put it back to factory, I still only see a max of 13.8 coming from the alternator. Is there anyone out there with an 07 tundra that can check the voltage for me ? Im wondering if the isolator fried my denso regulator somehow.


Please help : )

Sam


2.

Looks like std output is 13.2-14.8 Volts
(a) Connect a voltmeter and ammeter to the charging circuit as follows.
(1) Disconnect the wire from terminal B of the generator, then connect it to the negative (-) lead of an ammeter.
(2) Connect the positive (+) lead of the ammeter to terminal B of the generator.
(3) Connect the positive (+) lead of a voltmeter to the positive (+) terminal of the battery.
(4) Ground the negative (-) lead of the voltmeter.
(b) Check the charging circuit.
(1) Keep the engine speed at 2000 rpm and check the reading on the ammeter and voltmeter.
Standard current:
10 A or less
Standard voltage:
13.2 to 14.8 V
If the voltmeter reading is more than the standard voltage, replace the voltage regulator.

 

I'll follow '5.7rcbsb''s suggestion. I assume that's to check how many amps its drawing? I've amp clamped it and typically don't see it drawing more than 1-2 amps from the 2 back batteries, which during idle engine is probably just stereo stuff and the PC. I'll report back on that shortly when I can get the front tire off again to test... it's not an easy thing to get to : ) I did test the voltage right at the terminal at it was around 13.5 - 13.8 at the idle time. I'm thinking if I killed the stock battery so it had to recharge the sense wire would be giving less and it would up it's voltage, but havent tried that... that's next too.

Toxarch: I've got a minipc, routerboard, other radio equipment, gps, stereo, etc ... In the beginning I didn't want to mess with any factory stuff so I ran my own batteries for everything. I never wanted to be stranded on top of a mountain because I ran the test equipment for too long or something. With 240 RC I should be able to get that PC to run overnight in my driveway at least - as it stands the battery never charges fully and so it only runs for a few hours.

Thanks again for the help. I've worked with auto electrical in the past and never had such a hard time getting something like this to work smoothly. I mainly wanted to know if I'm crazy only seeing 13.2 - 13.8 on the alternator output (at idle or revving up, doesn't matter). It seems the only time I see 13.8 or so is right when I start it in the morning (colder?), otherwise its about 13.2. I can't remmeber for sure, but I thought the dash needle was in the middle when I bought the thing, but now it's 1-2 ticks to the left almost always. Is there anyone else willing to just put a volt meter to their battery while at idle to see if its 13.2 - 13.8, or 13.8 - 14.4 ? I'm starting to think my regulator is bad.

Sam

 

I installed a P3 brake controller in my CM. It has a troubleshooting option that allows you to monitor system voltage. You are correct, I've never seen it over 13.8V 13.5V is usually where it hangs out at. I too thought it was odd since my Civic would run at 14.4V

 

From a cold start 72* this morning 13.5v

Hmmm ?

 

do you guys have the cold package? just curious

 

I dont think so - no cold package that I know of... In Southern California. I'm guessing Toyota has done some tricks to try to get the battery to last longer by only trickle charging it or something. This is the first auto I've ever seen that doesn't produce enough voltage to fast charge a battery. The battery won't draw high amperage until it hits around 14v. I don't understand why this Tundra won't put out the juice I need : ) There has got to be something that I can do to get the right output from this HD alternator - 150A does no good if you can't draw it outta there. It's a Denso 27060-0S020 alternator.

 

Hmm I thought that the cold kit that I have has the 150 amp alt. are you sure yours does?

 

i assume the label looks like this? I havent looked at mine..

 

I was looking at Tundras at Escondido Toyota, pretty sure I saw some with a cold weather package. Double check yours. Either way, not sure how it relates to your problem, since it adds only: Heavy duty battery, heavy duty starter, and deicer grid on windshield. /Mike

 

oh i thought it added HD alt. sorry

 

I don't have the cold weather package, but it does have the heavy duty towing package... which adds the 150A alternator I guess. The label on my alternator shows Denso 27060-0S020, which I couldnt' find much info on. Im wondering if I can introduce a resistor into the sense wire or something to get it to pump up a bit ... or replace the internal regulator all together. If the stock battery isn't supposed to charge at more than 13.8 I'll replace it if need be. Just seems weird that Toyota would change that from the standard 14.4 volts on mosts denso's.

I'm mostly trying to decide if my alternator / voltage regulator is faulty (have you guys verify yours is also low) and I should take it in for service, or if I should just replace the alternator with another one (if even possible).

blackgts2002: do you get 13.8 or less or the standard 14.4 ? Maybe I should put the smaller alternator in : )

 

I wonder if the tow package is only pumping out 13.8 at the trailer connection? That's not going to charge the trailer battery very well.

 

I don't have the cold weather package, but it does have the heavy duty towing package... which adds the 150A alternator I guess. The label on my alternator shows Denso 27060-0S020, which I couldnt' find much info on. Im wondering if I can introduce a resistor into the sense wire or something to get it to pump up a bit ... or replace the internal regulator all together. If the stock battery isn't supposed to charge at more than 13.8 I'll replace it if need be. Just seems weird that Toyota would change that from the standard 14.4 volts on mosts denso's.

I'm mostly trying to decide if my alternator / voltage regulator is faulty (have you guys verify yours is also low) and I should take it in for service, or if I should just replace the alternator with another one (if even possible).

blackgts2002: do you get 13.8 or less or the standard 14.4 ? Maybe I should put the smaller alternator in : )

I will throw a volt meter on it today and let you know later on.
This interests me alot too since I want to add my car audio battery to the rear as well.
-Joe

 

Ive tested voltage at the rear trailor connection, it seems to be about .2 - .5 volts less than at the battery, mainly because of the thin wire they used and the distance. Trailor battery won't charge unless you drive across country.

 

Ive tested voltage at the rear trailor connection, it seems to be about .2 - .5 volts less than at the battery, mainly because of the thin wire they used and the distance. Trailor battery won't charge unless you drive across country.

I double check mine, but looks like I may have to get a small solar panel charger.

 

what about running them in series with a regulator to drop back to 12? can that even be done.. if so would it charge ok?

 

I thought about finding a step up / booster somehow. A 10-14v input relgulated to a 14.4 output - enough to push 20-40 amps for charging. Not sure that it exists though.

I really just wish I had an alternator in this beefy truck that could do what it's supposed to. I was hoping to find some of you testing your output voltage and proving me wrong ...

 

I will today. I did not have a chance to yesterday.

Unfortunatly though, it is performing as it is supposed to in your case. I bet Toyota would give you a lot of slack if you tried to get them to replace.

 

No need to replace if they are all the same. If they can test another Tundra in their service dept that shows the correct voltage I assume I would have no problems having them replace it.

Sam

 

Good point. I will make sure to test that for you.

 

thank you for checking, i appreciate it. If i hear another 1-2 people with the same result I know mine's not broken at least. I assume the max is 13.8, and only if the stock battery needs extra juice - and things are cold. Typically I measure 13.2, sometimes 12.9 even. I could have sworn my battery needle used to sit in the middle at all times ... now its always 1-2 notches to the left it seems. I'm going to fool with the sense wire on the alternator to see if I can give it 1v less to trick it. Bad idea ? I was thinking of running a long 16ga wire to the back batteries for the sense.

 

Yeah, I couldnt find my multimeter. I will keep looking, but my gauge is a little to left of center. center being 14v I think

 

anyone know a product to boost 12v to 14v ? It would have to handle 20-50 amps or so since it would be charging batteries.

 

Well, I just measured mine - '07 CrewMax 5.7L. Started it up in the driveway after about 2 hours since it was last driven and put the meter across the battery terminals:

Got 13.98 volts immediately after starting and as the engine speed came down to idle, it came down to 13.90 volts. I suspect that if I let the engine warm up fully and let idle speed fully drop, I'd probably be at 13.8 volts or less.

You may want to check the voltage output of the alternator with the engine running at your typical cruising speed - I'll bet you get closer to 13.8 volts, or more. I've noted that many Japanese designed alternators seem not to have full output voltage at idle speeds. In my wife's Lancer, you can see the headlights dim ever so slightly and the A/C blower slow ever so slightly when the engine is idling. This may be an emissions thing, but that's pure speculation on my part.

I do know that my Ranger ran about 14.2 volts at idle and that that was within Ford's specs.

It's worth noting that 13.8 volts will charge a battery, just not as fast as if you were to apply 14.0 or more volts. 13.8 volts is the automotive standard for a 12 volt system voltage...

later,
b

 

Here is a link to a voltage booster that may be what you need. Not sure it has enough current capacity, however...

Battour

later,
b