undercharged relocated battery w/alternator

[RSB]

greetings gentlemen. I'm having some trouble w/my dual battery setup and I'm hoping someone might be able confirm my line of thinking on this...

although my house battery will recharge at a minimum of 13.9 volts, it requires between 14.1-15 volts to charge sufficiently w/an alternator. With my vehicle in motion and alternator running, I'm only reading between 13.65-14.1 volts connected to 12 ft of 0/1 wire. This is likely due to cable loss, as my alternator should be putting-out 14.5-15 volts.

the battery is recharging, however, the rate of charge clearly isn't adequate to recover the battery when heavily discharged. I'm thinking I need a bigger alternator to solve this problem. Sounds like a simple fix, but I want to be sure before pulling the trigger.

thanks in advance for your input.

 

[iigs]

I'm only reading between 13.65-14.1 volts connected to 12 ft of 0/1 wire. This is likely due to cable loss, as my alternator should be putting-out 14.5-15 volts.

I suspect that's not the case. It would take approximately 175A of draw to drop half a volt on that cable. I don't believe a regular lead acid battery would draw that kind of current, and even if it did, I don't believe it would for very long -- as the voltage of the alternator and the battery converge current demand will drop.

More than 14.4v seems like a lot for a normal passenger car alternator. Can you check it on the output terminal of the alternator? That will factor out voltage drop. A lot of batteries charge fully at 13-13.8v; I would view that as an acceptable output voltage for a normal OEM alternator (net 13.8v on the output post, after all regulators, etc).

Does the voltage sag at idle and rise as RPMs go up? If so, you might be able to change the pulley on the alternator to raise the idle speed. If that's not desirable for whatever reason, you may wish to find a good quality lower amperage alternator. Somewhere online I once saw a graph of two models of alternator from the same manufacturer -- one high amperage and one low amperage. The high amp model put out more amps, as advertised, but the power dropoff point was at a higher RPM. The lower amperage alternator could sustain its rated amperage at a far slower speed.

Edit: after rereading your post, I disagree with your diagnosis of voltage drop but think your course of action is correct. I suspect you'll not see much drop (which is good -- if you do, you definitely should fix that first: more cable) It sounds like your battery is unusual and would respond well to one of the special "hot" car audio alternators that has a higher output voltage.

 

[tremors834]

Ryan,
Going on some "industry standards" at 80 degrees -
100% charged battery = 12.68 volts
50% charged battery = 12.24 volts


A alternator that is operating correctly should at idle put out 13.5-14.4 volts. If it's putting out less than 13.5 volts then the alternator is no good, although even that is open for debate without amperage draw readings.

The voltages you've given fall right in line.
Have you actually experienced a slow rate of charging or is it speculation?

If you experienced it, what type of load is on the system (aux. lighting, radio gear, etc) when the battery becomes heavily discharged?

How new is your dual battery set up?

What type of, if any, of isolation between the house and aux battery are you using (relay/solenoid, electronic/diode isolator, heavy duty mechanical switch)? Diode Isolators are notorious for having up to a 1.5 volt volatage drop across it

How old and have the batteries been load tested? A bad battery will keep a constant amperage draw on an alternator causing a low alternator output voltage, but the battery may still read like its fully charged at 12.6 volts with no load on the battery.

 

[RSB]

Ryan,
Going on some "industry standards" at 80 degrees -
100% charged battery = 12.68 volts
50% charged battery = 12.24 volts

my battery is an Odyssey PC1700MJT. I've been going back & forth discussing this w/Odyssey engineers and they say the battery is fully charged at 12.83 volts, and recommended alternator output is between 14.1-15 volts. Compare that to my Optima at 13.65-15...

I figured I could rule-out cable loss if I tried connecting the alternator directly to the battery with only 3 ft of cable instead of 12. Surprisingly, I'm still getting the same voltage with the truck in motion, around 13.5-13.8 volts. Therefore, cable loss is a non-issue. And, that's within the range you're saying of correct operation. However, my concern is that even w/the truck in motion at 13.65-14.1, by Odyssey's standards, it still isn't enough to charge the battery sufficiently after being heavily discharged. Also, Toyota said I should expect the alternator to push anywhere between 14.5-15.

A alternator that is operating correctly should at idle put out 13.5-14.4 volts. If it's putting out less than 13.5 volts then the alternator is no good, although even that is open for debate without amperage draw readings.

The voltages you've given fall right in line.

honestly, I probably haven't discharged the battery enough to know for sure. I'm going to try this tonight. What sparked my concern was with my battery monitor and it not showing it fully charged, despite programing it with the correct variables. This is when I figured-out the voltage didn't correlate with what Odyssey said I should be reading on my voltmeter, which can explain why my monitor isn't indicating the battery being fully charged. To further support my suspicions of having a low rate of charge, driving the truck around for an hour beginning at 12.6 volts, I still haven't got either battery to 100% capacity (the Odyssey at 13.18 and the Optima at 12.83).

Have you actually experienced a slow rate of charging or is it speculation?

I tried w/running my aux lights and air compressor for awhile, but probably not long enough. I'm going to try again tonight with a loaded winch and then observe how long it takes to recharge.

If you experienced it, what type of load is on the system (aux. lighting, radio gear, etc) when the battery becomes heavily discharged?

brand-new. Xantrex Pathmaker 250 amp batt combiner, Odyssey PC1700MJT and Optima 34/78.

How new is your dual battery set up?

solenoid that connects the house batt w/the starter when voltage exceeds 13.1 volts.

What type of, if any, of isolation between the house and aux battery are you using (relay/solenoid, electronic/diode isolator, heavy duty mechanical switch)? Diode Isolators are notorious for having up to a 1.5 volt volatage drop across it

batteries are brand new. I'm not sure how to do a load test, how is that done exactly? I might have. Can a bad battery be determined by reading the voltage directly off the alternator and comparing it to the voltage off the battery?

How old and have the batteries been load tested? A bad battery will keep a constant amperage draw on an alternator causing a low alternator output voltage, but the battery may still read like its fully charged at 12.6 volts with no load on the battery.

thanks for the help!

 

[RSB]

yep, I connected the alternator directly to the battery with only 3 ft of cable instead of 12 and got a reading about the same with the truck in motion, around 13.5-13.8 volts. Looks like cable loss is likely a non-issue.

I suspect that's not the case. It would take approximately 175A of draw to drop half a volt on that cable. I don't believe a regular lead acid battery would draw that kind of current, and even if it did, I don't believe it would for very long -- as the voltage of the alternator and the battery converge current demand will drop.

good idea. I'm going to try this tonight.

More than 14.4v seems like a lot for a normal passenger car alternator. Can you check it on the output terminal of the alternator? That will factor out voltage drop. A lot of batteries charge fully at 13-13.8v; I would view that as an acceptable output voltage for a normal OEM alternator (net 13.8v on the output post, after all regulators, etc).

yes. However, even at high RPMs, the voltage still isn't within Odyssey's standards for what they consider a sustainable rate of charge.

Interesting! I didn't know that about the alternators. If it's an alternator I need, I will definitely take that into consideration. Thanks!

Does the voltage sag at idle and rise as RPMs go up? If so, you might be able to change the pulley on the alternator to raise the idle speed. If that's not desirable for whatever reason, you may wish to find a good quality lower amperage alternator. Somewhere online I once saw a graph of two models of alternator from the same manufacturer -- one high amperage and one low amperage. The high amp model put out more amps, as advertised, but the power dropoff point was at a higher RPM. The lower amperage alternator could sustain its rated amperage at a far slower speed.

thank-you!

 

[RSB]

so, next I'll try testing the alternator directly to see what voltage is actually being pushed-out. If it's not within Odyssey's requirements of 14.1-15 volts, this is my problem.

 

[RSB]

ok, so looks like I'm getting 13.78 volts off the alternator. I called a different Toyota service center and was told the alternator should be pushing 12.2-13.8 volts, not the 14.5 I was told earlier.

therefore, my alternator is working normally and supplying sufficient voltage, even with 12 ft of additional wire. However, by Oddyssey's standards, the voltage is still inadequate.

I'm going to conduct some high load tests for further testing, however, I suspect I might need to upgrade the alternator to get the higher rate of charge the Oddyssey is looking for.

 

[HenryJ]

Perhaps just a change of regulator if the alternator that you have is adequately sized. If you have the option , connecting the remote sensing wire to the desired measurement location can help. That way the alternator trys to maintain the set voltage at that point rather than internally.

 

[RSB]

thanks! I thought about that but Toyota said the regulator can't be adjusted. Perhaps there's a way to modify this by adding an external regulator, assuming the alternator is adequately sized, like you said. I'll look into this.

Perhaps just a change of regulator if the alternator that you have is adequately sized. If you have the option , connecting the remote sensing wire to the desired measurement location can help. That way the alternator trys to maintain the set voltage at that point rather than internally.

 

[UglyScout]

I'd be more worried about an alternator putting out close to 15 volts than one putting out closer to 14 volts. To me it seems your system is working perfectly. You'd hate to monkey with the factory regulator, kick up the volts and fry the trucks computer...

I'm sure in an ideal world Odyessy would want more volts to 'fully' charge but if you haven't drained the battery a sufficent amount the alternator isn't seeing the demand.

 

[RSB]

here's an email reply I received from one of Odyssey's engineers regarding voltage output from the alternator...

At 13.65 the voltage is very low. The recommended min-max voltage at the battery from the alternator is between 14.1V to 15.0V. Voltages greater than 15.0V will overcharge the battery and cause premature failure. At voltages less than 14.1 you run the risk of never getting the battery fully charged. Consistent undercharging which caused sulfation is the leading non-warranty cause of premature failure of the ODYSSEY battery. If the application is in a vehicle that has infrequent stops and is truly used only for starting then 13.6V would be the minimum acceptable voltage at the terminals however if the batteries are being cycled or the vehicle has frequent stops, then fully charging the battery (which prevents and reverses sulfation) will be nearly impossible.

 

[RSB]

I was thinking the same thing! If 13.85 (max alternator output) is good enough (given the demand) to charge at the minimum of 13.6 volts, then I should be alright. I need to conduct some high load tests...

I'd be more worried about an alternator putting out close to 15 volts than one putting out closer to 14 volts. To me it seems your system is working perfectly. You'd hate to monkey with the factory regulator, kick up the volts and fry the trucks computer...

I'm sure in an ideal world Odyessy would want more volts to 'fully' charge but if you haven't drained the battery a sufficent amount the alternator isn't seeing the demand.

 

[RSB]

I'm sure in an ideal world Odyessy would want more volts to 'fully' charge...

this sounds to be the case. Here was my previous reply:

Kathy, guess I do have one more question!

you mentioned 14.4 - 14.8 volts for where the alternator needs to be. Does this mean 14.4 volts is the minimum voltage needed for the batt to charge? I was told by a rep yesterday the minimum voltage to charge w/an alternator was 13.9 volts.

first, I was told 13.9. Then it was 14.4 (min alternator range), and now 13.6! 13.6 is within the range of my stock alternator, between 12.2 and 13.8 volts.

 

[RSB]

ok, so I performed some high load tests and managed to get the aux battery down to under 11 volts. When the engine starts, the batteries connect together when voltage from the starter batt exceeds 13.1 volts. When this happens, the aux battery immediately draws around 30 amps to start recharging. This brings down the voltage on the starter battery to around 12.2 volts. The batt combiner disconnects at anything below 12.8 volts (the lowest setting). Therefore, the batteries are disconnected a few seconds later.

this tells me the alternator doesn't appear to be supplying enough voltage to keep the solenoid connected and consequently, prevents the aux battery from re-charging (when discharged to this capacity). I didn't expect to figure this out before even getting a chance to observe the rate of re-charge! I guess a new high output alternator is needed after all.

 

[wrcsixeight]

The alternator in a vehicle is not designed to fully charge a battery, compared to the charging system in a blue water sail boat, which might have 3 stage charging with battery and alternator temperature sensors and compensation algorithms. You can do what you can to help it out, with thicker, shorter charge wire but if the thicker wire is only between the isolator solenoid and second battery, and you are relying on the OEM wiring between alternator and engine battery, then 4/0 gauge will do nothing extra when wired between the isolator and second battery.

If you do not add thicker ground wires as well, then you will not increase the amps or current. Put a thick ground wire from alternator to the engine/ frame. Between battery and engine and frame, frame and engine. Give it multiple paths.

My Dodge Van has a 130 amp externally regulated alternator. I have seriously upgraded the charging circuit. I have 1 engine battery and 2 flooded true deep cycle house batteries 115 a/h each. I also have solar and a battery monitor which reads alternator amperage, and this tool has been a big eye opener.

My Voltage regulator is internal to the engine computer, but luckily it only throttles back the output after the batteries reach full charge, or once ~14.5 volts is met. The only other times the voltage is lower than 14.5, is at low rpm, with depleted batteries. Once it reaches 14.5 volts, the alternator only puts out enough amperage to hold that 14.5 volts. Unfortunately that amp number can be 15 amps despite my batteries being over 70 amps from full. So If I were to rely on the alternator to fully charge the batteries, I'm looking at close to 5 hours.

Even though my batteries could easily accept 40 amps, the alternator only needs to produce 15 to 20 amps, if that, to hold the 14.5 volts, so that is all it does. So my 130 amp alterantor is gonna need 5 hours of engine speeds above 1800 rpm to replace 70 amp hours into my batteries. It sucks, but that's the way it is, on my vehicle, on yours, and nearly every one out there.

I also suffer from despicable amperage at idle speeds when the alternator is hot. It simply cannot make more than 32 amps at idle speed when hot. If I have my high beams on, and blower motor on high, 10 amps are flowing from my batteries. The alternator simply cannot make the amperage at low rpm to make enough current to keep the batteries up in the 14's. You cannot add more load to the alternator and expect it to charge your batteries any faster.

Since your Toyota's voltage regulator was designed to never go above 14, as soon as it sees 14 volts, it only allows the alternator to make enough current to keep this voltage, this your battery is never gonna fully charge via the alternator in any hour long drive. Not gonna happen.

Even if You got an alternator that is designed to make big amps at low rpm's, the limiting factor is the voltage regulator. Once that voltage setpoint is reached, it cuts the alternator down.

Basically you have few options Your 13.8 volts is the limiting factor.

You can add a voltage dropping Diode in the alternator sense wire, so the voltage regulator sees a lower voltage and allows the alternator to put out more amps at higher volts, but this only works with externally regulated alternators.

You can try adding a separately regulated alternator, but with a shared ground, things can get a little complicated.

You can try keeping the battery and alternator cooler. Most all computerized vehicles try to regulate battery charging voltages by temperature. The higher the temperature,the lower the charging voltage. It might have a battery temp sensor, or it might just guess using the coolant temp sensor or an ambient air temp sensor and a programmed algorithm.

Basically, whenever you deplete your batteries, when you get home, you need to top them off by plugging a charger into the grid. That helps keeps the batteries healthy, and reduced stress on your charging system.

My engine idles so much smoother when the alternator only has to add 2 amps into the batteries, instead of 32. It takes 1 HP for the alternator to produce 25 amps. It is not free electricity.

Here is a link to a chart showing how much better a 120 degree alternator performs than a 190 degree alternator.

http://www.betamarinewest.com/balmar/6-series-sheet-web.pdf
You can also see how some of the lower amp alternators produce more amps at lower rpms than the higher amp alternators. Keep in mind, these are the Balmar alternators, pretty much the top dog in the blue water sailboat world, where they need to reliably recharge a large bank of batteries as quickly as possible at lower rpms. They perform way better than a vehicle alternator/ charging system that was designed to top off a small, single, slightly depleted starting battery.