Max amp dc to dc charger for 5.4 owners

[posplayr]

Originally Posted by Kibo

Not sure if it helps any, but my 2011 E350 has the 'EXTRA HVY DUTY 225-AMP ALT' option (from the Monroney) and has had no problem keeping up with my Kisae 50A DC-DC (DMT1250). I do have a new-ish Odyssey 65-PC1750T. I'll have to look the next time I'm charging 50A at idle to see what the battery voltage reads at the Kisae.

I suspect even if you can hold the voltages you will see a noticeable increase in alternator temperature charging that much at idle. Heat is one of the 3 major causes (vibration, electrical stress, and temperature) of electronic failure. You want to keep the temperature out of the RED zone which is about 220+ DegF. Not saying you necessarily have a problem, but rather your alternator temp is going to elevate charging that much at idle (750 APM) vs at say 2500 RPM.

A modern alternator can run at 250 degF but it is significantly reducing its useful life.

My baseline empirical data point on this came from some other SMB member that had a 4WD and was repairing tires on both his and another vehicle's off-road tires. It apparently took about 45 min at idle and it was enough to overheat and effectively kill his alternator. I suspect it was a 130 Amp. He ended up changing out the SCR's in the alternator so the failure was pretty specific to overheating due to an inability to get the heat out.

Another data point is that on a typical day your underhood temperature gets to about 150 DegF (I found a linked somewhere) or more realistically 100 degF (a quoted rule of thumb) above the ambient temp. So for where I live in AZ where it reaches 115 degF that would result in 215 degF under hood temps.

So even a 300 amp alternator is going to have a limited about of thermal mass to absorb that heat and a lot is going to depend on the cooling design of the electronics regulator package on the back of the alternator. So while more is better the 300 amp rating doesn't mean that the alternator can indefinitely change at say 150 amps indefinitely at lower ROM. You would need to look at the temperature and how much you are reducing the useful which gets pretty involved and not a simple thing to determine other than the rules of thumb I have indicated above.

[Kibo]

All good points. I'll see about measuring alternator temperature as well, but of course temps are still pretty cold here in CO so it won't be worst case. We haven't had any issues on trips to Las Vegas, Death Valley, and Texas--so perhaps ignorance is bliss? That said, we don't sit at idle to charge our battery either. Since we have solar, we only start the engine to get on the road to our next adventure.

We also have the Battery Charge Protect wiring hooked up to one of our upfitter switches in case we need it--that might be worth looking into if you think you'll be idling regularly with a heavy electrical load.

[Lcavalletti]

SO while underway today after limiting the 40amp DC to DC charger to 20 amp. I still could not hold a charge on the starter battery of 14.4. I was down to 13. and below consitantly, so I have either already fried the alternator or it simply cannot keep up even at 20 amps with the front and rear air conditioner turned on. .

So I think my next move is to go with a higher amperage alternator.

I can also put a switch on the DC to dc so I am charging only while underway at higher RPMs. ( highway)

id like not to worry about it though and so now I am looking into the 300 amp alternator.

Hopefully this will fix the issue and i think its pretty clear the stock 130amp alternator is not up the task of charging such a large battery.



Next is finshing the kitchen where Ill get rid of the propane SMEG sink burner compo and go with a sink and induction cooktop. propane cooktop no longer needed in the an with a 300AH lithium battery

[posplayr]

FYI, I attached a charging current output vs RPM graph from the manual for 1997 E350 5.4L for 3 different alternators.

You can see the 130 Amp alternator has an 87Amp rating at 2000 RPM.

Interesting there really is not that much effective difference between the 95 and 130 Amp at 2000 RPM (76 vs 87 amps)

The rear A/C fan by itself is about 20 amps on full.

These are probably older performance numbers but give an idea of how current capacity is a strong function of RPM.

[Kibo]

I hadn't even thought of looking it up in the manual (duh!). No pretty graphs in the 2011 manual, but the performance specs are as follows:

• Generator: 70A @ 675rpm (min) to 120A @ 2,000rpm (max)
• Generator (Extra Heavy-Duty Option): 90A @ 675rpm (min) to 155A @ 2,000rpm (max)
• Generator (Super Heavy-Duty Option): 135A @ 600rpm (min) to 225A @ 2,000rpm (max)

Note that the first two have a pulley ratio of 2.72:1, but the 225A alternator uses a 3.00:1 pulley.

So it would seem that the 225A alternator outputs roughly 2x as much current at idle as the standard (120A) alternator, more than the max capability of the standard alternator.

[posplayr]

Originally Posted by Scalf77

My assumption is that he is seeing the lower voltages when the alternator is closer to idle. It really depends on what additional electrical loads one is running at the time this is happening. Remember the The surepower and B/S ACR would monitor voltage, if the voltage dropped below 12.8 volts the units would disconnect, thus reducing any load coming from the "house system".

-greg

As mentioned by greg, there can be a smart relay in the mix as well for an SMB

This is something I keep forgetting about because I don't have a "Surepower or equivalent "smart relay". If this is in series with the DC-DC then it is an integral part of the shutdown (low Chassis charging) behavior.

What worries me about the DC_DC behavior of the renogy for sure and others that are alike is that they boost voltage all the way down to like 8V (see spec sheet attached). What exactly happens between the DC to DC trying to extract more power from the alternator/battery package that is available is kind of complex.

If the alternator current maxes out, the output voltage probably drops to the battery terminal voltage and then you are just pulling current from the battery in excess of what the alternator can provide. In this case, the ACR would stop any such nonsense from occurring.

Since I don't have an ACR I would want to manage the charging control manually. Alternatively, I have looked at automatic thermal shutdown or even more elaborately a managed thermal control (using a microcontroller).
The simple way to do this is in the figure attached which uses an inexpensive thermal switch.

The idea is that The red rocker switch lights RED when with 40A (UP) or 20A (DWN) off-center positions (used to control D+ and LC on the renogy). The voltmeter can be seen from the driver's seat and monitors the HAUS battery voltage.

The relay is there to cut out the controls and turn off the DC-DC completely if the thermal switch closes. I was looking at the 80 degC rated switch but these are not that precise and have a pretty wide range so that may need some adjustment.

My plan was to just take a strip of brass/copper and wrap it around the temp switch and drill a hole (in the strip) and use a mounting screw on the back of the alternator. One wire would be grounded at the alternator case mount and then a single switched ground wire would be run to the cockpit where the relay and switches are.

While optional, I added another RED warning light to indicate the DC-DC was shut off in an over temp mode.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Anyhow food for thought for how to best control the DC to DC . There is a thread somewhere on an RV forum that describes various ways to control the renogy 40A DC-DC using voltage control with an off-the-shelf controller board. Ultimately my conclusion is that this is all indirect control and you still need some type of thermal control coupled with some sort of voltage which is why I also started developing a microcontroller solution with a display.

[posplayr]

FYI here is some of the info I found before on Engine bay temperatures.



https://www.z06vette.com/threads/wha...-reach.113545/


http://www.cleanmpg.com/community/in...?threads/3471/

[Scalf77]

A couple of things when trying to pick a DC-to-DC converter. When choosing a size, it will be a question of the size of your battery bank, all the additional loads on the system (and what battery system they are attached to, house or van?), and the capability of the alternator. While the size of the house battery bank would have a big impact on current demand The result with a DC-to-DC converter is different, the load will be dictated mostly by DC-to-DC converter, not by how much the DOD of the battery is. So, the max bulk rate charge for the battery will be dependent on size of the output of DC-to-DC converter. In the case of the OP the size was 40 amps. It would be 40 amps with a 300 Ah battery bank, or a 100 Ah battery bank. The absorption phase will be a correlation to the battery bank size. In the case of a lithium battery bank, the absorption phase will be short.

Your battery bank size will be important when choosing the size of the DC-to-DC charger you want. If your 300 Ah battery is discharged 100Ah than it would take 2 and ½ hours with a 40-amp charger versus the 20-amp charger would take 5 hours (this doesn’t consider, the absorption phase)
The load the DC-to-DC converter presents to the alternator will be driven by the voltage and current level of the settings. You will need more power on the input side due to conversion loss. You will need more current on the input to the alternator than the output of the converter. All the other electrical consumers on the starting battery side will also come from the alternator, lights, air conditioning or heater (blower), stereo.

Now here is where the DC-to-DC differs from the traditional ACR approach, where the two systems were put in parallel. Now any loads that were before coming off the house system while driving will be getting their power from the house system. This means if you have a 5-amp load, it will be coming out of the 40-amp output of the DC-to-DC unit. This was a fairly big impact when running my Starcool system, it derived it’s 12-volt power from the house battery system. A blower on high would consume a lot of power that was supposed to be going to the house battery recharge. So, it is important to understand where the loads are connected.

The other side of the equation is the alternator not keeping up with load demand on the system. The alternator is usually just a simple voltage regulated output. If the voltage output is to low the alternator will provide more power so that voltage will go back up. Of course, at some point it won’t be able to provide more power and the alternator won’t be keeping the voltage up. As seen from data in this thread the power output at idle is much lower than the rated output of the alternator. If it can’t keep up with the load, the big effect will possibly damage to the alternator, and not charge the starting battery. This will create additional loads on the system as the starting battery load will get larger the more discharged the battery is.

Unfortunately, the OP probably purchased the one of the worse DC-to-DC converters available. At least in the area of protection and features. Many DC-to-DC converters monitor the input voltage much like an ACR. If the voltage drops the units will turn off. This is a feature of the KISAE DMT1250 that @Kibo referenced. It also takes a check every three minutes to monitor things and measure voltages. It can also throttle itself down to a lower output. This is also a feature of Victron DC-to-DC converters.

If you are concerned with alternator temperature Sterling power has models that support an additional alternator temperature probe. Note: Sterling power units are identified by their input current. This is probably better for planning purposes, but different then how most the other units are sold.

-greg

[Kibo]

Originally Posted by posplayr

FYI here is some of the info I found before on Engine bay temperatures.

Not to be a naysayer, but I'd be cautious about drawing direct conclusions based on data from other vehicles. A 'vette or Insight have vastly different (much smaller) frontal cooling area than an E-series. So look at the trends, but to really draw conclusions you'd have to instrument up a van and do your own testing.

[posplayr]

Originally Posted by Kibo

Not to be a naysayer, but I'd be cautious about drawing direct conclusions based on data from other vehicles. A 'vette or Insight have vastly different (much smaller) frontal cooling area than an E-series. So look at the trends, but to really draw conclusions you'd have to instrument up a van and do your own testing.

I agree as it is clear that there are many variables but ambient temp is probably going to dominate.

Automotive temp ranges typically go to +125C which is 257F. Again a rule of thumb for under hood temps would be Tunderhood ~ ambient +100 F


https://en.m.wikipedia.org/wiki/Operating_temperature