New alternator. DC to DC breaker issue.

[dbhost]

So I had a new alternator installed. 93 E250 Sportsmobile. Replaced the 120amp alternator with a 150.

The DC to DC charger is protected via a Red Wolf 60 amp marine breaker.
https://amzn.to/3YlFX2k

Problem is, with the new alternator installed, after about 10 minutes the breaker throws. I am watching the BMS at least, what is being pulled by the battery and running appliances is ~30 amps. NEVER above 35 amps,

I have seen some reviews on these breakers that says they go bad pretty fast, I am just wondering through, is there a way to tell if the breaker is bad, or if perhaps the alternator is throwing too much at it?

 

[kbeefy]

The alternator won't 'push' more amperage than the dc-dc asks for. It's indirectly (or directly) connected to your starting battery, so it can get as much amperage as it wants anyways, regardless of what your alternator puts out.


I'd replace that CB with a quality one.

 

[dbhost]

... I'd replace that CB with a quality one.

Not sure what a quality marine circuit breaker would be... Too many options. Definately need soemthing inline.

 

[kbeefy]

A blue sea version of what you have.

 

[boywonder]

That Red Wolf breaker appears to be an Asian knockoff of a Buss/Bussman.


Buy the real thing...


https://www.amazon.com/Bussmann-CB2...ve&sprefix=bussmann+60a,automotive,174&sr=1-1


I'm sure a Blue Sea breaker would be a quality component as well....

 

[kbeefy]

I assume Buss makes the Blue Sea one, I couldn't remember the brand.

 

[posplayr]

Problem is, with the new alternator installed, after about 10 minutes the breaker throws. I am watching the BMS at least, what is being pulled by the battery and running appliances is ~30 amps. NEVER above 35 amps,

So, that knockoff resettable fuse may be marginal, but resetting at 1/2 the rated current doesn't sound right. I would suspect that there is more current going into the DC to DC than you think, probably more than the rated 60 amps.

I'm only going to go into enough detail so that you understand the potential issue. The typical DC-DC converter can operate down to 8-10 volts, and (since you have a BMS) I assume you are charging a lithium battery. That means that if you don't have adequate cabling between your alternator and the DC to DC, then the DC-DC can pull substantially more than the current that is being delivered to the BMS.

I don't know your details but the alternator draw can be in the range of 30%-50% more than the battery charging current. So I would get a current clamp amp meter and measure what is going through that fuse and into the DC-DC.

Several questions I would have is :

• Did you update the cabling to the alternator?
• Where or how are you connected to the battery/alternator?
• What size cabling did you use and how long is it?
• Have you calculated the expected voltage drops?

The first step before going down this rabbit hole is to measure you currents.

You need a DC current clamp; here are several based on your budget.

https://www.amazon.com/Best-Sellers-Clamp-Meters/zgbs/industrial/5011680011

 

[Scalf77]

The stated data of 30 -35 amps going into the battery (measured by BMS) would be somewhat misleading. You also reverence having running some appliances. I believe if I remember one of your other post you installed a no-name DC-to-DC charge (40 amp). If we assume that is referencing a 40 amp output, (usually true, but not always) then we would have expectations that the DC-to-DC charge was putting out close to 40 amps ( depending on what phase the charger is in) If we take that and subtract any of the appliances and always on things that are running, we would get the measurement of what is going into the battery or being measured via the BMS. They key here is the load that is presented to the alternator is from the 40 amp DC-to-DC charger. What is connected on other side of the charger for the most part is irrelevant.

Of course the DC-to-DC conversion does not come for free, so if we take 80 - 90% efficiency we would get around 45 - 53 amps. This value can be impacted by environmental factors, wire size, output voltage of alternator, etc.

 

[boywonder]

So I would get a current clamp amp meter and measure what is going through that fuse and into the DC-DC.

^^^^^^^ That will answer all of the questions posed.....in seconds.

 

[posplayr]

Of course the DC-to-DC conversion does not come for free, so if we take 80 - 90% efficiency we would get around 45 - 53 amps. This value can be impacted by environmental factors, wire size, output voltage of alternator, etc.

I cant find my spreadsheet now, and I was doing these calculations close to 3 years ago but as I recall using a 3% voltage drop rule I was getting close to 55-60 amps draw from the alternator to deliver 40 amsop at the output of the DC-DC.

For example, if you need 14 VDC for your particular batteries, and you are only delivering 11 VDC to the input (because of underrated cables over too long of length)of the DC to DC, then you need an additional amount of input current. The total would be 40*14/11=50 amps.

If OP's new alternator was installed without upgrading his grounds and he connected to the battery then it might be worse.

Assuming Scalf77's mid range DC to DC efficiency numbers of 85%

Then you are looking at 40*14/11*1/0.85= 59.8 Amp (to the DC-DC) in order to deliver 40 amps out of the DC-DC.

In my judgment, this is why the stock alternators will burn up at idle, much more current than one would think.

 

[Scalf77]

I would assume that the DC-to-DC has a low voltage disconnect setting. I would suspect it to be around 12.8 volts.

 

[posplayr]

I would assume that the DC-to-DC has a low voltage disconnect setting. I would suspect it to be around 12.8 volts.

The Renogy 40A dc-Dc doesn't and as far as I recall I have never seen one mentioned on any dc- dc . The BMS has one but that can cause a load dump. They all seem to be very proud that they will boost down to 8.5v input to charge at 14v

 

[dbhost]

Several questions I would have is :

• Did you update the cabling to the alternator? Yes. I ordered the alternator and cabling as a matched pair from Summit Racing as they had the high output alternator. There is literally no size difference in cables though...
• Where or how are you connected to the battery/alternator? The cable runs from the chassis battery to where the battery isolator originally was, breaker is installed here...
• What size cabling did you use and how long is it? I reused Sportsmobiles cabling which I believe is 4ga. It runs from the engine compartment, along the frame to the electrical compartment next to the drivers side wheel well...
• Have you calculated the expected voltage drops? No. I mostly reused Sportsmobile's existing cabling.It was outfitted with a 45 amp converter / charger, and I have no clue what capacity the OE battery isolator that has been since bypassed was.

Prior to the alternator replacement the system was in place and working well. The relevant things that changed are the alternator, and the signal wire got moved from the the fuse box to the signal wire on the alternator itself.

The DC to DC charger / MPPT charge controller is an AtemPower unit. They are a reasonably known brand but not as well situated in the market as Renogy or Victron... And yes it is a relabelled Chinese unit I am sure...

 

[Scalf77]

Assuming you haven't tied the ACC line to the ignition, then your unit would stop when falling below 12.5 volts. It starts charging when the voltage is 13.0 and above.

I would suspect that the new alternator has a slightly lower voltage output than the older one.

 

[dbhost]

I would suspect that the new alternator has a slightly lower voltage output than the older one.

That is easy enough to test...

 

[dbhost]

Okay the signal wire might still be a problem...

There is the obvious charging cable that comes off the alternator, but there is also the hot / run signal wire that feeds the voltometer on the dash. The signal wire was supposed to tap into that... I have electrical tape and nothing better to do. I am going to try running without that signal wire as it is marked as "optional"...

 

[Scalf77]

The "signal wire" as you call it is to tell the DC-to-DC that you are running a "Smart" Alternator via the ACC connection. You are not, so you do not want that connected.

 

[posplayr]

Okay the signal wire might still be a problem...

There is the obvious charging cable that comes off the alternator, but there is also the hot / run signal wire that feeds the voltometer on the dash. The signal wire was supposed to tap into that... I have electrical tape and nothing better to do. I am going to try running without that signal wire as it is marked as "optional"...

Out of curiosity where is the 60 amp (that blows) fuse located?

 

[dbhost]

Out of curiosity where is the 60 amp (that blows) fuse located?

On the lead from the chassis battery to the charger...

 

[Scalf77]

The ACC connection is not really explained well on a lot of Dc-to-DC chargers. Your first thought is that I would attach the ACC input to the Alternator D+ terminal or to some circuit that is hot while the engine is running. AKA the alternator should be charging.

The reality is the input of the DC-to-DC charger is much like a Blue Sea ACR. It monitors the voltage, and if the voltage is high enough it turns the charger on, if it falls below a certain voltage it turn the unit off. These voltages are usually in line with what you see when the engine is on or off.

In the case of your ATEM unit the turn on voltage is 13 volts (no ACC) and the disconnect voltage is 12.5 volts (no ACC). IMO the 12.5 settings is to low, but a separate discussion.


Now if you were running a vehicle with a Smart Alternator the voltage output is much different. So for that vehicle we would set up the ACC input to the D+ signal or Engine Running Hot circuit. This would change the DC-to-DC charge to start charging at 12.5 volts and turn off at 10.8 volts This would be more inline with the output voltages of a smart alternator.

Now back to the blown circuit breaker. Sound like you were hooking up the ACC circuit, but did it at the alternator with the new unit and were previously hooked to a different fused location. If the previous fused connection was not correct or working as you expected this could somewhat explain the issue.

With the new alternator hookup, if the ACC hooked up to the D+ signal, you would have the capability to run at the lower voltage setting and putting you closer to the ratings of the breaker.

Even with that hooked up that way, the load you presented to the alternator would have to be to much for the alternator to keep up with. You went with a larger alternator, so we would think you have more available power, but one would need to look at the power curve to be sure. The important variable is what the output is a idle.

I would get the vehicle in idle (normal) and measure the voltage. I would then turn on the ATEM and measure the voltage, as we increase the load the voltage will go down and the alternator will produce more power to bring the voltage back up. After that you would turn on headlights, air conditioner, heater, or any other consumers that are getting power from the start battery.
Ultimately you hope the Alternator can keep up with the consumption at idle. If not, and the voltage drops below 12.5 (No ACC) the ATEM would disconnect and save your alternator and van electrical