New alternator. DC to DC breaker issue.

[dbhosttexas]

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.

[dbhosttexas]

Originally Posted by kbeefy

... 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-CB28...e%2C174&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]

Originally Posted by dbhosttexas

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-...ial/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]

Originally Posted by posplayr

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]

Originally Posted by Scalf77

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.