Rookie alternator questions

[GallenH]

Frequent discussions about 2nd alternator prompt me to ask:

Can you circumvent a 2nd alternator by replacing your current alternator with a higher output unit? What adjustments (wire guage) would have to be made?

If you have a 2nd alternator dedicated to house batteries, would you need an isolator or would you just have one drive the house batteries and the existing drive the chassis battery?

Thx.glenn

[GallenH]

Forgot an additional consideration: If your house batteries were being charged from the alternator with a b2b charger post alternator would you even need an isolator or would the b2b prevent the depletion of the chassis battery?

[avanti]

The primary issue that has driven the adoption of 2nd alternators has to do with the increasing use of "smart" managed electrical systems on modern vans. Vehicle alternators are not what they used to be. Rather than conventional regulators, they are LINbus controlled, so the ECU has direct control over output. This permits the implementation of algorithms that save fuel in various ways. For example, starter batteries are intentionally under-charged, leaving room to harvest energy when coasting down hill. Also, charging is suspended briefly during acceleration in order to off-load the engine. The battery has a shunt and other sensors mounted on it to optimize charging. The ECU will notice if you turn on a high-current load and compensate accordingly. These and other techniques make power takeoff a dicey proposition, even if you have plenty of alternator capacity.

There are B2B chargers that have features to compensate for this, but far better to leave the highly-engineered vehicle electrical system to its own devices and keep the house system completely isolated from the chassis. THAT is exactly what a second alternator accomplishes. It allows there to be zero cross-connection between house and chassis.

They are usually controlled via special regulator/chargers such as the Balmar products, so you can tune the charging profile to your particular house battery.

This all adds up to a far superior system to any one that attempts to steal power from the chassis.

The Transit has a dual alternator option that is specifically designed to provide lots of power to external loads such as a coach. That is a slightly different story.

[booster]

I think Gallen has an older Dodge Pleasure-way Excel, so he would likely not have any of the modern alternator controls except maybe having the voltage regulator in the PCM (not sure on the Dodges when they changed from standalone alternators).


On a system that isn't as tied in you have more options like going to a larger alternator or adding a second one either as a standalone with it's own regulator or even in parallel with the first alternator which is what we did as it reduces the load and heat issues the single ones can have on large battery banks with high acceptance. Both alternators can then be put on a remote regulator to get good charge control.


There are upsides and downsides to all of the options, so it is generally necessary to look carefully at what is needed for more charging and the existing system to figure out what is the best way to go with it.

[avanti]

Originally Posted by booster

I think Gallen has an older Dodge Pleasure-way Excel, so he would likely not have any of the modern alternator controls except maybe having the voltage regulator in the PCM (not sure on the Dodges when they changed from standalone alternators).

Ah. Sorry. I didn't realize we were talking about retrofits.

[booster]

Originally Posted by avanti

Ah. Sorry. I didn't realize we were talking about retrofits.

Good point, we may or may not be in this case as not completely clear. I assumed we were.

[markopolo]

Originally Posted by GallenH

Forgot an additional consideration: If your house batteries were being charged from the alternator with a b2b charger post alternator would you even need an isolator or would the b2b prevent the depletion of the chassis battery?

You don't need or want a typical diode type Isolator if using a DC-DC (B2B) charge controller (charger).

If the DC-DC (B2B) charge controller is ignition switched then the chassis battery should be OK. Boost/buck DC-DC (B2B) charge controllers can pull the chassis battery voltage down if the alternator can't supply all the power needed by the DC-DC (B2B) charge controller. An example would be a hot alternator with van idling in traffic with air conditioning on or engine cooling fans coming on etc. Voltage triggers controlling the DC-DC charge controller can eliminate that.

Generally, uni-bidirectional vs bidirectional charge control is as follows:

Chassis side to House battery uni-directional charging
- Isolator
- ignition switched DC-DC charge controller
- ignition switched Solenoid or relay
- second alternator (not in parallel) dedicated to House battery side.

Chassis and House battery bidirectional charging
- ACR
- some Separators
- manually switched Solenoid or relay

[GallenH]

Sorry to have not included info about my old age......er.....the van's old age. My PW has the largest alternator that they put on the Dodge van/wagon: 136A. I am considering upping the 100AH house battery I have to 200AH and don't want to stress out the existing alternator. But I was also wondering about the isolator/separator. Would replacing that with a B2B add good regulation of the charge to the house batteries and also, since it seems to be a one-way flow device, prevent the depletion of the chassis battery from house draw? If so, would a separator/isolator be needed?

[GeorgeRa]

Originally Posted by markopolo

You don't need or want a typical diode type Isolator if using a DC-DC (B2B) charge controller (charger).

If the DC-DC (B2B) charge controller is ignition switched then the chassis battery should be OK. Boost/buck DC-DC (B2B) charge controllers can pull the chassis battery voltage down if the alternator can't supply all the power needed by the DC-DC (B2B) charge controller. An example would be a hot alternator with van idling in traffic with air conditioning on or engine cooling fans coming on etc. Voltage triggers controlling the DC-DC charge controller can eliminate that.

Generally, uni-bidirectional vs bidirectional charge control is as follows:

Chassis side to House battery uni-directional charging
- Isolator
- ignition switched DC-DC charge controller
- ignition switched Solenoid or relay
- second alternator (not in parallel) dedicated to House battery side.

Chassis and House battery bidirectional charging
- ACR
- some Separators
- manually switched Solenoid or relay

I use Magnum ME-SBC Smart Battery Combiner wired in the way allowing me to control charge direction to house batteries to engine battery or reverse. The unit limits max charge to 25A.

I was considering KISAE DMT1230 B>B charger but already had ME-SBC and wouldn’t be able to charge engine battery, and I use this function often to keep engine battery topped.

Doing it today I would replace my Mornigstar Solar Charge controller and ME-SBC with a two sources capable B>B such as KISAE and an engine battery maintainer.

[markopolo]

Both devices are interesting. The current limiting of the Magnum ME-SBC seems to be PCB or FET temperature driven causing either a full interrupt or a reduced duty cycle. I'm not 100% certain of that though but that's all I could gather from the manual. No boost/buck so it's dependent on the capability of a separate charging device if one wants to meet specific charging criteria.

A Kisae DC-DC + something like a Trik-L (PbA) or Amp-L (LFP) Start would be an effective combo.

[GallenH]

Thanks for all of the info. But I still am curious as to whether the 136A alternator on the PW will effectively handle 200AH vs existing 100AH. Is there some way to calculate this?

[booster]

Originally Posted by GallenH

Thanks for all of the info. But I still am curious as to whether the 136A alternator on the PW will effectively handle 200AH vs existing 100AH. Is there some way to calculate this?

Wet cells or AGM? Do you run the frig on DC, if you have DC option on propane frig, while driving. Drive at night much? Dash air used while driving a on high fan?


136 amps will charge them, but the big question is how much the batteries will accept, assuming you have the wiring that will handle it, and how much power the van itself is using while driving. Most stock alternators don't like to go over about 50% of rated or they get too hot and get shorter life, so you would looking at having 60-70 amps continuous available but more in short time periods of maybe 15 minutes.



My guess is the van will maybe 25-50 depending on what is running an using power so not a lot left for the batteries to get sometimes.



With an alternator that size, I would definitely limit current to coach with one of the methods mentioned by others. Somewhere in the 40 amp range would probably be appropriate for a limit. That would charge wet cells at a higher than recommended rate on 200ah batteries and right on for AGMs. The wiring from the engine to the coach batteries may not be big enough to handle more than the 40 amps anyway.



The thing to remember is that batteries don't limit the charging until it is way, way, to high for them to be getting. They will overheat and get shortened life if given too much current for too long. That is why limiting is a very good idea.

[GeorgeRa]

Originally Posted by markopolo

Both devices are interesting. The current limiting of the Magnum ME-SBC seems to be PCB or FET temperature driven causing either a full interrupt or a reduced duty cycle. I'm not 100% certain of that though but that's all I could gather from the manual. No boost/buck so it's dependent on the capability of a separate charging device if one wants to meet specific charging criteria.
...................

This from my manual. If battery demand exceeds 30A it takes long time to pass 25A without interruption. I would prefer to if ME-SBC dial down above 25A to without interruption.

Originally Posted by GallenH

Thanks for all of the info. But I still am curious as to whether the 136A alternator on the PW will effectively handle 200AH vs existing 100AH. Is there some way to calculate this?

If you connect engine and house batteries with smart B>B charger you can set it up for any charge profile and maximum current.

If you add B>B charger capable to take power from 2 DC sources such as solar panels and alternator you will charge your batteries with correct profile from either alternator or solar panels.

Check your future batteries charging specs, then based on previous comments see if an existing alternator will suffice.

[RT-NY]

Is damaging the alternator really a significant concern when adding additional house batteries. From what I have seen a lot people routinely add a second 100AH AGM battery to the older Dodge Roadtreks, which, to the best of my knowledge do not have any kind of charger between the alternator and the battery. There is an isolator under the hood, but does that limit the current? Is there a danger of damaging the alternator in a case like this?

[booster]

Originally Posted by RT-NY

Is damaging the alternator really a significant concern when adding additional house batteries. From what I have seen a lot people routinely add a second 100AH AGM battery to the older Dodge Roadtreks, which, to the best of my knowledge do not have any kind of charger between the alternator and the battery. There is an isolator under the hood, but does that limit the current? Is there a danger of damaging the alternator in a case like this?

It can be an issue, especially on older vehicles with rebuilt alternators of unknown size and qaulity in them. What normally would happen if someone just slaps in an extra 100ah of battery on an old class b is that they also probably still have a diode isolator so lose .7v of charging voltage to it. They also probably have small wiring to van and lose some more voltage at higher charge rates. All of a sudden the 14.4v you see at the alternator are somewhere near float voltage at the batteries and they will charge, but very slowly, and the wiring may overheat in the process. There may also be 30, 40, 50, or 80 amp circuit breakers in the charging line that will keep cycling on and off. Roadtrek had issues, unacknowledged, when they took their systems off isolators and went to separators and also went to AGM batteries. We hear of lots of mystery clicking (of the breakers) and then after a period of wear abuse, no charging. Yep, people get by with it, but their batteries suffer from bad charging and they risk overheated wire hazards sometimes.



It is often said that they call them charging "systems" for a reason. They need to be a matched system to work properly. That includes the right charge voltage at the batteries, safe wire sizes, and appropriate charge profiles and current limiting if needed. All the above are contingent on the alternator also having the capacity to give the right amount of power without overheating.

[Jbell]

I have a 2001 Roadtrek. I have replaced my house batteries with 2 battle born 100 amp lithium batteries. I have not made any other changes to the alternator charging system. I have traveled approximately 10,000 miles with this system and have had very good results. As noted in a previous post I did replace one 50 amp circuit breaker ( a weak link) but, it's
cheap and easy to replace. I also boondock exclusively so I am never on shore power charging.

[Goldspace]

Originally Posted by booster

It can be an issue, especially on older vehicles with rebuilt alternators of unknown size and qaulity in them. What normally would happen if someone just slaps in an extra 100ah of battery on an old class b is that they also probably still have a diode isolator so lose .7v of charging voltage to it. They also probably have small wiring to van and lose some more voltage at higher charge rates. All of a sudden the 14.4v you see at the alternator are somewhere near float voltage at the batteries and they will charge, but very slowly, and the wiring may overheat in the process. There may also be 30, 40, 50, or 80 amp circuit breakers in the charging line that will keep cycling on and off. Roadtrek had issues, unacknowledged, when they took their systems off isolators and went to separators and also went to AGM batteries. We hear of lots of mystery clicking (of the breakers) and then after a period of wear abuse, no charging. Yep, people get by with it, but their batteries suffer from bad charging and they risk overheated wire hazards sometimes.



It is often said that they call them charging "systems" for a reason. They need to be a matched system to work properly. That includes the right charge voltage at the batteries, safe wire sizes, and appropriate charge profiles and current limiting if needed. All the above are contingent on the alternator also having the capacity to give the right amount of power without overheating.

I have a 2001 RT Popular on a Dodge chassis with two 75AH AGMs (Interstate DCM0075). The vehicle has the 136A alternator.

I agree with Booster that unregulated voltage directed to house batteries by the isolator on older Roadtreks can cook your batteries. That's happened to me.

I installed a Victron 30A DC-DC smart charger, and a Victron BMV-712 smart monitor. I removed the isolator but retained the factory 30A circuit breaker.

If my house batteries are depleted beyond 30% of capacity, the Charger bulk charges for only a short time at 30A then settles to lower amperage before enabling absorption charge at about 14.8V and 20A. I've programmed manufacturer specified Absorption and Float voltages into the charger.

This combination has worked extremely well for me, and I believe that it would be adaptable to higher capacity lead acid batteries as well.

[RT-NY]

Originally Posted by Jbell

I did replace one 50 amp circuit breaker ( a weak link) but, it's
cheap and easy to replace.

Did the circuit breaker burn out from being tripped too often because your batteries were drawing too much current?

[Jbell]

That is the only one I have ever replaced and that was about 5000 miles ago, so it doesn't seem to happen very often.

[nicaland]

Yes it will, or it has without issue for me. I have the same alternator and 210ah wet cells. I typically am using my inverter running the fridge and various battery chargers as well.