Alternator charging

[XERTYX]

Ok so not to overpost but I didn't want to get off topic on the other thread as that one was addressing whether or not to turn off solar charging while alternator charging. I think that was addressed to my satisfaction at least. So I pose another question. 

1: What number of amps could I expect to get from a typical medium duty alternator? I know alternators arent all created equally nor or engines also there are variables AC/heater usage, radio usage, etc etc.

2: What value inline fuse/ DC circuit breaker should I use?

3: If I happened to have a beefy alternator what is the best method of limiting current to prevent too rapid of a charge to the house battery?

I intend to buy either a Dodge Caravan or Chrysler Town and Country due to the stow and go seats which I'd remove for more storage. The build would include a redarc dual sensing battery Isolator mentioned in the other post. 2 100 watt monocrystalline panels with tilt capability and an MPPT charge controller. 2 12V marine deep cycle batteries (I believe the ones I researched were 120AH) 

Originally I had planned to use 4 100 watt panels and 4 12V marine deep cycle batteries. Due to budget I think i could make do with the smaller setup and add a camper trailer later and expand from there.

The only appliance that would be full time used would be an alpicool c20 which would be no problem on 200W. I'd charge my phone and small tablet every day. And that's the bulk of the appliances I'd use. Occasionally a 700W microwave. And semi occasionally a 900W coffee pot but only to brew and then switched off and the liquid put in a thermos. I dont think that's too ambitious a goal. Most cooking would be on propane. Heating also propane. Eventually I might add a fantastic fan but hopefully I'd have the travel trailer before that point.

So, advice?

 

[frater secessus]

Caution:  I may be drunk or stupid, you have no way of knowing at this point.  

1.  I don't know but it wil be in the vehicle specs

2.  fusing is typically 1.5x the normal current.   See #3 below.  Wiser folk please correct me if I am off base.

3.  the battery is likely the bottleneck for current.  Flooded batteries will likely accept something like C/5 maximum (20A per 100Ah of rated Capacity).  AGM will probably be around C/3 (33A per 100Ah of capacity).  On the other hand lithium can slurp power greedily around 1C (100A per 100Ah of capacity)!  

Practical example for #3.  I have 220Ah bank made of golf cart batteries.  I use a 75A-rated Battery Doctor voltage sensing relay for alternator charging.   When deeply cycled they pull a little over 40A from the alternator, which is right around the expected C/5 value (220/5 = 44).   They make that relay in higher amp (and more $$$) models but my batteries will never pull even the 75A duty rating.

Sidenote:  alternators are cooled by airflow when driving.  Idling the vehicle to charge the house batteries is unlikely to make the alternator happy to see you; it may make the NAPA parts guy happy to see you.  Newer/smarter alternators monitor their own temps and limit current to protect themselves, but I don't know the details of that implementation or which vehicles do that.  I seem to remember Tx2Sturgis being intimately acquainted with alternator internals and electronics;  maybe he will stop in and get us on the right path.

 

[Weight]

Your vehicle alternator will never over charge a house battery bank. You should be worrying about how to complete the charging before you need the bank. If you install some non-oem alternator, the answer is; the regulator for the alternator does that job.

 

[frater secessus]

An alternator could overcharge a lithium bank.

 

[B and C]

A lithium bank should have some sort of battery monitoring system (BMS). The BMS should keep the battery from over charging/discharging.

 

[Weight]

A oem alternator will not over charge any battery unless something is wrong with the vehicle.

 

[VanTalk00]

[quote pid='431456' dateline='1546664345']
So, advice?
[/quote]

I just bought a Battle Born package and included is a Battery Isolation Manager.  I got the attached pdf as further documentation of just what it does.  I know there are other solutions, but this works well with the rest of the Victron equipment.  

I believe the intent is to avoid overtaxing the alternator or over charging the batteries.

Jim

 

[makenmend]

'' Originally I had planned to use 4 100 watt panels and 4 12V marine deep cycle batteries. Due to budget I think i could make do with the smaller setup and add a camper trailer later and expand from there ''

ZERTYX, try and define what your requirements will be, then can plan on your battery/solar sizing. As you say you can up grade as and when funds/resources allow. 200 Watt and 200AH should be a very good starting point.

MM

 

[Doubleone]

1: Max amperage is built into the alternator design.  Look at a replacement parts catalog, alternator identification chart, and sometimes stamped on the alternator.  Newer cars are around 80 amps, classic cars 50-60 amps, gasoline trucks are 90-120-ish.   Max amps is just that, peak possible output in amps.  There is a strict relationship between volts and amps, and alternator output varies depending on how discharged your battery is... the more discharged your battery the more amps from the alternator.  If voltage in the battery is near full the alternator doesn't really do much, if the battery is really low the alternator provides a high amperage.  As battery volts start coming back toward full charge the amperage tapers off lower and lower.  Don't think of amperage as pushing electricity, its more like the battery pulls the amperage depending on how low the charge is.  It's like water flowing through a dam, if water is at the same level on both sides of the dam, nothing flows.  You will rarely see peak amperage from an alternator unless the battery is really dead.  In a battery used for starting you might see a peak at half amperage capacity for a couple minutes and amperage quickly tapering off.  A start battery is a single battery that stays almost fully charged all the time, so it only needs a quick low amperage recharge.  On the other hand, severely discharged house batteries could pull very high amps for a very long time, causing a lot of heat in the alternator.  Using an alternator to charge house batteries can be done, but as many will point out, this is not ideal for the alternator.  

2: 150 amp mega fuse on each individual house battery.

3: Beefy-ness is vague and subjective.  You're likely thinking higher rated amp output is more beefy, I'm thinking longer rated duty cycle is more beefy.  Duty cycle is the amount of on-time at maximum amp rate.  For example, a 100 amp car alternator I'd guess is about a 20% duty cycle (20% on time and 80% rest/cooling) but a 100 amp marine alternator may be 80-100% duty cycle (80% on, 20% rest).  Think of duty cycle as if two people were comparing how fast they can run.  They both might run at the same peak speed, but one is going to tire out sooner than the other... one is more 'beefy'.  

If given no other options (solar, generator, shore power) and you're absolutely dead set on using an alternator... the highest quality set up would be a marine alternator with charge controller but we're talking huge $$$$, and at that point you might as well go solar or buy a small generator and a smart power converter.  Next best alternator set-up would be to use a marine DC charge controller to limit amperage and reduce electrolyte boil off, in the range of $$$, but again other options exist at equivalent costs.  What you can get away for a short while... is a battery isolator ($$) and keep the house batteries as fully charged as possible at all times.  At the very least, use an automotive battery charger for the house and plug it in whenever you can.

Here's the conundrum... your choices are high output, cheap, and reliable... you can only have two...