run inverter off alternator?

[john61ct-SKO]

MC-614 is the good one, most adjustable.

Also check out Wakespeed WS500/APS AP500

Large-frame ~200A best for cool running if you can fit it, best to actually pull much lower than max rated for longevity, Leece Neville designed for firetrucks/ambulances is ideal.

 

[Native-SKO]

We used a 350A PennTex Industries, Inc. quad mount for our second (house) alternator.

 

[Doktari]

thanks for the ideas/explanation everyone.

i have an onan qd5500 which is not mounted yet, and this will run the a/c units while camping and if needed while driving.

I was just trying to find a way to (if this makes sense) utilize the excess power off the alternator while behind the wheel, my thinking being 'ive got it so i might as well use it'.

is this faulty thinking?

It’s not faulty thinking but I’m learning it’s not simple to alter the alternator charging system. For example; my alternator is very near the exhaust manifold and can overheat. Putting more load on the alternator can make it even hotter. I’m thinking of installing a cooling fan and ventilating the alternator with cool air from outside the engine compartment.
Also the stock ground cable from the engine to chassis and battery cable from the alternator may not be suitable for charging a big house battery.
Then there’s the diodes inside the alternator as part of the internal rectifier. These are what get hot electrically. If you have it rebuilt consider having high amp diodes installed. Ideally this is where a temperature sensor would be placed. If a potentiometer is installed to adjust the output then temperature can be controlled somewhat. Sitting in traffic idling is a good time to turn down the output because cooling air flow is low. And/Or turn off loads when hot conditions exist. There’s a lot of variables. There’s expensive external regulators with temperature sensors that reduce output automatically.

 

[john61ct-SKO]

And the diodes often get relocated off the alternator body to help with overall cooling.

Mark Grasser is a good vendor

 

[Native-SKO]

And the diodes often get relocated off the alternator body to help with overall cooling.

Mark Grasser is a good vendor

The PennTex alternator I installed in our bus has an external regulator which is mounted inside the cab. It has a decent heat sink to help dissipate heat and keep the diodes cool.

 

[matthews2001]

stupid question maybe, but...

Isn't the electrical load of a diesel bus running in daytime(no lights on) actually pretty low? I mean, charging the starter battery, a radio, a computer for the engine. Where else is electrical energy required?

I am thinking of a dc to dc charger for my 4 house batteries as I tried charging my house batteries while driving but never got a real good charge assuming because I had only 13.2-13.5 volts really (estimate).

 

[Doktari]

The blower can use a bunch of watts. Around 240 watts or 20 amps on high is what I was told. Headlights maybe 120 watts or 10 amps. Then charging as well.
A DC-DC Charger is another load but it’s voltage sensitive. If it doesn’t turn on until the starting battery is mostly charged then the loads might not overcurrent the alternator. If the battery to battery charger “sees” the voltage drop then it will shut off to let the voltage come back up.
Ive been looking at battery to battery chargers also. Which one are you getting? I’m leaning towards the Sterling Power 12-12/60 amp because it is programmable. But it costs more than the Renogy. What others are there?

 

[matthews2001]

Looking at the renogy 40 amp for $165 (amazon).

Not sure about the more expensive sterling, nor the programing function need/value.

I do have a 120 vac smart charger when hooked to shore power but I boondock more then not. I was thinking of using that off my inverter when driving, but it is old and the dc to dc will be good backup.

 

[jordantallent]

House battery size

First, a bit of information about alternators:
Alternators vary their output current in an attempt at keeping a set output voltage. As the load changes or the engine speed changes, the alternator adjusts to try and maintain that output voltage. Alternators are rated at maximum output at a certain *alternator shaft* speed. At speeds less than the rated speed, the output current is less than the rated current. The "minimum" current output at the "minumum" alternator rotational speed varies from alternator to alternator. Some are designed to output a lot of current at low speeds (those are expensive and are usually associated with special tasks, like powering a fire engine equipment bay) but most have relatively low power output at slow alternator rotational speeds ... usually about half that of rated power.


The chassis designers select alternators that will provide enough current to maintain the chassis systems at idle and not much more. At higher than idle speeds, the excess current capacity is used to charge the batteries. Once the chassis power requirements are met and the batteries are charged, the alternator cuts back the current thus reducing the load on the alternator.



We have a second alternator which is connected to our house batteries. It is a 350A unit that puts out about 200A at engine idle. This is enough current to power our air conditioner through our inverter. When the air conditioner is running at maximum, it pulls about 120A (DC 12V nominal) through the inverter. So as long as the engine is running, the alternator produces enough power to run the air conditioner.


Our house batteries and chassis batteries are isolated from one another, with a battery isolation relay between them so that I can connect them together if needed. Most of the time, they are run independent with the chassis alternator taking care of the chassis systems, and the house alternator taking care of the house systems. I designed the systems this way so that the house systems would not put additional loads on the chassis systems and vice versa.


Bear this in mind when extending the loads and functions of your chassis systems.

What size battery bank did you have to go with for the house batteries? That's the part I'm having a hard time getting a clear answer for. I only want to use the alternator and house batteries while driving. Not while engine off.

 

[Albatross]

What size battery bank did you have to go with for the house batteries? That's the part I'm having a hard time getting a clear answer for. I only want to use the alternator and house batteries while driving. Not while engine off.

There isn't a clear answer to that question other than "MORE".

The basic size of a battery or bank can be measured in Amp-Hours (Ah); this is a number that should be on the label of basically all batteries these days. Essentially, it tells you how much juice (in amps) a battery should be able to provide for 1 hour (under ideal conditions) before becoming discharged (dead). Old batteries will probably have less, and realistically you're never going to be perfectly charged up to 100%. Here's something from l'internatz that tells you more, better than I can:

https://battlebornbatteries.com/what-are-amps/ .

br> Essentially, when everything is off, all of your power is going to come from the house batteries; unless you've got a more complicated electrical system that automatically shuts-off the batteries whenever you're connected to shore power. Even so, without regular discharge cycles, you're likely to wind up with some "plating" in your batteries (depending on their chemistry) that will reduce their charge/max capacity. It's actually healthy for (most of) your batteries to let them actually do some work and power something and drain down halfway regularly. Even the superior Li-Ion chemistries like LiFePO4 benefit from a bit of a regular stretch.

Your alternator is attached to the engine to take (spinny) power from it and to push electricity into your "truck" batteries. There shouldn't be a cross-connection from your truck batteries to your house batteries without some kind of isolation circuit, such as a smart-isolator or some kind of DC-DC charger; particularly if you're using different battery chemistries, different battery sizes/form-factors, or you have alternate power sources such as solar. Without some method of charging your house batteries, they're just a big, heavy, expensive brick(s).

How big your house battery bank needs to be depends on what you want to use it for, and how long you'll need to use it before you can charge it up again. If your usage is something like a simple 12V fan and a light or two like in a Mack truck or something, you should be easily able to get by with just about any-old automotive-sized RV/marine battery. If you're looking to power an 800-Watt window A/C unit, a hot plate, all of your internal lights, and some other fancy doodads, then you'll need a lot more than any single battery can provide. Probably something like four 8D-sized batteries at a minimum. If you need all that to be powered overnight before the solar kicks on again in the morning, then I'd seriously consider eight.

If you have the chance of being caught in a week-long rainstorm, then I would seriously consider figuring out some way to charge them up, because that's too much battery to reasonably fit someplace without giving up something like water tank space and weight.

 

[Native-SKO]

What size battery bank did you have to go with for the house batteries? That's the part I'm having a hard time getting a clear answer for. I only want to use the alternator and house batteries while driving. Not while engine off.

To add to what Albatross wrote ....


The battery acts as a buffer in the electrical system. If you are going to ONLY run your electrical devices while the engine is running, then even a single house battery would work fine. In our rig, the chassis bank has two lead acid batteries. The house bank also has two lead acid batteries with an isolation relay (switched) between the house bank and the chassis bank.

 

[cadillackid]

I have 4 100 AH batteries in my house bank and 2 in my starting bank.. with an isolator.. I do shore charging whewn parked at home base just to make sure the batteries stay maintained..



I do sometimes use the batteries while parked engine off when i want to run heat and use my onboard network systems.. but otherwise im running..


my alternator needs the engine to be at 800-900 RPM to really start giving me good output.. so when im idling with all 3 A/C systems running my voltage drops back to 12.1 or 12.2 on the dash... some of that is pull-down by the high amperage of the system pull esp at night with the lights on.. thats pulling on my starter batteries unless I engage the isolator to connect all 6 together..



I havent found a time yet erven being stuck in heavy traffic for along time where the 2 starter batteries couldnt run all the systems.. but I will say that idling most alternators will stress unless they are designed for super high output at low RPM.. my Bosch SB200 does a decent job, however on a DTA360 the pulley is pretty large compared to other engines to get better belt pull.. its an older bus so it has V-belts which are notorious on small pulleys for slipping so IH runs a bit larger pulley..



there are Monster alternators sold (with monster prices) designed for high amp pull at lower RPMs.. typically fitted to Emergency vehicles.. a lot of how much battery you need to ballast out depends on how much you plan to idle and what your loads are.. and what tpye of batteries you plan to put in your bank..


Lead acid and AGM batteries wont recharge super fast.. so if I run my batteries down and then take off driving.. they back off on the number of amps they will take pretty quickly,, lithium batteries will take high amp charging for further up into their state of charge so you can replenish Amp hours quicker.. assuming your alternator is again designed for max output continuus duty.. I look at my battery banks backing off on amps it takes as a safety net to not pull too hard continuously on my alternator..