Battery Isolator 24v - 12v

Branderson · January 03, 2019, 04:20:05 PM

Hi gang,

I have two 12v starting batteries that are completely separate of my house batts. My 24v alternator charges these start batts but the problem is it cannot tell when both are fully charged and my 2nd batt will not get fully charged. I keep a battery charger on that 2nd batt so when I plug into shore power, I get it charged up. When I'm driving my chair, lights, and mirrors will pull from that 2nd batt and I've noticed that when I plug into shore, that is half strength after a full day of driving.

I'm told what I need is a battery isolator that will go from 24 - 12 volts but it seems that it's hard to find that on the net. All I see are 12v isolators. Does anyone know of an isolator that would fix this?

richard5933 · January 03, 2019, 04:27:52 PM

You need one of these:

http://www.vanner.com/battery-equalizers/

Just an example of some possibilities - you'll have to size according to your needs. There are other companies that make battery equalizers out there, but these are commonly used in buses. These allow you to evenly pull your 12v loads from the 24v battery bank without having one battery do all the work for that.

The way it sounds like you're doing this, it's going to be very difficult to not either have one battery always undercharged or one battery boiled over.

Oonrahnjay · January 03, 2019, 04:36:43 PM

Brad - I think your problem is that you're drawing 12V from one battery but your charging system is supplying 24V to the entire pair of batteries. All your 12V load is going on one battery.
Is this what you're thinking about? I think it's the solution for what you're trying to do.

http://www.vanner.com/battery-equalizers/

And yeah, what Richard said!

Geoff · January 03, 2019, 04:44:40 PM

What Richard says makes sense, but are your house batteries set up for 12v? If so, you need to move the 12v chassis lead to the house batteries and have a 12v alternator as well as your 24v alternator running off the engine. That is what I did, and a whole lot of other people.

Branderson · January 03, 2019, 05:00:10 PM

Thanks guys. Im gonna look into the equalizers. Im not looking to change my house battery set up.

richard5933 · January 03, 2019, 05:14:58 PM

IF you have a 12v house battery bank, another way to go is to use one of these:

https://www.sterling-power-usa.com/SterlingPower24volt-to-12volt-dc-to-dc-batterytobatterycharger.aspx

This allows your 12v house battery bank to charge from your 24v bus system whenever the bus engine is running. Totally eliminate any 12v loads coming from your 24v battery bank, and keeps things totally separate.

We've been running this for quite some time. Great success so far - charges the house batteries at up to 70 amps while on the road, no drain from the 24v system while parked. Bus alternator only charges the bus batteries - the Sterling battery-to-battery handles the house batteries. Really simply to change to this system and shouldn't require any actual changes to your house system.

Someone else on BCM recently installed one of these and posted a thread about it.

Oonrahnjay · January 03, 2019, 05:29:56 PM

Quote from: richard5933 on January 03, 2019, 05:14:58 PMIF you have a 12v house battery bank, another way to go is to use one of these:

https://www.sterling-power-usa.com/SterlingPower24volt-to-12volt-dc-to-dc-batterytobatterycharger.aspx ...

Thanks, Richard. That looks good. I'm going to have a look at that.

gumpy · January 03, 2019, 06:26:01 PM

Sounds like someone rewired your headlights to 12v and they are drawing directly from the battery bank. Change that back to 12v bulbs running in series on the 24v batteries (see MC9 schematic or the MCI service bulletin for converting the MC8 lights) and add an equalizer as indicated above. Your chair and mirrors won't pull any significant load.

buswarrior · January 04, 2019, 03:47:47 AM

As noted, a battery equalizer is needed.

However, it sounds like the damage may be done.

Both batteries can be damaged, one from under charging, the other by overcharging.

Get the equalizer, then put both batteries thru a charge and test program separately, to confirm or deny that they have been murdered.

Happy coaching!
Buswarrior

Branderson · January 04, 2019, 07:17:56 AM

Shouldn't be any damage at least to getting overcharged. I have a battery charger that charges it up once I plug into shore. It's hard for me to explain fully b/c I'm really relaying what is happening.

The alternator thinks the batteries are charged up b/c it reads only one of them are full so typically that second battery is not recharged by the time the first one is.

That is why I was thinking I need an isolator so the alternator can read both batteries but it sounds like an equalizer might be the fix.

I can get at least 6 or 7 starts before I'm really concerned about plugging in and making sure that 2nd battery is charged back up. However, I recently went on a trip from Alabama to Texas and realized that driving it that long drains that second battery b/c of my lights, dash, mirrors and magnetic TOAD lights. So I wanted to see if there is an easy way to fix this that doesn't cost a ton of money and changing the entire electrical set up.

richard5933 · January 04, 2019, 10:56:27 AM

If you are drawing chassis loads (lights, mirrors, toad, etc.) from the 24v battery bank while driving, then you absolutely need to have an equalizer.

Not an isolator - an isolator is designed to allow charging of a house battery bank from a chassis alternator in a way which prevents the house system from inadvertently running down the chassis batteries.

The equalizer is designed to allow you to safely draw 12v from a 24v battery bank, doing it evenly from both batteries. Sounds like the way you've got your 12v circuit tapped into the 24v battery bank it's only drawing from one battery. Also sounds like your chassis alternator is getting its voltage reading from the other battery.

Get a Vanner equalizer, install it according to the directions, and you should be good to go. You'll arrive at your destination with both of your batteries charged and ready to restart the coach.

Oonrahnjay · January 04, 2019, 12:03:53 PM

Quote from: richard5933 on January 04, 2019, 10:56:27 AMIf you are drawing chassis loads (lights, mirrors, toad, etc.) from the 24v battery bank while driving, then you absolutely need to have an equalizer. ....

Yep, And the alternator *will* sense from a pair of batteries set up for 24V (series). If one is "drawn low" by 12V being pulled from it, the alternator will over-charge the other battery. The three biggest killers of batteries are overcharging them, discharging them too deeply, and not bringing a discharged battery up to full charge before you begin discharging it again.

Geoff · January 04, 2019, 12:24:17 PM

A Vanner Equalizer is not a cheap solution, nor is the 24 to 12v reducer Gizmo. Most people just add a 12v alternator on the engine to the 12v house batteries for chassis 12v loads.

The last MC 8 I worked on had a defective Auto Zone lifetime automotive one wire Delco alternator on it, 12v and 60-90 amps to run the lights and charge the house batteries. Auto Zone gave me a free replacement. Even so, the alternator only cost $60.

richard5933 · January 04, 2019, 02:12:05 PM

Quote from: Geoff on January 04, 2019, 12:24:17 PM
A Vanner Equalizer is not a cheap solution, nor is the 24 to 12v reducer Gizmo. Most people just add a 12v alternator on the engine to the 12v house batteries for chassis 12v loads.

The last MC 8 I worked on had a defective Auto Zone lifetime automotive one wire Delco alternator on it, 12v and 60-90 amps to run the lights and charge the house batteries. Auto Zone gave me a free replacement. Even so, the alternator only cost $60.

Depending on how easy it is to install the alternator on the engine, this might be an alternative. Having a free pulley (or one that can be piggybacked) and a way to easily fabricate a mounting bracket would make the alternator doable. Of course, then he'd have to re-route the feed to the chassis 12v circuits to the house system - not difficult but extra steps above installing a Vanner.

I remember seeing Vanner equalizers for sale from time to time on all the three bus conversion sites, so perhaps a good used one is available. There are also some used ones on eBay, but you'd have to buy from someone trustworthy.

buswarrior · January 04, 2019, 05:37:21 PM

Quote from: Branderson on January 04, 2019, 07:17:56 AM
Shouldn't be any damage at least to getting overcharged. I have a battery charger that charges it up once I plug into shore. It's hard for me to explain fully b/c I'm really relaying what is happening.

The alternator thinks the batteries are charged up b/c it reads only one of them are full so typically that second battery is not recharged by the time the first one is.

Not how it works.

The voltage regulator is signalling the alternator make the 27 odd volts of charging power for your pair of batteries, hooked up in series, 24 volt system, it isn't "reading" an individual battery.

There is little to no power being taken off the first battery, but there is power being taken out of the second battery... that power not being system voltage, but half of it, the load is imbalanced. The charging system is continuing to make power, it is intended to charge 24 volts worth of battery. The first battery is being pounded with power it does not need, the second battery is receiving too little power to keep up with the loads on it, as you have discovered, and you have tried to cope with by charging it on arrival via shore power.

This is not sustainable. The second battery typically gets identified as failing first, due to the obvious low voltage, but the first battery has also been harmed by overcharging, and over time, has lost capacity too.

Lots of busnuts, lots of in-service coaches, have been there and done that, when trying to get 12 volts out of a 24 volt system.

You have to choose a strategy to correct this, or be prepared to purchase batteries more often than necessary.

What is the voltage of your house system?

Add up the total cost of each solution, a used equalizer quickly becomes a cheap and speedy solution.

A 12 volt alternator addition needs fabrication and a cable run forward. A house bank connection requires a house charging source while underway...

An equalizer goes into the battery compartment, 3 cables get attached and it's done.

Battery equalizers are plentiful in the bus junkyards, any transit bus with air conditioning built in the last 3 decades came equipped with one or a pair, depending on what they wanted to order, or what got built.

Buying one online, you get to pay someone for having retrieved it for you.

happy coaching!
buswarrior