Hello! Log in or Register   |  Help  |  Donate  |  Buy Shirts See all banner ads | Advertise on TheSamba.com  
TheSamba.com
 
how long to charge a battery
Forum Index -> Bay Window Bus Share: Facebook Twitter
Reply to topic
Print View
Quick sort: Show newest posts on top | Show oldest posts on top View previous topic :: View next topic  
Author Message
SGKent Premium Member
Samba Member


Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
SGKent is offline 

PostPosted: Fri Aug 12, 2016 7:37 pm    Post subject: how long to charge a battery Reply with quote

Besides the normal cautions when charging - no frozen batteries, water level correct, no smoking or sparks due to hydrogen, eye and skin protection from acid. here is a way to roughly calculate how long to charge a battery. You should know this because some chargers may say they are automatic but they aren't always as promised. Another way is to check the specific gravity if you have the bulb and access to the battery acid.

First you must know if your battery is AGM, maintenance free, or calcium based. If so you will use a different part of the chart. Second you must know the Reserve Capacity of your battery, which you can usually find online if you know the battery manufacture and model. In my case it is an Interstate Mega-Tron Plus 48 / h6, That is a calcium silver battery with AGM construction and is meant to be maintenance free although I do check water levels. This battery has a reserve capacity of 115.

Multiple the RC x .6. In my case that is 115 x .6 = 69
Measure the voltage with no load on it - called open cell voltage. Mine is 12.55 volts.
Check the battery temperature with a laser gun if you have it. It is 90 F here.
On the chart that shows the battery is appx 60% charged which sounds about right as it has been sitting awhile.
Multiple 40% needed to get to 100% (100% - 60% = 40%) X the total we got of (RC x .6) so 40% x 69 = 27.6. [remember the 69 came from 115 RC for my battery x .6)
Add 15% for battery internal resistance, This is a standard. 27.6 + 15% = 31.74.
Divide the number (in this case 31.74) by the amps you will be charging at per hour and that is how long to charge. I will charge at 10 amps so 31.74 / 10 = about 3 hours to get to a full charge. If I charged at 2 amps it would be about 15 - 16 hours.

I like to remove the battery once a year, check fluid level and charge it to 100% unless it has been driven often. Then I wipe the area around the battery with water and baking soda to neutralize any acid that is on the paint and metal. Don't get any in the battery or it will kill it. I then clean the terminals and put a little Vaseline on them before putting it the cables back on. If you have a label printer you can mark + and - on the side of the battery as on a bus it is hard to see that if the marks are on top.

Image may have been reduced in size. Click image to view fullscreen.

_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
SGKent Premium Member
Samba Member


Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
SGKent is offline 

PostPosted: Sat Dec 23, 2017 7:38 pm    Post subject: Re: how long to charge a battery Reply with quote

just had to charge the battery since it has been sitting awhile. Formula works like a champ. Be sure to measure before you start charging because the surface voltage will throw the resting open cell voltage off. Once can also measure the battery acid however that is harder in a VW bus because one has to pull the battery to be able to do that.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
SGKent Premium Member
Samba Member


Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
SGKent is offline 

PostPosted: Sun Jul 15, 2018 1:53 pm    Post subject: Re: how long to charge a battery Reply with quote

correction - 48 Mega-tron MTP 48/H6 is wet cell. Holding up well. I added a CTEK MXS 5.0 battery maintenance charger to it for when the bus sits too many weeks and the charge drains. CTEK makes the Porsche labeled maintenance chargers. It also has a step that can remove sulfates from the battery, extending its life. I chose this model based on reviews and an article where someone watched the charging pulses on an oscilloscope to determine which chargers were best designed for maintaining a vehicle battery.

Interstate MTP 48-H6 battery

Image may have been reduced in size. Click image to view fullscreen.


Part Number MTP-48/H6
Group Size H6
Cold Cranking Amps 730
Cranking Amps 910
Reserve Capacity (RC) @ 25 hr 115
Amp Hours (Ah) @ 20 Hr 70
Length 11
Width 6 15/16
Height 7 1/2
Weight 38.8
Termination Code Common Code A
Voltage 12

CTEK charger

Image may have been reduced in size. Click image to view fullscreen.


Porsche charger

Image may have been reduced in size. Click image to view fullscreen.

_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
telford dorr
Samba Member


Joined: March 11, 2009
Posts: 3547
Location: San Diego (Encinitas)
telford dorr is offline 

PostPosted: Sun Jul 15, 2018 5:46 pm    Post subject: Re: how long to charge a battery Reply with quote

Good stuff!

The most important point is that full charge specific gravity INCREASES with lower temperature. Not intuitive!

Not clear if the pulse charging commonly sold actually helps sulfate removal or not. I built a couple of experimental units and the best I can say is that it dosen't hurt. The most viable technique seems to charge the battery for a while, then discharge it a bit. This seems to even out the metalic lead deposit on the battery plates. The main drawback is it is slow (two forward, one back) and it wastes a bunch of energy, as you have to dump that discharge energy somewhere. Now maybe a dual battery charger setup where the discharge phase of one battery dumps its energy into the charge phase of a second battery, and vis versa. Don't know. Will take a bunch of parts and time to find out...(some day).
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)
Back to top
View user's profile Send private message Visit poster's website Gallery Classifieds Feedback
Display posts from previous:   
Reply to topic    Forum Index -> Bay Window Bus All times are Mountain Standard Time/Pacific Daylight Savings Time
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum

About | Help! | Advertise | Donate | Premium Membership | Privacy/Terms of Use | Contact Us | Site Map
Copyright © 1996-2023, Everett Barnes. All Rights Reserved.
Not affiliated with or sponsored by Volkswagen of America | Forum powered by phpBB
Links to eBay or other vendor sites may be affiliate links where the site receives compensation.