SmartGauge limitations in use

As in most electronic equipment, there are limits as to what SmartGauge can and cannot do. We prefer to warn customers about the limitations before they spend money, not afterwards.

Under normal deep cycle battery useage SmartGauge will accurately track the state of charge of the batteries. However it will not operate reliably under the following conditions.

SmartGauge will not work correctly where.........

1. The batteries have deteriorated to below 50% of their original capacity. Batteries above this level can be treated as a battery of a smaller capacity. Once the available capacity falls below 50% of it's original the battery is effectively broken (see SmartGauge FAQs). SmartGauge will not accurately track the state of charge of broken batteries. Manufacturers and professional users recommend 80% as being the limit below which batteries should be replaced. This is ok for engine start batteries where the ability to produce enormous currents is required but we consider it too high for deep cycle batteries and many people get useful life out of the batteries well below this level. Remember, SmartGauge is a battery state of charge meter. It is not a battery tester.
SmartGauge will not work correctly where.....

2. The discharge current is greatly in excess of normal discharge currents for deep cycle batteries and the discharge is continued for long periods of time.

Rather than try to explain this in words there is a graph here

An explanation by way of example is in order:-

Imagine you have a 400 amp hour battery bank. Discharging this battery bank at 400 amps would represent a discharge current of 100% on the graph. So look along the bottom to find 100%. Now follow the 100% line up until it intersects the blue graph line. Follow this across to the left axis and you will see that the maximum permissible discharge time at this discharge rate is just about 15 minutes. But remember that, as a result of Peukert's effect, the batteries would have been discharged to 50% state of charge after 14 minutes anyway.

Discharging at 160 amps would represent a 40% discharge rate. Follow this line up to the blue graph line, then across to the left axis and you will see that the maximum permissible time at this discharge rate is 45 minutes. After 44 minutes the batteries would be discharged to 50% at this discharge rate with a typical Peukert's exponent of 1.3

Discharging this same battery bank at 800 amps would reach the acceptable time limit at around 7 minutes. But you only have 6 minutes run time available anyway at this discharge rate (see the Peukert Calculator)

Staying within these limits is staying within normal useage for deep cycle batteries.

So what are the effects of going outside these limits?

Going outside the limits may cause SmartGauge to not accurately track the state of charge during the discharge and immediately following the use of the heavy draw equipment.

If this is the type of use your batteries are getting, then the battery bank simply isn't big enough. Your battery bank needs to be increased in size by about 400%

This is not a limitation of SmartGauge. It is a limitation of deep cycle batteries. They are not designed to provide such enormous discharge currents and the available capacity from them can vary by up to 200% between two identical batteries of the same age. That is what engine start batteries are designed for.

If these limits are not adhered to then the battery state of charge as indicated by SmartGauge may not always be accurate immediately following use of the equipment. It will however "catch up" over a short period of time following use of the equipment.

SmartGauge is designed to monitor battery state of charge on deep cycle battery banks that are being used as deep cycle battery banks. Not as engine start batteries.

To put this in persepctive. A typical battery bank is around 400 amp hours. Running a heavy duty full size vacuum cleaner (via an inverter) from this bank will draw around 140 amps. This represents a 35% discharge rate. So using the graph you can see that this discharge current could be sustained for around an hour before it started to cause problems with the state of charge calculations. However you only have 52 minutes run time from fully charged to 50% anyway at this discharge rate.

It is something that will not affect 99% of users. But if you are abusing your batteries with extremely high discharge currents for long periods of time it is something you should be aware of.

In general, and for those who can't be bothered understanding the above, SmartGauge will operate reliably if the total discharge time is more than about 3 hours. If you are discharging your batteries in a time period much shorter than this then not only are you destroying your batteries extremely quickly (they will probably last a few months at the most) but also SmartGauge may not always accurately track the state of charge.

Another way to phrase it is this. If you are abusing your batteries then SmartGauge may not track the state of charge accurately during, and immediately following, the abuse. There is no way to calculate the effect of battery abuse on the state of charge.


Web site and all contents Copyright SmartGauge Electronics 2005, 2006, 2007, 2008. All rights reserved.
Page last updated 02/04/2008.
Website best viewed on a computer of some sort.